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Diffstat (limited to 'src/tail.c')
| -rw-r--r-- | src/tail.c | 2478 |
1 files changed, 2478 insertions, 0 deletions
diff --git a/src/tail.c b/src/tail.c new file mode 100644 index 0000000..f293551 --- /dev/null +++ b/src/tail.c @@ -0,0 +1,2478 @@ +/* tail -- output the last part of file(s) + Copyright (C) 1989-2023 Free Software Foundation, Inc. + + This program is free software: you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation, either version 3 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program. If not, see <https://www.gnu.org/licenses/>. */ + +/* Can display any amount of data, unlike the Unix version, which uses + a fixed size buffer and therefore can only deliver a limited number + of lines. + + Original version by Paul Rubin <phr@ocf.berkeley.edu>. + Extensions by David MacKenzie <djm@gnu.ai.mit.edu>. + tail -f for multiple files by Ian Lance Taylor <ian@airs.com>. + inotify back-end by Giuseppe Scrivano <gscrivano@gnu.org>. */ + +#include <config.h> + +#include <stdio.h> +#include <getopt.h> +#include <sys/types.h> +#include <signal.h> + +#include "system.h" +#include "argmatch.h" +#include "assure.h" +#include "cl-strtod.h" +#include "fcntl--.h" +#include "iopoll.h" +#include "isapipe.h" +#include "posixver.h" +#include "quote.h" +#include "safe-read.h" +#include "stat-size.h" +#include "stat-time.h" +#include "xbinary-io.h" +#include "xdectoint.h" +#include "xnanosleep.h" +#include "xstrtol.h" +#include "xstrtod.h" + +#if HAVE_INOTIFY +# include "hash.h" +# include <poll.h> +# include <sys/inotify.h> +#endif + +/* Linux can optimize the handling of local files. */ +#if defined __linux__ || defined __ANDROID__ +# include "fs.h" +# include "fs-is-local.h" +# if HAVE_SYS_STATFS_H +# include <sys/statfs.h> +# elif HAVE_SYS_VFS_H +# include <sys/vfs.h> +# endif +#endif + +/* The official name of this program (e.g., no 'g' prefix). */ +#define PROGRAM_NAME "tail" + +#define AUTHORS \ + proper_name ("Paul Rubin"), \ + proper_name ("David MacKenzie"), \ + proper_name ("Ian Lance Taylor"), \ + proper_name ("Jim Meyering") + +/* Number of items to tail. */ +#define DEFAULT_N_LINES 10 + +/* Special values for dump_remainder's N_BYTES parameter. */ +#define COPY_TO_EOF UINTMAX_MAX +#define COPY_A_BUFFER (UINTMAX_MAX - 1) + +/* FIXME: make Follow_name the default? */ +#define DEFAULT_FOLLOW_MODE Follow_descriptor + +enum Follow_mode +{ + /* Follow the name of each file: if the file is renamed, try to reopen + that name and track the end of the new file if/when it's recreated. + This is useful for tracking logs that are occasionally rotated. */ + Follow_name = 1, + + /* Follow each descriptor obtained upon opening a file. + That means we'll continue to follow the end of a file even after + it has been renamed or unlinked. */ + Follow_descriptor = 2 +}; + +/* The types of files for which tail works. */ +#define IS_TAILABLE_FILE_TYPE(Mode) \ + (S_ISREG (Mode) || S_ISFIFO (Mode) || S_ISSOCK (Mode) || S_ISCHR (Mode)) + +static char const *const follow_mode_string[] = +{ + "descriptor", "name", nullptr +}; + +static enum Follow_mode const follow_mode_map[] = +{ + Follow_descriptor, Follow_name, +}; + +struct File_spec +{ + /* The actual file name, or "-" for stdin. */ + char *name; + + /* Attributes of the file the last time we checked. */ + off_t size; + struct timespec mtime; + dev_t dev; + ino_t ino; + mode_t mode; + + /* The specified name initially referred to a directory or some other + type for which tail isn't meaningful. Unlike for a permission problem + (tailable, below) once this is set, the name is not checked ever again. */ + bool ignore; + + /* See the description of fremote. */ + bool remote; + + /* A file is tailable if it exists, is readable, and is of type + IS_TAILABLE_FILE_TYPE. */ + bool tailable; + + /* File descriptor on which the file is open; -1 if it's not open. */ + int fd; + + /* The value of errno seen last time we checked this file. */ + int errnum; + + /* 1 if O_NONBLOCK is clear, 0 if set, -1 if not known. */ + int blocking; + +#if HAVE_INOTIFY + /* The watch descriptor used by inotify. */ + int wd; + + /* The parent directory watch descriptor. It is used only + * when Follow_name is used. */ + int parent_wd; + + /* Offset in NAME of the basename part. */ + size_t basename_start; +#endif + + /* See description of DEFAULT_MAX_N_... below. */ + uintmax_t n_unchanged_stats; +}; + +/* Keep trying to open a file even if it is inaccessible when tail starts + or if it becomes inaccessible later -- useful only with -f. */ +static bool reopen_inaccessible_files; + +/* If true, interpret the numeric argument as the number of lines. + Otherwise, interpret it as the number of bytes. */ +static bool count_lines; + +/* Whether we follow the name of each file or the file descriptor + that is initially associated with each name. */ +static enum Follow_mode follow_mode = Follow_descriptor; + +/* If true, read from the ends of all specified files until killed. */ +static bool forever; + +/* If true, monitor output so we exit if pipe reader terminates. */ +static bool monitor_output; + +/* If true, count from start of file instead of end. */ +static bool from_start; + +/* If true, print filename headers. */ +static bool print_headers; + +/* Character to split lines by. */ +static char line_end; + +/* When to print the filename banners. */ +enum header_mode +{ + multiple_files, always, never +}; + +/* When tailing a file by name, if there have been this many consecutive + iterations for which the file has not changed, then open/fstat + the file to determine if that file name is still associated with the + same device/inode-number pair as before. This option is meaningful only + when following by name. --max-unchanged-stats=N */ +#define DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS 5 +static uintmax_t max_n_unchanged_stats_between_opens = + DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS; + +/* The process ID of the process (presumably on the current host) + that is writing to all followed files. */ +static pid_t pid; + +/* True if we have ever read standard input. */ +static bool have_read_stdin; + +/* If nonzero, skip the is-regular-file test used to determine whether + to use the lseek optimization. Instead, use the more general (and + more expensive) code unconditionally. Intended solely for testing. */ +static bool presume_input_pipe; + +/* If nonzero then don't use inotify even if available. */ +static bool disable_inotify; + +/* For long options that have no equivalent short option, use a + non-character as a pseudo short option, starting with CHAR_MAX + 1. */ +enum +{ + RETRY_OPTION = CHAR_MAX + 1, + MAX_UNCHANGED_STATS_OPTION, + PID_OPTION, + PRESUME_INPUT_PIPE_OPTION, + LONG_FOLLOW_OPTION, + DISABLE_INOTIFY_OPTION +}; + +static struct option const long_options[] = +{ + {"bytes", required_argument, nullptr, 'c'}, + {"follow", optional_argument, nullptr, LONG_FOLLOW_OPTION}, + {"lines", required_argument, nullptr, 'n'}, + {"max-unchanged-stats", required_argument, nullptr, + MAX_UNCHANGED_STATS_OPTION}, + {"-disable-inotify", no_argument, nullptr, + DISABLE_INOTIFY_OPTION}, /* do not document */ + {"pid", required_argument, nullptr, PID_OPTION}, + {"-presume-input-pipe", no_argument, nullptr, + PRESUME_INPUT_PIPE_OPTION}, /* do not document */ + {"quiet", no_argument, nullptr, 'q'}, + {"retry", no_argument, nullptr, RETRY_OPTION}, + {"silent", no_argument, nullptr, 'q'}, + {"sleep-interval", required_argument, nullptr, 's'}, + {"verbose", no_argument, nullptr, 'v'}, + {"zero-terminated", no_argument, nullptr, 'z'}, + {GETOPT_HELP_OPTION_DECL}, + {GETOPT_VERSION_OPTION_DECL}, + {nullptr, 0, nullptr, 0} +}; + +void +usage (int status) +{ + if (status != EXIT_SUCCESS) + emit_try_help (); + else + { + printf (_("\ +Usage: %s [OPTION]... [FILE]...\n\ +"), + program_name); + printf (_("\ +Print the last %d lines of each FILE to standard output.\n\ +With more than one FILE, precede each with a header giving the file name.\n\ +"), DEFAULT_N_LINES); + + emit_stdin_note (); + emit_mandatory_arg_note (); + + fputs (_("\ + -c, --bytes=[+]NUM output the last NUM bytes; or use -c +NUM to\n\ + output starting with byte NUM of each file\n\ +"), stdout); + fputs (_("\ + -f, --follow[={name|descriptor}]\n\ + output appended data as the file grows;\n\ + an absent option argument means 'descriptor'\n\ + -F same as --follow=name --retry\n\ +"), stdout); + printf (_("\ + -n, --lines=[+]NUM output the last NUM lines, instead of the last %d;\n\ + or use -n +NUM to skip NUM-1 lines at the start\n\ +"), + DEFAULT_N_LINES + ); + printf (_("\ + --max-unchanged-stats=N\n\ + with --follow=name, reopen a FILE which has not\n\ + changed size after N (default %d) iterations\n\ + to see if it has been unlinked or renamed\n\ + (this is the usual case of rotated log files);\n\ + with inotify, this option is rarely useful\n\ +"), + DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS + ); + fputs (_("\ + --pid=PID with -f, terminate after process ID, PID dies\n\ + -q, --quiet, --silent never output headers giving file names\n\ + --retry keep trying to open a file if it is inaccessible\n\ +"), stdout); + fputs (_("\ + -s, --sleep-interval=N with -f, sleep for approximately N seconds\n\ + (default 1.0) between iterations;\n\ + with inotify and --pid=P, check process P at\n\ + least once every N seconds\n\ + -v, --verbose always output headers giving file names\n\ +"), stdout); + fputs (_("\ + -z, --zero-terminated line delimiter is NUL, not newline\n\ +"), stdout); + fputs (HELP_OPTION_DESCRIPTION, stdout); + fputs (VERSION_OPTION_DESCRIPTION, stdout); + fputs (_("\ +\n\ +NUM may have a multiplier suffix:\n\ +b 512, kB 1000, K 1024, MB 1000*1000, M 1024*1024,\n\ +GB 1000*1000*1000, G 1024*1024*1024, and so on for T, P, E, Z, Y, R, Q.\n\ +Binary prefixes can be used, too: KiB=K, MiB=M, and so on.\n\ +\n\ +"), stdout); + fputs (_("\ +With --follow (-f), tail defaults to following the file descriptor, which\n\ +means that even if a tail'ed file is renamed, tail will continue to track\n\ +its end. This default behavior is not desirable when you really want to\n\ +track the actual name of the file, not the file descriptor (e.g., log\n\ +rotation). Use --follow=name in that case. That causes tail to track the\n\ +named file in a way that accommodates renaming, removal and creation.\n\ +"), stdout); + emit_ancillary_info (PROGRAM_NAME); + } + exit (status); +} + +/* Ensure exit, either with SIGPIPE or EXIT_FAILURE status. */ +static void +die_pipe (void) +{ + raise (SIGPIPE); + exit (EXIT_FAILURE); +} + +/* If the output has gone away, then terminate + as we would if we had written to this output. */ +static void +check_output_alive (void) +{ + if (! monitor_output) + return; + + if (iopoll (-1, STDOUT_FILENO, false) == IOPOLL_BROKEN_OUTPUT) + die_pipe (); +} + +MAYBE_UNUSED static bool +valid_file_spec (struct File_spec const *f) +{ + /* Exactly one of the following subexpressions must be true. */ + return ((f->fd == -1) ^ (f->errnum == 0)); +} + +static char const * +pretty_name (struct File_spec const *f) +{ + return (STREQ (f->name, "-") ? _("standard input") : f->name); +} + +/* Record a file F with descriptor FD, size SIZE, status ST, and + blocking status BLOCKING. */ + +static void +record_open_fd (struct File_spec *f, int fd, + off_t size, struct stat const *st, + int blocking) +{ + f->fd = fd; + f->size = size; + f->mtime = get_stat_mtime (st); + f->dev = st->st_dev; + f->ino = st->st_ino; + f->mode = st->st_mode; + f->blocking = blocking; + f->n_unchanged_stats = 0; + f->ignore = false; +} + +/* Close the file with descriptor FD and name FILENAME. */ + +static void +close_fd (int fd, char const *filename) +{ + if (fd != -1 && fd != STDIN_FILENO && close (fd)) + { + error (0, errno, _("closing %s (fd=%d)"), quoteaf (filename), fd); + } +} + +static void +write_header (char const *pretty_filename) +{ + static bool first_file = true; + + printf ("%s==> %s <==\n", (first_file ? "" : "\n"), pretty_filename); + first_file = false; +} + +/* Write N_BYTES from BUFFER to stdout. + Exit immediately on error with a single diagnostic. */ + +static void +xwrite_stdout (char const *buffer, size_t n_bytes) +{ + if (n_bytes > 0 && fwrite (buffer, 1, n_bytes, stdout) < n_bytes) + { + clearerr (stdout); /* To avoid redundant close_stdout diagnostic. */ + error (EXIT_FAILURE, errno, _("error writing %s"), + quoteaf ("standard output")); + } +} + +/* Read and output N_BYTES of file PRETTY_FILENAME starting at the current + position in FD. If N_BYTES is COPY_TO_EOF, then copy until end of file. + If N_BYTES is COPY_A_BUFFER, then copy at most one buffer's worth. + Return the number of bytes read from the file. */ + +static uintmax_t +dump_remainder (bool want_header, char const *pretty_filename, int fd, + uintmax_t n_bytes) +{ + uintmax_t n_written; + uintmax_t n_remaining = n_bytes; + + n_written = 0; + while (true) + { + char buffer[BUFSIZ]; + size_t n = MIN (n_remaining, BUFSIZ); + size_t bytes_read = safe_read (fd, buffer, n); + if (bytes_read == SAFE_READ_ERROR) + { + if (errno != EAGAIN) + error (EXIT_FAILURE, errno, _("error reading %s"), + quoteaf (pretty_filename)); + break; + } + if (bytes_read == 0) + break; + if (want_header) + { + write_header (pretty_filename); + want_header = false; + } + xwrite_stdout (buffer, bytes_read); + n_written += bytes_read; + if (n_bytes != COPY_TO_EOF) + { + n_remaining -= bytes_read; + if (n_remaining == 0 || n_bytes == COPY_A_BUFFER) + break; + } + } + + return n_written; +} + +/* Call lseek with the specified arguments, where file descriptor FD + corresponds to the file, FILENAME. + Give a diagnostic and exit nonzero if lseek fails. + Otherwise, return the resulting offset. */ + +static off_t +xlseek (int fd, off_t offset, int whence, char const *filename) +{ + off_t new_offset = lseek (fd, offset, whence); + char buf[INT_BUFSIZE_BOUND (offset)]; + char *s; + + if (0 <= new_offset) + return new_offset; + + s = offtostr (offset, buf); + switch (whence) + { + case SEEK_SET: + error (EXIT_FAILURE, errno, _("%s: cannot seek to offset %s"), + quotef (filename), s); + break; + case SEEK_CUR: + error (EXIT_FAILURE, errno, _("%s: cannot seek to relative offset %s"), + quotef (filename), s); + break; + case SEEK_END: + error (EXIT_FAILURE, errno, + _("%s: cannot seek to end-relative offset %s"), + quotef (filename), s); + break; + default: + unreachable (); + } +} + +/* Print the last N_LINES lines from the end of file FD. + Go backward through the file, reading 'BUFSIZ' bytes at a time (except + probably the first), until we hit the start of the file or have + read NUMBER newlines. + START_POS is the starting position of the read pointer for the file + associated with FD (may be nonzero). + END_POS is the file offset of EOF (one larger than offset of last byte). + Return true if successful. */ + +static bool +file_lines (char const *pretty_filename, int fd, uintmax_t n_lines, + off_t start_pos, off_t end_pos, uintmax_t *read_pos) +{ + char buffer[BUFSIZ]; + size_t bytes_read; + off_t pos = end_pos; + + if (n_lines == 0) + return true; + + /* Set 'bytes_read' to the size of the last, probably partial, buffer; + 0 < 'bytes_read' <= 'BUFSIZ'. */ + bytes_read = (pos - start_pos) % BUFSIZ; + if (bytes_read == 0) + bytes_read = BUFSIZ; + /* Make 'pos' a multiple of 'BUFSIZ' (0 if the file is short), so that all + reads will be on block boundaries, which might increase efficiency. */ + pos -= bytes_read; + xlseek (fd, pos, SEEK_SET, pretty_filename); + bytes_read = safe_read (fd, buffer, bytes_read); + if (bytes_read == SAFE_READ_ERROR) + { + error (0, errno, _("error reading %s"), quoteaf (pretty_filename)); + return false; + } + *read_pos = pos + bytes_read; + + /* Count the incomplete line on files that don't end with a newline. */ + if (bytes_read && buffer[bytes_read - 1] != line_end) + --n_lines; + + do + { + /* Scan backward, counting the newlines in this bufferfull. */ + + size_t n = bytes_read; + while (n) + { + char const *nl; + nl = memrchr (buffer, line_end, n); + if (nl == nullptr) + break; + n = nl - buffer; + if (n_lines-- == 0) + { + /* If this newline isn't the last character in the buffer, + output the part that is after it. */ + xwrite_stdout (nl + 1, bytes_read - (n + 1)); + *read_pos += dump_remainder (false, pretty_filename, fd, + end_pos - (pos + bytes_read)); + return true; + } + } + + /* Not enough newlines in that bufferfull. */ + if (pos == start_pos) + { + /* Not enough lines in the file; print everything from + start_pos to the end. */ + xlseek (fd, start_pos, SEEK_SET, pretty_filename); + *read_pos = start_pos + dump_remainder (false, pretty_filename, fd, + end_pos); + return true; + } + pos -= BUFSIZ; + xlseek (fd, pos, SEEK_SET, pretty_filename); + + bytes_read = safe_read (fd, buffer, BUFSIZ); + if (bytes_read == SAFE_READ_ERROR) + { + error (0, errno, _("error reading %s"), quoteaf (pretty_filename)); + return false; + } + + *read_pos = pos + bytes_read; + } + while (bytes_read > 0); + + return true; +} + +/* Print the last N_LINES lines from the end of the standard input, + open for reading as pipe FD. + Buffer the text as a linked list of LBUFFERs, adding them as needed. + Return true if successful. */ + +static bool +pipe_lines (char const *pretty_filename, int fd, uintmax_t n_lines, + uintmax_t *read_pos) +{ + struct linebuffer + { + char buffer[BUFSIZ]; + size_t nbytes; + size_t nlines; + struct linebuffer *next; + }; + typedef struct linebuffer LBUFFER; + LBUFFER *first, *last, *tmp; + size_t total_lines = 0; /* Total number of newlines in all buffers. */ + bool ok = true; + size_t n_read; /* Size in bytes of most recent read */ + + first = last = xmalloc (sizeof (LBUFFER)); + first->nbytes = first->nlines = 0; + first->next = nullptr; + tmp = xmalloc (sizeof (LBUFFER)); + + /* Input is always read into a fresh buffer. */ + while (true) + { + n_read = safe_read (fd, tmp->buffer, BUFSIZ); + if (n_read == 0 || n_read == SAFE_READ_ERROR) + break; + tmp->nbytes = n_read; + *read_pos += n_read; + tmp->nlines = 0; + tmp->next = nullptr; + + /* Count the number of newlines just read. */ + { + char const *buffer_end = tmp->buffer + n_read; + char const *p = tmp->buffer; + while ((p = memchr (p, line_end, buffer_end - p))) + { + ++p; + ++tmp->nlines; + } + } + total_lines += tmp->nlines; + + /* If there is enough room in the last buffer read, just append the new + one to it. This is because when reading from a pipe, 'n_read' can + often be very small. */ + if (tmp->nbytes + last->nbytes < BUFSIZ) + { + memcpy (&last->buffer[last->nbytes], tmp->buffer, tmp->nbytes); + last->nbytes += tmp->nbytes; + last->nlines += tmp->nlines; + } + else + { + /* If there's not enough room, link the new buffer onto the end of + the list, then either free up the oldest buffer for the next + read if that would leave enough lines, or else malloc a new one. + Some compaction mechanism is possible but probably not + worthwhile. */ + last = last->next = tmp; + if (total_lines - first->nlines > n_lines) + { + tmp = first; + total_lines -= first->nlines; + first = first->next; + } + else + tmp = xmalloc (sizeof (LBUFFER)); + } + } + + free (tmp); + + if (n_read == SAFE_READ_ERROR) + { + error (0, errno, _("error reading %s"), quoteaf (pretty_filename)); + ok = false; + goto free_lbuffers; + } + + /* If the file is empty, then bail out. */ + if (last->nbytes == 0) + goto free_lbuffers; + + /* This prevents a core dump when the pipe contains no newlines. */ + if (n_lines == 0) + goto free_lbuffers; + + /* Count the incomplete line on files that don't end with a newline. */ + if (last->buffer[last->nbytes - 1] != line_end) + { + ++last->nlines; + ++total_lines; + } + + /* Run through the list, printing lines. First, skip over unneeded + buffers. */ + for (tmp = first; total_lines - tmp->nlines > n_lines; tmp = tmp->next) + total_lines -= tmp->nlines; + + /* Find the correct beginning, then print the rest of the file. */ + { + char const *beg = tmp->buffer; + char const *buffer_end = tmp->buffer + tmp->nbytes; + if (total_lines > n_lines) + { + /* Skip 'total_lines' - 'n_lines' newlines. We made sure that + 'total_lines' - 'n_lines' <= 'tmp->nlines'. */ + size_t j; + for (j = total_lines - n_lines; j; --j) + { + beg = rawmemchr (beg, line_end); + ++beg; + } + } + + xwrite_stdout (beg, buffer_end - beg); + } + + for (tmp = tmp->next; tmp; tmp = tmp->next) + xwrite_stdout (tmp->buffer, tmp->nbytes); + +free_lbuffers: + while (first) + { + tmp = first->next; + free (first); + first = tmp; + } + return ok; +} + +/* Print the last N_BYTES characters from the end of pipe FD. + This is a stripped down version of pipe_lines. + Return true if successful. */ + +static bool +pipe_bytes (char const *pretty_filename, int fd, uintmax_t n_bytes, + uintmax_t *read_pos) +{ + struct charbuffer + { + char buffer[BUFSIZ]; + size_t nbytes; + struct charbuffer *next; + }; + typedef struct charbuffer CBUFFER; + CBUFFER *first, *last, *tmp; + size_t i; /* Index into buffers. */ + size_t total_bytes = 0; /* Total characters in all buffers. */ + bool ok = true; + size_t n_read; + + first = last = xmalloc (sizeof (CBUFFER)); + first->nbytes = 0; + first->next = nullptr; + tmp = xmalloc (sizeof (CBUFFER)); + + /* Input is always read into a fresh buffer. */ + while (true) + { + n_read = safe_read (fd, tmp->buffer, BUFSIZ); + if (n_read == 0 || n_read == SAFE_READ_ERROR) + break; + *read_pos += n_read; + tmp->nbytes = n_read; + tmp->next = nullptr; + + total_bytes += tmp->nbytes; + /* If there is enough room in the last buffer read, just append the new + one to it. This is because when reading from a pipe, 'nbytes' can + often be very small. */ + if (tmp->nbytes + last->nbytes < BUFSIZ) + { + memcpy (&last->buffer[last->nbytes], tmp->buffer, tmp->nbytes); + last->nbytes += tmp->nbytes; + } + else + { + /* If there's not enough room, link the new buffer onto the end of + the list, then either free up the oldest buffer for the next + read if that would leave enough characters, or else malloc a new + one. Some compaction mechanism is possible but probably not + worthwhile. */ + last = last->next = tmp; + if (total_bytes - first->nbytes > n_bytes) + { + tmp = first; + total_bytes -= first->nbytes; + first = first->next; + } + else + { + tmp = xmalloc (sizeof (CBUFFER)); + } + } + } + + free (tmp); + + if (n_read == SAFE_READ_ERROR) + { + error (0, errno, _("error reading %s"), quoteaf (pretty_filename)); + ok = false; + goto free_cbuffers; + } + + /* Run through the list, printing characters. First, skip over unneeded + buffers. */ + for (tmp = first; total_bytes - tmp->nbytes > n_bytes; tmp = tmp->next) + total_bytes -= tmp->nbytes; + + /* Find the correct beginning, then print the rest of the file. + We made sure that 'total_bytes' - 'n_bytes' <= 'tmp->nbytes'. */ + if (total_bytes > n_bytes) + i = total_bytes - n_bytes; + else + i = 0; + xwrite_stdout (&tmp->buffer[i], tmp->nbytes - i); + + for (tmp = tmp->next; tmp; tmp = tmp->next) + xwrite_stdout (tmp->buffer, tmp->nbytes); + +free_cbuffers: + while (first) + { + tmp = first->next; + free (first); + first = tmp; + } + return ok; +} + +/* Skip N_BYTES characters from the start of pipe FD, and print + any extra characters that were read beyond that. + Return 1 on error, 0 if ok, -1 if EOF. */ + +static int +start_bytes (char const *pretty_filename, int fd, uintmax_t n_bytes, + uintmax_t *read_pos) +{ + char buffer[BUFSIZ]; + + while (0 < n_bytes) + { + size_t bytes_read = safe_read (fd, buffer, BUFSIZ); + if (bytes_read == 0) + return -1; + if (bytes_read == SAFE_READ_ERROR) + { + error (0, errno, _("error reading %s"), quoteaf (pretty_filename)); + return 1; + } + *read_pos += bytes_read; + if (bytes_read <= n_bytes) + n_bytes -= bytes_read; + else + { + size_t n_remaining = bytes_read - n_bytes; + /* Print extra characters if there are any. */ + xwrite_stdout (&buffer[n_bytes], n_remaining); + break; + } + } + + return 0; +} + +/* Skip N_LINES lines at the start of file or pipe FD, and print + any extra characters that were read beyond that. + Return 1 on error, 0 if ok, -1 if EOF. */ + +static int +start_lines (char const *pretty_filename, int fd, uintmax_t n_lines, + uintmax_t *read_pos) +{ + if (n_lines == 0) + return 0; + + while (true) + { + char buffer[BUFSIZ]; + size_t bytes_read = safe_read (fd, buffer, BUFSIZ); + if (bytes_read == 0) /* EOF */ + return -1; + if (bytes_read == SAFE_READ_ERROR) /* error */ + { + error (0, errno, _("error reading %s"), quoteaf (pretty_filename)); + return 1; + } + + char *buffer_end = buffer + bytes_read; + + *read_pos += bytes_read; + + char *p = buffer; + while ((p = memchr (p, line_end, buffer_end - p))) + { + ++p; + if (--n_lines == 0) + { + if (p < buffer_end) + xwrite_stdout (p, buffer_end - p); + return 0; + } + } + } +} + +/* Return false when FD is open on a file residing on a local file system. + If fstatfs fails, give a diagnostic and return true. + If fstatfs cannot be called, return true. */ +static bool +fremote (int fd, char const *name) +{ + bool remote = true; /* be conservative (poll by default). */ + +#if HAVE_FSTATFS && HAVE_STRUCT_STATFS_F_TYPE \ + && (defined __linux__ || defined __ANDROID__) + struct statfs buf; + int err = fstatfs (fd, &buf); + if (err != 0) + { + /* On at least linux-2.6.38, fstatfs fails with ENOSYS when FD + is open on a pipe. Treat that like a remote file. */ + if (errno != ENOSYS) + error (0, errno, _("cannot determine location of %s. " + "reverting to polling"), quoteaf (name)); + } + else + { + /* Treat unrecognized file systems as "remote", so caller polls. + Note README-release has instructions for syncing the internal + list with the latest Linux kernel file system constants. */ + remote = is_local_fs_type (buf.f_type) <= 0; + } +#endif + + return remote; +} + +/* open/fstat F->name and handle changes. */ +static void +recheck (struct File_spec *f, bool blocking) +{ + struct stat new_stats; + bool ok = true; + bool is_stdin = (STREQ (f->name, "-")); + bool was_tailable = f->tailable; + int prev_errnum = f->errnum; + bool new_file; + int fd = (is_stdin + ? STDIN_FILENO + : open (f->name, O_RDONLY | (blocking ? 0 : O_NONBLOCK))); + + affirm (valid_file_spec (f)); + + /* If the open fails because the file doesn't exist, + then mark the file as not tailable. */ + f->tailable = !(reopen_inaccessible_files && fd == -1); + + if (! disable_inotify && ! lstat (f->name, &new_stats) + && S_ISLNK (new_stats.st_mode)) + { + /* Diagnose the edge case where a regular file is changed + to a symlink. We avoid inotify with symlinks since + it's awkward to match between symlink name and target. */ + ok = false; + f->errnum = -1; + f->ignore = true; + + error (0, 0, _("%s has been replaced with an untailable symbolic link"), + quoteaf (pretty_name (f))); + } + else if (fd == -1 || fstat (fd, &new_stats) < 0) + { + ok = false; + f->errnum = errno; + if (!f->tailable) + { + if (was_tailable) + { + /* FIXME-maybe: detect the case in which the file first becomes + unreadable (perms), and later becomes readable again and can + be seen to be the same file (dev/ino). Otherwise, tail prints + the entire contents of the file when it becomes readable. */ + error (0, f->errnum, _("%s has become inaccessible"), + quoteaf (pretty_name (f))); + } + else + { + /* say nothing... it's still not tailable */ + } + } + else if (prev_errnum != errno) + error (0, errno, "%s", quotef (pretty_name (f))); + } + else if (!IS_TAILABLE_FILE_TYPE (new_stats.st_mode)) + { + ok = false; + f->errnum = -1; + f->tailable = false; + f->ignore = ! (reopen_inaccessible_files && follow_mode == Follow_name); + if (was_tailable || prev_errnum != f->errnum) + error (0, 0, _("%s has been replaced with an untailable file%s"), + quoteaf (pretty_name (f)), + f->ignore ? _("; giving up on this name") : ""); + } + else if ((f->remote = fremote (fd, pretty_name (f))) && ! disable_inotify) + { + ok = false; + f->errnum = -1; + error (0, 0, _("%s has been replaced with an untailable remote file"), + quoteaf (pretty_name (f))); + f->ignore = true; + f->remote = true; + } + else + { + f->errnum = 0; + } + + new_file = false; + if (!ok) + { + close_fd (fd, pretty_name (f)); + close_fd (f->fd, pretty_name (f)); + f->fd = -1; + } + else if (prev_errnum && prev_errnum != ENOENT) + { + new_file = true; + affirm (f->fd == -1); + error (0, 0, _("%s has become accessible"), quoteaf (pretty_name (f))); + } + else if (f->fd == -1) + { + /* A new file even when inodes haven't changed as <dev,inode> + pairs can be reused, and we know the file was missing + on the previous iteration. Note this also means the file + is redisplayed in --follow=name mode if renamed away from + and back to a monitored name. */ + new_file = true; + + error (0, 0, + _("%s has appeared; following new file"), + quoteaf (pretty_name (f))); + } + else if (f->ino != new_stats.st_ino || f->dev != new_stats.st_dev) + { + /* File has been replaced (e.g., via log rotation) -- + tail the new one. */ + new_file = true; + + error (0, 0, + _("%s has been replaced; following new file"), + quoteaf (pretty_name (f))); + + /* Close the old one. */ + close_fd (f->fd, pretty_name (f)); + + } + else + { + /* No changes detected, so close new fd. */ + close_fd (fd, pretty_name (f)); + } + + /* FIXME: When a log is rotated, daemons tend to log to the + old file descriptor until the new file is present and + the daemon is sent a signal. Therefore tail may miss entries + being written to the old file. Perhaps we should keep + the older file open and continue to monitor it until + data is written to a new file. */ + if (new_file) + { + /* Start at the beginning of the file. */ + record_open_fd (f, fd, 0, &new_stats, (is_stdin ? -1 : blocking)); + if (S_ISREG (new_stats.st_mode)) + xlseek (fd, 0, SEEK_SET, pretty_name (f)); + } +} + +/* Return true if any of the N_FILES files in F are live, i.e., have + open file descriptors, or should be checked again (see --retry). + When following descriptors, checking should only continue when any + of the files is not yet ignored. */ + +static bool +any_live_files (const struct File_spec *f, size_t n_files) +{ + /* In inotify mode, ignore may be set for files + which may later be replaced with new files. + So always consider files live in -F mode. */ + if (reopen_inaccessible_files && follow_mode == Follow_name) + return true; + + for (size_t i = 0; i < n_files; i++) + { + if (0 <= f[i].fd) + return true; + else + { + if (! f[i].ignore && reopen_inaccessible_files) + return true; + } + } + + return false; +} + +/* Tail N_FILES files forever, or until killed. + The pertinent information for each file is stored in an entry of F. + Loop over each of them, doing an fstat to see if they have changed size, + and an occasional open/fstat to see if any dev/ino pair has changed. + If none of them have changed size in one iteration, sleep for a + while and try again. Continue until the user interrupts us. */ + +static void +tail_forever (struct File_spec *f, size_t n_files, double sleep_interval) +{ + /* Use blocking I/O as an optimization, when it's easy. */ + bool blocking = (pid == 0 && follow_mode == Follow_descriptor + && n_files == 1 && f[0].fd != -1 && ! S_ISREG (f[0].mode)); + size_t last; + bool writer_is_dead = false; + + last = n_files - 1; + + while (true) + { + size_t i; + bool any_input = false; + + for (i = 0; i < n_files; i++) + { + int fd; + char const *name; + mode_t mode; + struct stat stats; + uintmax_t bytes_read; + + if (f[i].ignore) + continue; + + if (f[i].fd < 0) + { + recheck (&f[i], blocking); + continue; + } + + fd = f[i].fd; + name = pretty_name (&f[i]); + mode = f[i].mode; + + if (f[i].blocking != blocking) + { + int old_flags = fcntl (fd, F_GETFL); + int new_flags = old_flags | (blocking ? 0 : O_NONBLOCK); + if (old_flags < 0 + || (new_flags != old_flags + && fcntl (fd, F_SETFL, new_flags) == -1)) + { + /* Don't update f[i].blocking if fcntl fails. */ + if (S_ISREG (f[i].mode) && errno == EPERM) + { + /* This happens when using tail -f on a file with + the append-only attribute. */ + } + else + error (EXIT_FAILURE, errno, + _("%s: cannot change nonblocking mode"), + quotef (name)); + } + else + f[i].blocking = blocking; + } + + bool read_unchanged = false; + if (!f[i].blocking) + { + if (fstat (fd, &stats) != 0) + { + f[i].fd = -1; + f[i].errnum = errno; + error (0, errno, "%s", quotef (name)); + close (fd); /* ignore failure */ + continue; + } + + if (f[i].mode == stats.st_mode + && (! S_ISREG (stats.st_mode) || f[i].size == stats.st_size) + && timespec_cmp (f[i].mtime, get_stat_mtime (&stats)) == 0) + { + if ((max_n_unchanged_stats_between_opens + <= f[i].n_unchanged_stats++) + && follow_mode == Follow_name) + { + recheck (&f[i], f[i].blocking); + f[i].n_unchanged_stats = 0; + } + if (fd != f[i].fd || S_ISREG (stats.st_mode) || 1 < n_files) + continue; + else + read_unchanged = true; + } + + affirm (fd == f[i].fd); + + /* This file has changed. Print out what we can, and + then keep looping. */ + + f[i].mtime = get_stat_mtime (&stats); + f[i].mode = stats.st_mode; + + /* reset counter */ + if (! read_unchanged) + f[i].n_unchanged_stats = 0; + + /* XXX: This is only a heuristic, as the file may have also + been truncated and written to if st_size >= size + (in which case we ignore new data <= size). */ + if (S_ISREG (mode) && stats.st_size < f[i].size) + { + error (0, 0, _("%s: file truncated"), quotef (name)); + /* Assume the file was truncated to 0, + and therefore output all "new" data. */ + xlseek (fd, 0, SEEK_SET, name); + f[i].size = 0; + } + + if (i != last) + { + if (print_headers) + write_header (name); + last = i; + } + } + + /* Don't read more than st_size on networked file systems + because it was seen on glusterfs at least, that st_size + may be smaller than the data read on a _subsequent_ stat call. */ + uintmax_t bytes_to_read; + if (f[i].blocking) + bytes_to_read = COPY_A_BUFFER; + else if (S_ISREG (mode) && f[i].remote) + bytes_to_read = stats.st_size - f[i].size; + else + bytes_to_read = COPY_TO_EOF; + + bytes_read = dump_remainder (false, name, fd, bytes_to_read); + + if (read_unchanged && bytes_read) + f[i].n_unchanged_stats = 0; + + any_input |= (bytes_read != 0); + f[i].size += bytes_read; + } + + if (! any_live_files (f, n_files)) + { + error (0, 0, _("no files remaining")); + break; + } + + if ((!any_input || blocking) && fflush (stdout) != 0) + write_error (); + + check_output_alive (); + + /* If nothing was read, sleep and/or check for dead writers. */ + if (!any_input) + { + if (writer_is_dead) + break; + + /* Once the writer is dead, read the files once more to + avoid a race condition. */ + writer_is_dead = (pid != 0 + && kill (pid, 0) != 0 + /* Handle the case in which you cannot send a + signal to the writer, so kill fails and sets + errno to EPERM. */ + && errno != EPERM); + + if (!writer_is_dead && xnanosleep (sleep_interval)) + error (EXIT_FAILURE, errno, _("cannot read realtime clock")); + + } + } +} + +#if HAVE_INOTIFY + +/* Return true if any of the N_FILES files in F is remote, i.e., has + an open file descriptor and is on a network file system. */ + +static bool +any_remote_file (const struct File_spec *f, size_t n_files) +{ + for (size_t i = 0; i < n_files; i++) + if (0 <= f[i].fd && f[i].remote) + return true; + return false; +} + +/* Return true if any of the N_FILES files in F is non remote, i.e., has + an open file descriptor and is not on a network file system. */ + +static bool +any_non_remote_file (const struct File_spec *f, size_t n_files) +{ + for (size_t i = 0; i < n_files; i++) + if (0 <= f[i].fd && ! f[i].remote) + return true; + return false; +} + +/* Return true if any of the N_FILES files in F is a symlink. + Note we don't worry about the edge case where "-" exists, + since that will have the same consequences for inotify, + which is the only context this function is currently used. */ + +static bool +any_symlinks (const struct File_spec *f, size_t n_files) +{ + struct stat st; + for (size_t i = 0; i < n_files; i++) + if (lstat (f[i].name, &st) == 0 && S_ISLNK (st.st_mode)) + return true; + return false; +} + +/* Return true if any of the N_FILES files in F is not + a regular file or fifo. This is used to avoid adding inotify + watches on a device file for example, which inotify + will accept, but not give any events for. */ + +static bool +any_non_regular_fifo (const struct File_spec *f, size_t n_files) +{ + for (size_t i = 0; i < n_files; i++) + if (0 <= f[i].fd && ! S_ISREG (f[i].mode) && ! S_ISFIFO (f[i].mode)) + return true; + return false; +} + +/* Return true if any of the N_FILES files in F represents + stdin and is tailable. */ + +static bool +tailable_stdin (const struct File_spec *f, size_t n_files) +{ + for (size_t i = 0; i < n_files; i++) + if (!f[i].ignore && STREQ (f[i].name, "-")) + return true; + return false; +} + +static size_t +wd_hasher (const void *entry, size_t tabsize) +{ + const struct File_spec *spec = entry; + return spec->wd % tabsize; +} + +static bool +wd_comparator (const void *e1, const void *e2) +{ + const struct File_spec *spec1 = e1; + const struct File_spec *spec2 = e2; + return spec1->wd == spec2->wd; +} + +/* Output (new) data for FSPEC->fd. + PREV_FSPEC records the last File_spec for which we output. */ +static void +check_fspec (struct File_spec *fspec, struct File_spec **prev_fspec) +{ + struct stat stats; + char const *name; + + if (fspec->fd == -1) + return; + + name = pretty_name (fspec); + + if (fstat (fspec->fd, &stats) != 0) + { + fspec->errnum = errno; + close_fd (fspec->fd, name); + fspec->fd = -1; + return; + } + + /* XXX: This is only a heuristic, as the file may have also + been truncated and written to if st_size >= size + (in which case we ignore new data <= size). + Though in the inotify case it's more likely we'll get + separate events for truncate() and write(). */ + if (S_ISREG (fspec->mode) && stats.st_size < fspec->size) + { + error (0, 0, _("%s: file truncated"), quotef (name)); + xlseek (fspec->fd, 0, SEEK_SET, name); + fspec->size = 0; + } + else if (S_ISREG (fspec->mode) && stats.st_size == fspec->size + && timespec_cmp (fspec->mtime, get_stat_mtime (&stats)) == 0) + return; + + bool want_header = print_headers && (fspec != *prev_fspec); + + uintmax_t bytes_read = dump_remainder (want_header, name, fspec->fd, + COPY_TO_EOF); + fspec->size += bytes_read; + + if (bytes_read) + { + *prev_fspec = fspec; + if (fflush (stdout) != 0) + write_error (); + } +} + +/* Attempt to tail N_FILES files forever, or until killed. + Check modifications using the inotify events system. + Exit if finished or on fatal error; return to revert to polling. */ +static void +tail_forever_inotify (int wd, struct File_spec *f, size_t n_files, + double sleep_interval, Hash_table **wd_to_namep) +{ +# if TAIL_TEST_SLEEP + /* Delay between open() and inotify_add_watch() + to help trigger different cases. */ + xnanosleep (1000000); +# endif + unsigned int max_realloc = 3; + + /* Map an inotify watch descriptor to the name of the file it's watching. */ + Hash_table *wd_to_name; + + bool found_watchable_file = false; + bool tailed_but_unwatchable = false; + bool found_unwatchable_dir = false; + bool no_inotify_resources = false; + bool writer_is_dead = false; + struct File_spec *prev_fspec; + size_t evlen = 0; + char *evbuf; + size_t evbuf_off = 0; + size_t len = 0; + + wd_to_name = hash_initialize (n_files, nullptr, wd_hasher, wd_comparator, + nullptr); + if (! wd_to_name) + xalloc_die (); + *wd_to_namep = wd_to_name; + + /* The events mask used with inotify on files (not directories). */ + uint32_t inotify_wd_mask = IN_MODIFY; + /* TODO: Perhaps monitor these events in Follow_descriptor mode also, + to tag reported file names with "deleted", "moved" etc. */ + if (follow_mode == Follow_name) + inotify_wd_mask |= (IN_ATTRIB | IN_DELETE_SELF | IN_MOVE_SELF); + + /* Add an inotify watch for each watched file. If -F is specified then watch + its parent directory too, in this way when they re-appear we can add them + again to the watch list. */ + size_t i; + for (i = 0; i < n_files; i++) + { + if (!f[i].ignore) + { + size_t fnlen = strlen (f[i].name); + if (evlen < fnlen) + evlen = fnlen; + + f[i].wd = -1; + + if (follow_mode == Follow_name) + { + size_t dirlen = dir_len (f[i].name); + char prev = f[i].name[dirlen]; + f[i].basename_start = last_component (f[i].name) - f[i].name; + + f[i].name[dirlen] = '\0'; + + /* It's fine to add the same directory more than once. + In that case the same watch descriptor is returned. */ + f[i].parent_wd = inotify_add_watch (wd, dirlen ? f[i].name : ".", + (IN_CREATE | IN_DELETE + | IN_MOVED_TO | IN_ATTRIB + | IN_DELETE_SELF)); + + f[i].name[dirlen] = prev; + + if (f[i].parent_wd < 0) + { + if (errno != ENOSPC) /* suppress confusing error. */ + error (0, errno, _("cannot watch parent directory of %s"), + quoteaf (f[i].name)); + else + error (0, 0, _("inotify resources exhausted")); + found_unwatchable_dir = true; + /* We revert to polling below. Note invalid uses + of the inotify API will still be diagnosed. */ + break; + } + } + + f[i].wd = inotify_add_watch (wd, f[i].name, inotify_wd_mask); + + if (f[i].wd < 0) + { + if (f[i].fd != -1) /* already tailed. */ + tailed_but_unwatchable = true; + if (errno == ENOSPC || errno == ENOMEM) + { + no_inotify_resources = true; + error (0, 0, _("inotify resources exhausted")); + break; + } + else if (errno != f[i].errnum) + error (0, errno, _("cannot watch %s"), quoteaf (f[i].name)); + continue; + } + + if (hash_insert (wd_to_name, &(f[i])) == nullptr) + xalloc_die (); + + found_watchable_file = true; + } + } + + /* Linux kernel 2.6.24 at least has a bug where eventually, ENOSPC is always + returned by inotify_add_watch. In any case we should revert to polling + when there are no inotify resources. Also a specified directory may not + be currently present or accessible, so revert to polling. Also an already + tailed but unwatchable due rename/unlink race, should also revert. */ + if (no_inotify_resources || found_unwatchable_dir + || (follow_mode == Follow_descriptor && tailed_but_unwatchable)) + return; + if (follow_mode == Follow_descriptor && !found_watchable_file) + exit (EXIT_FAILURE); + + prev_fspec = &(f[n_files - 1]); + + /* Check files again. New files or data can be available since last time we + checked and before they are watched by inotify. */ + for (i = 0; i < n_files; i++) + { + if (! f[i].ignore) + { + /* check for new files. */ + if (follow_mode == Follow_name) + recheck (&(f[i]), false); + else if (f[i].fd != -1) + { + /* If the file was replaced in the small window since we tailed, + then assume the watch is on the wrong item (different to + that we've already produced output for), and so revert to + polling the original descriptor. */ + struct stat stats; + + if (stat (f[i].name, &stats) == 0 + && (f[i].dev != stats.st_dev || f[i].ino != stats.st_ino)) + { + error (0, errno, _("%s was replaced"), + quoteaf (pretty_name (&(f[i])))); + return; + } + } + + /* check for new data. */ + check_fspec (&f[i], &prev_fspec); + } + } + + evlen += sizeof (struct inotify_event) + 1; + evbuf = xmalloc (evlen); + + /* Wait for inotify events and handle them. Events on directories + ensure that watched files can be re-added when following by name. + This loop blocks on the 'safe_read' call until a new event is notified. + But when --pid=P is specified, tail usually waits via poll. */ + while (true) + { + struct File_spec *fspec; + struct inotify_event *ev; + void *void_ev; + + /* When following by name without --retry, and the last file has + been unlinked or renamed-away, diagnose it and return. */ + if (follow_mode == Follow_name + && ! reopen_inaccessible_files + && hash_get_n_entries (wd_to_name) == 0) + error (EXIT_FAILURE, 0, _("no files remaining")); + + if (len <= evbuf_off) + { + /* Poll for inotify events. When watching a PID, ensure + that a read from WD will not block indefinitely. + If MONITOR_OUTPUT, also poll for a broken output pipe. */ + + int file_change; + struct pollfd pfd[2]; + do + { + /* How many ms to wait for changes. -1 means wait forever. */ + int delay = -1; + + if (pid) + { + if (writer_is_dead) + exit (EXIT_SUCCESS); + + writer_is_dead = (kill (pid, 0) != 0 && errno != EPERM); + + if (writer_is_dead || sleep_interval <= 0) + delay = 0; + else if (sleep_interval < INT_MAX / 1000 - 1) + { + /* delay = ceil (sleep_interval * 1000), sans libm. */ + double ddelay = sleep_interval * 1000; + delay = ddelay; + delay += delay < ddelay; + } + } + + pfd[0].fd = wd; + pfd[0].events = POLLIN; + pfd[1].fd = STDOUT_FILENO; + pfd[1].events = pfd[1].revents = 0; + file_change = poll (pfd, monitor_output + 1, delay); + } + while (file_change == 0); + + if (file_change < 0) + error (EXIT_FAILURE, errno, + _("error waiting for inotify and output events")); + if (pfd[1].revents) + die_pipe (); + + len = safe_read (wd, evbuf, evlen); + evbuf_off = 0; + + /* For kernels prior to 2.6.21, read returns 0 when the buffer + is too small. */ + if ((len == 0 || (len == SAFE_READ_ERROR && errno == EINVAL)) + && max_realloc--) + { + len = 0; + evlen *= 2; + evbuf = xrealloc (evbuf, evlen); + continue; + } + + if (len == 0 || len == SAFE_READ_ERROR) + error (EXIT_FAILURE, errno, _("error reading inotify event")); + } + + void_ev = evbuf + evbuf_off; + ev = void_ev; + evbuf_off += sizeof (*ev) + ev->len; + + /* If a directory is deleted, IN_DELETE_SELF is emitted + with ev->name of length 0. + We need to catch it, otherwise it would wait forever, + as wd for directory becomes inactive. Revert to polling now. */ + if ((ev->mask & IN_DELETE_SELF) && ! ev->len) + { + for (i = 0; i < n_files; i++) + { + if (ev->wd == f[i].parent_wd) + { + error (0, 0, + _("directory containing watched file was removed")); + return; + } + } + } + + if (ev->len) /* event on ev->name in watched directory. */ + { + size_t j; + for (j = 0; j < n_files; j++) + { + /* With N=hundreds of frequently-changing files, this O(N^2) + process might be a problem. FIXME: use a hash table? */ + if (f[j].parent_wd == ev->wd + && STREQ (ev->name, f[j].name + f[j].basename_start)) + break; + } + + /* It is not a watched file. */ + if (j == n_files) + continue; + + fspec = &(f[j]); + + int new_wd = -1; + bool deleting = !! (ev->mask & IN_DELETE); + + if (! deleting) + { + /* Adding the same inode again will look up any existing wd. */ + new_wd = inotify_add_watch (wd, f[j].name, inotify_wd_mask); + } + + if (! deleting && new_wd < 0) + { + if (errno == ENOSPC || errno == ENOMEM) + { + error (0, 0, _("inotify resources exhausted")); + return; /* revert to polling. */ + } + else + { + /* Can get ENOENT for a dangling symlink for example. */ + error (0, errno, _("cannot watch %s"), quoteaf (f[j].name)); + } + /* We'll continue below after removing the existing watch. */ + } + + /* This will be false if only attributes of file change. */ + bool new_watch; + new_watch = (! deleting) && (fspec->wd < 0 || new_wd != fspec->wd); + + if (new_watch) + { + if (0 <= fspec->wd) + { + inotify_rm_watch (wd, fspec->wd); + hash_remove (wd_to_name, fspec); + } + + fspec->wd = new_wd; + + if (new_wd == -1) + continue; + + /* If the file was moved then inotify will use the source file wd + for the destination file. Make sure the key is not present in + the table. */ + struct File_spec *prev = hash_remove (wd_to_name, fspec); + if (prev && prev != fspec) + { + if (follow_mode == Follow_name) + recheck (prev, false); + prev->wd = -1; + close_fd (prev->fd, pretty_name (prev)); + } + + if (hash_insert (wd_to_name, fspec) == nullptr) + xalloc_die (); + } + + if (follow_mode == Follow_name) + recheck (fspec, false); + } + else + { + struct File_spec key; + key.wd = ev->wd; + fspec = hash_lookup (wd_to_name, &key); + } + + if (! fspec) + continue; + + if (ev->mask & (IN_ATTRIB | IN_DELETE | IN_DELETE_SELF | IN_MOVE_SELF)) + { + /* Note for IN_MOVE_SELF (the file we're watching has + been clobbered via a rename) we leave the watch + in place since it may still be part of the set + of watched names. */ + if (ev->mask & IN_DELETE_SELF) + { + inotify_rm_watch (wd, fspec->wd); + hash_remove (wd_to_name, fspec); + } + + /* Note we get IN_ATTRIB for unlink() as st_nlink decrements. + The usual path is a close() done in recheck() triggers + an IN_DELETE_SELF event as the inode is removed. + However sometimes open() will succeed as even though + st_nlink is decremented, the dentry (cache) is not updated. + Thus we depend on the IN_DELETE event on the directory + to trigger processing for the removed file. */ + + recheck (fspec, false); + + continue; + } + check_fspec (fspec, &prev_fspec); + } +} +#endif + +/* Output the last N_BYTES bytes of file FILENAME open for reading in FD. + Return true if successful. */ + +static bool +tail_bytes (char const *pretty_filename, int fd, uintmax_t n_bytes, + uintmax_t *read_pos) +{ + struct stat stats; + + if (fstat (fd, &stats)) + { + error (0, errno, _("cannot fstat %s"), quoteaf (pretty_filename)); + return false; + } + + if (from_start) + { + if (! presume_input_pipe && n_bytes <= OFF_T_MAX + && ((S_ISREG (stats.st_mode) + && xlseek (fd, n_bytes, SEEK_CUR, pretty_filename) >= 0) + || lseek (fd, n_bytes, SEEK_CUR) != -1)) + *read_pos += n_bytes; + else + { + int t = start_bytes (pretty_filename, fd, n_bytes, read_pos); + if (t) + return t < 0; + } + n_bytes = COPY_TO_EOF; + } + else + { + off_t end_pos = -1; + off_t current_pos = -1; + + if (! presume_input_pipe && n_bytes <= OFF_T_MAX) + { + if (usable_st_size (&stats)) + end_pos = stats.st_size; + else if ((current_pos = lseek (fd, -n_bytes, SEEK_END)) != -1) + end_pos = current_pos + n_bytes; + } + if (end_pos <= (off_t) ST_BLKSIZE (stats)) + return pipe_bytes (pretty_filename, fd, n_bytes, read_pos); + if (current_pos == -1) + current_pos = xlseek (fd, 0, SEEK_CUR, pretty_filename); + if (current_pos < end_pos) + { + off_t bytes_remaining = end_pos - current_pos; + + if (n_bytes < bytes_remaining) + { + current_pos = end_pos - n_bytes; + xlseek (fd, current_pos, SEEK_SET, pretty_filename); + } + } + *read_pos = current_pos; + } + + *read_pos += dump_remainder (false, pretty_filename, fd, n_bytes); + return true; +} + +/* Output the last N_LINES lines of file FILENAME open for reading in FD. + Return true if successful. */ + +static bool +tail_lines (char const *pretty_filename, int fd, uintmax_t n_lines, + uintmax_t *read_pos) +{ + struct stat stats; + + if (fstat (fd, &stats)) + { + error (0, errno, _("cannot fstat %s"), quoteaf (pretty_filename)); + return false; + } + + if (from_start) + { + int t = start_lines (pretty_filename, fd, n_lines, read_pos); + if (t) + return t < 0; + *read_pos += dump_remainder (false, pretty_filename, fd, COPY_TO_EOF); + } + else + { + off_t start_pos = -1; + off_t end_pos; + + /* Use file_lines only if FD refers to a regular file for + which lseek (... SEEK_END) works. */ + if ( ! presume_input_pipe + && S_ISREG (stats.st_mode) + && (start_pos = lseek (fd, 0, SEEK_CUR)) != -1 + && start_pos < (end_pos = lseek (fd, 0, SEEK_END))) + { + *read_pos = end_pos; + if (end_pos != 0 + && ! file_lines (pretty_filename, fd, n_lines, + start_pos, end_pos, read_pos)) + return false; + } + else + { + /* Under very unlikely circumstances, it is possible to reach + this point after positioning the file pointer to end of file + via the 'lseek (...SEEK_END)' above. In that case, reposition + the file pointer back to start_pos before calling pipe_lines. */ + if (start_pos != -1) + xlseek (fd, start_pos, SEEK_SET, pretty_filename); + + return pipe_lines (pretty_filename, fd, n_lines, read_pos); + } + } + return true; +} + +/* Display the last N_UNITS units of file FILENAME, open for reading + via FD. Set *READ_POS to the position of the input stream pointer. + *READ_POS is usually the number of bytes read and corresponds to an + offset from the beginning of a file. However, it may be larger than + OFF_T_MAX (as for an input pipe), and may also be larger than the + number of bytes read (when an input pointer is initially not at + beginning of file), and may be far greater than the number of bytes + actually read for an input file that is seekable. + Return true if successful. */ + +static bool +tail (char const *filename, int fd, uintmax_t n_units, + uintmax_t *read_pos) +{ + *read_pos = 0; + if (count_lines) + return tail_lines (filename, fd, n_units, read_pos); + else + return tail_bytes (filename, fd, n_units, read_pos); +} + +/* Display the last N_UNITS units of the file described by F. + Return true if successful. */ + +static bool +tail_file (struct File_spec *f, uintmax_t n_units) +{ + int fd; + bool ok; + + bool is_stdin = (STREQ (f->name, "-")); + + if (is_stdin) + { + have_read_stdin = true; + fd = STDIN_FILENO; + xset_binary_mode (STDIN_FILENO, O_BINARY); + } + else + fd = open (f->name, O_RDONLY | O_BINARY); + + f->tailable = !(reopen_inaccessible_files && fd == -1); + + if (fd == -1) + { + if (forever) + { + f->fd = -1; + f->errnum = errno; + f->ignore = ! reopen_inaccessible_files; + f->ino = 0; + f->dev = 0; + } + error (0, errno, _("cannot open %s for reading"), + quoteaf (pretty_name (f))); + ok = false; + } + else + { + uintmax_t read_pos; + + if (print_headers) + write_header (pretty_name (f)); + ok = tail (pretty_name (f), fd, n_units, &read_pos); + if (forever) + { + struct stat stats; + +#if TAIL_TEST_SLEEP + /* Before the tail function provided 'read_pos', there was + a race condition described in the URL below. This sleep + call made the window big enough to exercise the problem. */ + xnanosleep (1); +#endif + f->errnum = ok - 1; + if (fstat (fd, &stats) < 0) + { + ok = false; + f->errnum = errno; + error (0, errno, _("error reading %s"), + quoteaf (pretty_name (f))); + } + else if (!IS_TAILABLE_FILE_TYPE (stats.st_mode)) + { + ok = false; + f->errnum = -1; + f->tailable = false; + f->ignore = ! reopen_inaccessible_files; + error (0, 0, _("%s: cannot follow end of this type of file%s"), + quotef (pretty_name (f)), + f->ignore ? _("; giving up on this name") : ""); + } + + if (!ok) + { + f->ignore = ! reopen_inaccessible_files; + close_fd (fd, pretty_name (f)); + f->fd = -1; + } + else + { + /* Note: we must use read_pos here, not stats.st_size, + to avoid a race condition described by Ken Raeburn: + https://lists.gnu.org/r/bug-textutils/2003-05/msg00007.html */ + record_open_fd (f, fd, read_pos, &stats, (is_stdin ? -1 : 1)); + f->remote = fremote (fd, pretty_name (f)); + } + } + else + { + if (!is_stdin && close (fd)) + { + error (0, errno, _("error reading %s"), + quoteaf (pretty_name (f))); + ok = false; + } + } + } + + return ok; +} + +/* If obsolete usage is allowed, and the command line arguments are of + the obsolete form and the option string is well-formed, set + *N_UNITS, the globals COUNT_LINES, FOREVER, and FROM_START, and + return true. If the command line arguments are obviously incorrect + (e.g., because obsolete usage is not allowed and the arguments are + incorrect for non-obsolete usage), report an error and exit. + Otherwise, return false and don't modify any parameter or global + variable. */ + +static bool +parse_obsolete_option (int argc, char * const *argv, uintmax_t *n_units) +{ + char const *p; + char const *n_string; + char const *n_string_end; + int default_count = DEFAULT_N_LINES; + bool t_from_start; + bool t_count_lines = true; + bool t_forever = false; + + /* With the obsolete form, there is one option string and at most + one file argument. Watch out for "-" and "--", though. */ + if (! (argc == 2 + || (argc == 3 && ! (argv[2][0] == '-' && argv[2][1])) + || (3 <= argc && argc <= 4 && STREQ (argv[2], "--")))) + return false; + + int posix_ver = posix2_version (); + bool obsolete_usage = posix_ver < 200112; + bool traditional_usage = obsolete_usage || 200809 <= posix_ver; + p = argv[1]; + + switch (*p++) + { + default: + return false; + + case '+': + /* Leading "+" is a file name in the standard form. */ + if (!traditional_usage) + return false; + + t_from_start = true; + break; + + case '-': + /* In the non-obsolete form, "-" is standard input and "-c" + requires an option-argument. The obsolete multidigit options + are supported as a GNU extension even when conforming to + POSIX 1003.1-2001 or later, so don't complain about them. */ + if (!obsolete_usage && !p[p[0] == 'c']) + return false; + + t_from_start = false; + break; + } + + n_string = p; + while (ISDIGIT (*p)) + p++; + n_string_end = p; + + switch (*p) + { + case 'b': default_count *= 512; FALLTHROUGH; + case 'c': t_count_lines = false; FALLTHROUGH; + case 'l': p++; break; + } + + if (*p == 'f') + { + t_forever = true; + ++p; + } + + if (*p) + return false; + + if (n_string == n_string_end) + *n_units = default_count; + else if ((xstrtoumax (n_string, nullptr, 10, n_units, "b") + & ~LONGINT_INVALID_SUFFIX_CHAR) + != LONGINT_OK) + error (EXIT_FAILURE, errno, "%s: %s", _("invalid number"), + quote (argv[1])); + + /* Set globals. */ + from_start = t_from_start; + count_lines = t_count_lines; + forever = t_forever; + + return true; +} + +static void +parse_options (int argc, char **argv, + uintmax_t *n_units, enum header_mode *header_mode, + double *sleep_interval) +{ + int c; + + while ((c = getopt_long (argc, argv, "c:n:fFqs:vz0123456789", + long_options, nullptr)) + != -1) + { + switch (c) + { + case 'F': + forever = true; + follow_mode = Follow_name; + reopen_inaccessible_files = true; + break; + + case 'c': + case 'n': + count_lines = (c == 'n'); + if (*optarg == '+') + from_start = true; + else if (*optarg == '-') + ++optarg; + + *n_units = xdectoumax (optarg, 0, UINTMAX_MAX, "bkKmMGTPEZYRQ0", + count_lines + ? _("invalid number of lines") + : _("invalid number of bytes"), 0); + break; + + case 'f': + case LONG_FOLLOW_OPTION: + forever = true; + if (optarg == nullptr) + follow_mode = DEFAULT_FOLLOW_MODE; + else + follow_mode = XARGMATCH ("--follow", optarg, + follow_mode_string, follow_mode_map); + break; + + case RETRY_OPTION: + reopen_inaccessible_files = true; + break; + + case MAX_UNCHANGED_STATS_OPTION: + /* --max-unchanged-stats=N */ + max_n_unchanged_stats_between_opens = + xdectoumax (optarg, 0, UINTMAX_MAX, "", + _("invalid maximum number of unchanged stats between opens"), 0); + break; + + case DISABLE_INOTIFY_OPTION: + disable_inotify = true; + break; + + case PID_OPTION: + pid = xdectoumax (optarg, 0, PID_T_MAX, "", _("invalid PID"), 0); + break; + + case PRESUME_INPUT_PIPE_OPTION: + presume_input_pipe = true; + break; + + case 'q': + *header_mode = never; + break; + + case 's': + { + double s; + if (! (xstrtod (optarg, nullptr, &s, cl_strtod) && 0 <= s)) + error (EXIT_FAILURE, 0, + _("invalid number of seconds: %s"), quote (optarg)); + *sleep_interval = s; + } + break; + + case 'v': + *header_mode = always; + break; + + case 'z': + line_end = '\0'; + break; + + case_GETOPT_HELP_CHAR; + + case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS); + + case '0': case '1': case '2': case '3': case '4': + case '5': case '6': case '7': case '8': case '9': + error (EXIT_FAILURE, 0, _("option used in invalid context -- %c"), c); + + default: + usage (EXIT_FAILURE); + } + } + + if (reopen_inaccessible_files) + { + if (!forever) + { + reopen_inaccessible_files = false; + error (0, 0, _("warning: --retry ignored; --retry is useful" + " only when following")); + } + else if (follow_mode == Follow_descriptor) + error (0, 0, _("warning: --retry only effective for the initial open")); + } + + if (pid && !forever) + error (0, 0, + _("warning: PID ignored; --pid=PID is useful only when following")); + else if (pid && kill (pid, 0) != 0 && errno == ENOSYS) + { + error (0, 0, _("warning: --pid=PID is not supported on this system")); + pid = 0; + } +} + +/* Mark as '.ignore'd each member of F that corresponds to a + pipe or fifo, and return the number of non-ignored members. */ +static size_t +ignore_fifo_and_pipe (struct File_spec *f, size_t n_files) +{ + /* When there is no FILE operand and stdin is a pipe or FIFO + POSIX requires that tail ignore the -f option. + Since we allow multiple FILE operands, we extend that to say: with -f, + ignore any "-" operand that corresponds to a pipe or FIFO. */ + size_t n_viable = 0; + + for (size_t i = 0; i < n_files; i++) + { + bool is_a_fifo_or_pipe = + (STREQ (f[i].name, "-") + && !f[i].ignore + && 0 <= f[i].fd + && (S_ISFIFO (f[i].mode) + || (HAVE_FIFO_PIPES != 1 && isapipe (f[i].fd)))); + if (is_a_fifo_or_pipe) + { + f[i].fd = -1; + f[i].ignore = true; + } + else + ++n_viable; + } + + return n_viable; +} + +int +main (int argc, char **argv) +{ + enum header_mode header_mode = multiple_files; + bool ok = true; + /* If from_start, the number of items to skip before printing; otherwise, + the number of items at the end of the file to print. Although the type + is signed, the value is never negative. */ + uintmax_t n_units = DEFAULT_N_LINES; + size_t n_files; + char **file; + struct File_spec *F; + size_t i; + bool obsolete_option; + + /* The number of seconds to sleep between iterations. + During one iteration, every file name or descriptor is checked to + see if it has changed. */ + double sleep_interval = 1.0; + + initialize_main (&argc, &argv); + set_program_name (argv[0]); + setlocale (LC_ALL, ""); + bindtextdomain (PACKAGE, LOCALEDIR); + textdomain (PACKAGE); + + atexit (close_stdout); + + have_read_stdin = false; + + count_lines = true; + forever = from_start = print_headers = false; + line_end = '\n'; + obsolete_option = parse_obsolete_option (argc, argv, &n_units); + argc -= obsolete_option; + argv += obsolete_option; + parse_options (argc, argv, &n_units, &header_mode, &sleep_interval); + + /* To start printing with item N_UNITS from the start of the file, skip + N_UNITS - 1 items. 'tail -n +0' is actually meaningless, but for Unix + compatibility it's treated the same as 'tail -n +1'. */ + if (from_start) + { + if (n_units) + --n_units; + } + + if (optind < argc) + { + n_files = argc - optind; + file = argv + optind; + } + else + { + static char *dummy_stdin = (char *) "-"; + n_files = 1; + file = &dummy_stdin; + } + + { + bool found_hyphen = false; + + for (i = 0; i < n_files; i++) + if (STREQ (file[i], "-")) + found_hyphen = true; + + /* When following by name, there must be a name. */ + if (found_hyphen && follow_mode == Follow_name) + error (EXIT_FAILURE, 0, _("cannot follow %s by name"), quoteaf ("-")); + + /* When following forever, and not using simple blocking, warn if + any file is '-' as the stats() used to check for input are ineffective. + This is only a warning, since tail's output (before a failing seek, + and that from any non-stdin files) might still be useful. */ + if (forever && found_hyphen) + { + struct stat in_stat; + bool blocking_stdin; + blocking_stdin = (pid == 0 && follow_mode == Follow_descriptor + && n_files == 1 && ! fstat (STDIN_FILENO, &in_stat) + && ! S_ISREG (in_stat.st_mode)); + + if (! blocking_stdin && isatty (STDIN_FILENO)) + error (0, 0, _("warning: following standard input" + " indefinitely is ineffective")); + } + } + + /* Don't read anything if we'll never output anything. */ + if (! n_units && ! forever && ! from_start) + return EXIT_SUCCESS; + + F = xnmalloc (n_files, sizeof *F); + for (i = 0; i < n_files; i++) + F[i].name = file[i]; + + if (header_mode == always + || (header_mode == multiple_files && n_files > 1)) + print_headers = true; + + xset_binary_mode (STDOUT_FILENO, O_BINARY); + + for (i = 0; i < n_files; i++) + ok &= tail_file (&F[i], n_units); + + if (forever && ignore_fifo_and_pipe (F, n_files)) + { + /* If stdout is a fifo or pipe, then monitor it + so that we exit if the reader goes away. */ + struct stat out_stat; + if (fstat (STDOUT_FILENO, &out_stat) < 0) + error (EXIT_FAILURE, errno, _("standard output")); + monitor_output = (S_ISFIFO (out_stat.st_mode) + || (HAVE_FIFO_PIPES != 1 && isapipe (STDOUT_FILENO))); + +#if HAVE_INOTIFY + /* tailable_stdin() checks if the user specifies stdin via "-", + or implicitly by providing no arguments. If so, we won't use inotify. + Technically, on systems with a working /dev/stdin, we *could*, + but would it be worth it? Verifying that it's a real device + and hooked up to stdin is not trivial, while reverting to + non-inotify-based tail_forever is easy and portable. + + any_remote_file() checks if the user has specified any + files that reside on remote file systems. inotify is not used + in this case because it would miss any updates to the file + that were not initiated from the local system. + + any_non_remote_file() checks if the user has specified any + files that don't reside on remote file systems. inotify is not used + if there are no open files, as we can't determine if those file + will be on a remote file system. + + any_symlinks() checks if the user has specified any symbolic links. + inotify is not used in this case because it returns updated _targets_ + which would not match the specified names. If we tried to always + use the target names, then we would miss changes to the symlink itself. + + ok is false when one of the files specified could not be opened for + reading. In this case and when following by descriptor, + tail_forever_inotify() cannot be used (in its current implementation). + + FIXME: inotify doesn't give any notification when a new + (remote) file or directory is mounted on top a watched file. + When follow_mode == Follow_name we would ideally like to detect that. + Note if there is a change to the original file then we'll + recheck it and follow the new file, or ignore it if the + file has changed to being remote. + + FIXME-maybe: inotify has a watch descriptor per inode, and hence with + our current hash implementation will only --follow data for one + of the names when multiple hardlinked files are specified, or + for one name when a name is specified multiple times. */ + if (!disable_inotify && (tailable_stdin (F, n_files) + || any_remote_file (F, n_files) + || ! any_non_remote_file (F, n_files) + || any_symlinks (F, n_files) + || any_non_regular_fifo (F, n_files) + || (!ok && follow_mode == Follow_descriptor))) + disable_inotify = true; + + if (!disable_inotify) + { + int wd = inotify_init (); + if (0 <= wd) + { + /* Flush any output from tail_file, now, since + tail_forever_inotify flushes only after writing, + not before reading. */ + if (fflush (stdout) != 0) + write_error (); + + Hash_table *ht; + tail_forever_inotify (wd, F, n_files, sleep_interval, &ht); + hash_free (ht); + close (wd); + errno = 0; + } + error (0, errno, _("inotify cannot be used, reverting to polling")); + } +#endif + disable_inotify = true; + tail_forever (F, n_files, sleep_interval); + } + + if (have_read_stdin && close (STDIN_FILENO) < 0) + error (EXIT_FAILURE, errno, "-"); + main_exit (ok ? EXIT_SUCCESS : EXIT_FAILURE); +} |