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Diffstat (limited to 'common/dotlock.c')
| -rw-r--r-- | common/dotlock.c | 1443 |
1 files changed, 1443 insertions, 0 deletions
diff --git a/common/dotlock.c b/common/dotlock.c new file mode 100644 index 0000000..772bda3 --- /dev/null +++ b/common/dotlock.c @@ -0,0 +1,1443 @@ +/* dotlock.c - dotfile locking + * Copyright (C) 1998, 2000, 2001, 2003, 2004, + * 2005, 2006, 2008, 2010, 2011 Free Software Foundation, Inc. + * + * This file is part of GnuPG. + * + * GnuPG is free software; you can redistribute and/or modify this + * part of GnuPG under the terms of either + * + * - the GNU Lesser General Public License as published by the Free + * Software Foundation; either version 3 of the License, or (at + * your option) any later version. + * + * or + * + * - the GNU General Public License as published by the Free + * Software Foundation; either version 2 of the License, or (at + * your option) any later version. + * + * or both in parallel, as here. + * + * GnuPG 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 copies of the GNU General Public License + * and the GNU Lesser General Public License along with this program; + * if not, see <https://www.gnu.org/licenses/>. + * + * ALTERNATIVELY, this file may be distributed under the terms of the + * following license, in which case the provisions of this license are + * required INSTEAD OF the GNU Lesser General License or the GNU + * General Public License. If you wish to allow use of your version of + * this file only under the terms of the GNU Lesser General License or + * the GNU General Public License, and not to allow others to use your + * version of this file under the terms of the following license, + * indicate your decision by deleting this paragraph and the license + * below. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * + * 1. Redistributions of source code must retain the above copyright + * notice, and the entire permission notice in its entirety, + * including the disclaimer of warranties. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * 3. The name of the author may not be used to endorse or promote + * products derived from this software without specific prior + * written permission. + * + * THIS SOFTWARE IS PROVIDED "AS IS" AND ANY EXPRESS OR IMPLIED + * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES + * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE + * DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, + * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES + * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR + * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, + * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) + * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED + * OF THE POSSIBILITY OF SUCH DAMAGE. + */ + +/* + Overview: + ========= + + This module implements advisory file locking in a portable way. + Due to the problems with POSIX fcntl locking a separate lock file + is used. It would be possible to use fcntl locking on this lock + file and thus avoid the weird auto unlock bug of POSIX while still + having an unproved better performance of fcntl locking. However + there are still problems left, thus we resort to use a hardlink + which has the well defined property that a link call will fail if + the target file already exists. + + Given that hardlinks are also available on NTFS file systems since + Windows XP; it will be possible to enhance this module to use + hardlinks even on Windows and thus allow Windows and Posix clients + to use locking on the same directory. This is not yet implemented; + instead we use a lockfile on Windows along with W32 style file + locking. + + On FAT file systems hardlinks are not supported. Thus this method + does not work. Our solution is to use a O_EXCL locking instead. + Querying the type of the file system is not easy to do in a + portable way (e.g. Linux has a statfs, BSDs have a the same call + but using different structures and constants). What we do instead + is to check at runtime whether link(2) works for a specific lock + file. + + + How to use: + =========== + + At program initialization time, the module should be explicitly + initialized: + + dotlock_create (NULL, 0); + + This installs an atexit handler and may also initialize mutex etc. + It is optional for non-threaded applications. Only the first call + has an effect. This needs to be done before any extra threads are + started. + + To create a lock file (which prepares it but does not take the + lock) you do: + + dotlock_t h + + h = dotlock_create (fname, 0); + if (!h) + error ("error creating lock file: %s\n", strerror (errno)); + + It is important to handle the error. For example on a read-only + file system a lock can't be created (but is usually not needed). + FNAME is the file you want to lock; the actual lockfile is that + name with the suffix ".lock" appended. On success a handle to be + used with the other functions is returned or NULL on error. Note + that the handle shall only be used by one thread at a time. This + function creates a unique file temporary file (".#lk*") in the same + directory as FNAME and returns a handle for further operations. + The module keeps track of these unique files so that they will be + unlinked using the atexit handler. If you don't need the lock file + anymore, you may also explicitly remove it with a call to: + + dotlock_destroy (h); + + To actually lock the file, you use: + + if (dotlock_take (h, -1)) + error ("error taking lock: %s\n", strerror (errno)); + + This function will wait until the lock is acquired. If an + unexpected error occurs if will return non-zero and set ERRNO. If + you pass (0) instead of (-1) the function does not wait in case the + file is already locked but returns -1 and sets ERRNO to EACCES. + Any other positive value for the second parameter is considered a + timeout value in milliseconds. + + To release the lock you call: + + if (dotlock_release (h)) + error ("error releasing lock: %s\n", strerror (errno)); + + or, if the lock file is not anymore needed, you may just call + dotlock_destroy. However dotlock_release does some extra checks + before releasing the lock and prints diagnostics to help detecting + bugs. + + If you want to explicitly destroy all lock files you may call + + dotlock_remove_lockfiles (); + + which is the core of the installed atexit handler. In case your + application wants to disable locking completely it may call + + disable_locking () + + before any locks are created. + + There are two convenience functions to store an integer (e.g. a + file descriptor) value with the handle: + + void dotlock_set_fd (dotlock_t h, int fd); + int dotlock_get_fd (dotlock_t h); + + If nothing has been stored dotlock_get_fd returns -1. + + + + How to build: + ============= + + This module was originally developed for GnuPG but later changed to + allow its use without any GnuPG dependency. If you want to use it + with you application you may simply use it and it should figure out + most things automagically. + + You may use the common config.h file to pass macros, but take care + to pass -DHAVE_CONFIG_H to the compiler. Macros used by this + module are: + + DOTLOCK_USE_PTHREAD - Define if POSIX threads are in use. + + DOTLOCK_GLIB_LOGGING - Define this to use Glib logging functions. + + DOTLOCK_EXT_SYM_PREFIX - Prefix all external symbols with the + string to which this macro evaluates. + + GNUPG_MAJOR_VERSION - Defined when used by GnuPG. + + HAVE_DOSISH_SYSTEM - Defined for Windows etc. Will be + automatically defined if a the target is + Windows. + + HAVE_POSIX_SYSTEM - Internally defined to !HAVE_DOSISH_SYSTEM. + + HAVE_SIGNAL_H - Should be defined on Posix systems. If config.h + is not used defaults to defined. + + DIRSEP_C - Separation character for file name parts. + Usually not redefined. + + EXTSEP_S - Separation string for file name suffixes. + Usually not redefined. + + HAVE_W32CE_SYSTEM - Currently only used by GnuPG. + + Note that there is a test program t-dotlock which has compile + instructions at its end. At least for SMBFS and CIFS it is + important that 64 bit versions of stat are used; most programming + environments do this these days, just in case you want to compile + it on the command line, remember to pass -D_FILE_OFFSET_BITS=64 + + + Bugs: + ===== + + On Windows this module is not yet thread-safe. + + + Miscellaneous notes: + ==================== + + On hardlinks: + - Hardlinks are supported under Windows with NTFS since XP/Server2003. + - In Linux 2.6.33 both SMBFS and CIFS seem to support hardlinks. + - NFS supports hard links. But there are solvable problems. + - FAT does not support links + + On the file locking API: + - CIFS on Linux 2.6.33 supports several locking methods. + SMBFS seems not to support locking. No closer checks done. + - NFS supports Posix locks. flock is emulated in the server. + However there are a couple of problems; see below. + - FAT does not support locks. + - An advantage of fcntl locking is that R/W locks can be + implemented which is not easy with a straight lock file. + + On O_EXCL: + - Does not work reliable on NFS + - Should work on CIFS and SMBFS but how can we delete lockfiles? + + On NFS problems: + - Locks vanish if the server crashes and reboots. + - Client crashes keep the lock in the server until the client + re-connects. + - Communication problems may return unreliable error codes. The + MUA Postfix's workaround is to compare the link count after + seeing an error for link. However that gives a race. If using a + unique file to link to a lockfile and using stat to check the + link count instead of looking at the error return of link(2) is + the best solution. + - O_EXCL seems to have a race and may re-create a file anyway. + +*/ + +#ifdef HAVE_CONFIG_H +# include <config.h> +#endif + +/* Some quick replacements for stuff we usually expect to be defined + in config.h. Define HAVE_POSIX_SYSTEM for better readability. */ +#if !defined (HAVE_DOSISH_SYSTEM) && defined(_WIN32) +# define HAVE_DOSISH_SYSTEM 1 +#endif +#if !defined (HAVE_DOSISH_SYSTEM) && !defined (HAVE_POSIX_SYSTEM) +# define HAVE_POSIX_SYSTEM 1 +#endif + +/* With no config.h assume that we have sitgnal.h. */ +#if !defined (HAVE_CONFIG_H) && defined (HAVE_POSIX_SYSTEM) +# define HAVE_SIGNAL_H 1 +#endif + +/* Standard headers. */ +#include <stdlib.h> +#include <stdio.h> +#include <string.h> +#include <errno.h> +#include <ctype.h> +#include <errno.h> +#include <unistd.h> +#ifdef HAVE_DOSISH_SYSTEM +# define WIN32_LEAN_AND_MEAN /* We only need the OS core stuff. */ +# include <windows.h> +#else +# include <sys/types.h> +# include <sys/stat.h> +# include <sys/utsname.h> +#endif +#include <sys/types.h> +#include <sys/time.h> +#include <sys/stat.h> +#include <fcntl.h> +#ifdef HAVE_SIGNAL_H +# include <signal.h> +#endif +#ifdef DOTLOCK_USE_PTHREAD +# include <pthread.h> +#endif + +#ifdef DOTLOCK_GLIB_LOGGING +# include <glib.h> +#endif + +#ifdef GNUPG_MAJOR_VERSION +# include "util.h" +# include "common-defs.h" +# include "stringhelp.h" /* For stpcpy and w32_strerror. */ +#endif +#ifdef HAVE_W32CE_SYSTEM +# include "utf8conv.h" /* WindowsCE requires filename conversion. */ +#endif + +#include "dotlock.h" + + +/* Define constants for file name construction. */ +#if !defined(DIRSEP_C) && !defined(EXTSEP_S) +# ifdef HAVE_DOSISH_SYSTEM +# define DIRSEP_C '\\' +# define EXTSEP_S "." +#else +# define DIRSEP_C '/' +# define EXTSEP_S "." +# endif +#endif + +/* In GnuPG we use wrappers around the malloc functions. If they are + not defined we assume that this code is used outside of GnuPG and + fall back to the regular malloc functions. */ +#ifndef xtrymalloc +# define xtrymalloc(a) malloc ((a)) +# define xtrycalloc(a,b) calloc ((a), (b)) +# define xfree(a) free ((a)) +#endif + +/* Wrapper to set ERRNO (required for W32CE). */ +#ifdef GPG_ERROR_VERSION +# define my_set_errno(e) gpg_err_set_errno ((e)) +#else +# define my_set_errno(e) do { errno = (e); } while (0) +#endif + +/* Gettext macro replacement. */ +#ifndef _ +# define _(a) (a) +#endif + +#ifdef GNUPG_MAJOR_VERSION +# define my_info_0(a) log_info ((a)) +# define my_info_1(a,b) log_info ((a), (b)) +# define my_info_2(a,b,c) log_info ((a), (b), (c)) +# define my_info_3(a,b,c,d) log_info ((a), (b), (c), (d)) +# define my_error_0(a) log_error ((a)) +# define my_error_1(a,b) log_error ((a), (b)) +# define my_error_2(a,b,c) log_error ((a), (b), (c)) +# define my_debug_1(a,b) log_debug ((a), (b)) +# define my_fatal_0(a) log_fatal ((a)) +#elif defined (DOTLOCK_GLIB_LOGGING) +# define my_info_0(a) g_message ((a)) +# define my_info_1(a,b) g_message ((a), (b)) +# define my_info_2(a,b,c) g_message ((a), (b), (c)) +# define my_info_3(a,b,c,d) g_message ((a), (b), (c), (d)) +# define my_error_0(a) g_warning ((a)) +# define my_error_1(a,b) g_warning ((a), (b)) +# define my_error_2(a,b,c) g_warning ((a), (b), (c)) +# define my_debug_1(a,b) g_debug ((a), (b)) +# define my_fatal_0(a) g_error ((a)) +#else +# define my_info_0(a) fprintf (stderr, (a)) +# define my_info_1(a,b) fprintf (stderr, (a), (b)) +# define my_info_2(a,b,c) fprintf (stderr, (a), (b), (c)) +# define my_info_3(a,b,c,d) fprintf (stderr, (a), (b), (c), (d)) +# define my_error_0(a) fprintf (stderr, (a)) +# define my_error_1(a,b) fprintf (stderr, (a), (b)) +# define my_error_2(a,b,c) fprintf (stderr, (a), (b), (c)) +# define my_debug_1(a,b) fprintf (stderr, (a), (b)) +# define my_fatal_0(a) do { fprintf (stderr,(a)); fflush (stderr); \ + abort (); } while (0) +#endif + + + + + +/* The object describing a lock. */ +struct dotlock_handle +{ + struct dotlock_handle *next; + char *lockname; /* Name of the actual lockfile. */ + unsigned int locked:1; /* Lock status. */ + unsigned int disable:1; /* If true, locking is disabled. */ + unsigned int use_o_excl:1; /* Use open (O_EXCL) for locking. */ + + int extra_fd; /* A place for the caller to store an FD. */ + +#ifdef HAVE_DOSISH_SYSTEM + HANDLE lockhd; /* The W32 handle of the lock file. */ +#else /*!HAVE_DOSISH_SYSTEM */ + char *tname; /* Name of the lockfile template. */ + size_t nodename_off; /* Offset in TNAME of the nodename part. */ + size_t nodename_len; /* Length of the nodename part. */ +#endif /*!HAVE_DOSISH_SYSTEM */ +}; + + +/* A list of all lock handles. The volatile attribute might help + if used in an atexit handler. Note that [UN]LOCK_all_lockfiles + must not change ERRNO. */ +static volatile dotlock_t all_lockfiles; +#ifdef DOTLOCK_USE_PTHREAD +static pthread_mutex_t all_lockfiles_mutex = PTHREAD_MUTEX_INITIALIZER; +# define LOCK_all_lockfiles() do { \ + if (pthread_mutex_lock (&all_lockfiles_mutex)) \ + my_fatal_0 ("locking all_lockfiles_mutex failed\n"); \ + } while (0) +# define UNLOCK_all_lockfiles() do { \ + if (pthread_mutex_unlock (&all_lockfiles_mutex)) \ + my_fatal_0 ("unlocking all_lockfiles_mutex failed\n"); \ + } while (0) +#else /*!DOTLOCK_USE_PTHREAD*/ +# define LOCK_all_lockfiles() do { } while (0) +# define UNLOCK_all_lockfiles() do { } while (0) +#endif /*!DOTLOCK_USE_PTHREAD*/ + +/* If this has the value true all locking is disabled. */ +static int never_lock; + + + + +#ifdef HAVE_DOSISH_SYSTEM +/* FIXME: For use in GnuPG this can be replaced by + * gnupg_w32_set_errno. */ +static int +map_w32_to_errno (DWORD w32_err) +{ + switch (w32_err) + { + case 0: + return 0; + + case ERROR_FILE_NOT_FOUND: + return ENOENT; + + case ERROR_PATH_NOT_FOUND: + return ENOENT; + + case ERROR_ACCESS_DENIED: + return EPERM; + + case ERROR_INVALID_HANDLE: + case ERROR_INVALID_BLOCK: + return EINVAL; + + case ERROR_NOT_ENOUGH_MEMORY: + return ENOMEM; + + case ERROR_NO_DATA: + case ERROR_BROKEN_PIPE: + return EPIPE; + + default: + return EIO; + } +} +#endif /*HAVE_DOSISH_SYSTEM*/ + + +#ifdef HAVE_W32_SYSTEM +static int +any8bitchar (const char *string) +{ + if (string) + for ( ; *string; string++) + if ((*string & 0x80)) + return 1; + return 0; +} +#endif /*HAVE_W32_SYSTEM*/ + + + + +/* Entirely disable all locking. This function should be called + before any locking is done. It may be called right at startup of + the process as it only sets a global value. */ +void +dotlock_disable (void) +{ + never_lock = 1; +} + + +#ifdef HAVE_POSIX_SYSTEM +static int +maybe_deadlock (dotlock_t h) +{ + dotlock_t r; + int res = 0; + + LOCK_all_lockfiles (); + for (r=all_lockfiles; r; r = r->next) + { + if ( r != h && r->locked ) + { + res = 1; + break; + } + } + UNLOCK_all_lockfiles (); + return res; +} +#endif /*HAVE_POSIX_SYSTEM*/ + + +/* Read the lock file and return the pid, returns -1 on error. True + will be stored in the integer at address SAME_NODE if the lock file + has been created on the same node. */ +#ifdef HAVE_POSIX_SYSTEM +static int +read_lockfile (dotlock_t h, int *same_node, int *r_fd) +{ + char buffer_space[10+1+70+1]; /* 70 is just an estimated value; node + names are usually shorter. */ + int fd; + int pid = -1; + char *buffer, *p; + size_t expected_len; + int res, nread; + + *same_node = 0; + expected_len = 10 + 1 + h->nodename_len + 1; + if ( expected_len >= sizeof buffer_space) + { + buffer = xtrymalloc (expected_len); + if (!buffer) + return -1; + } + else + buffer = buffer_space; + + if ( (fd = open (h->lockname, O_RDONLY)) == -1 ) + { + int e = errno; + my_info_2 ("error opening lockfile '%s': %s\n", + h->lockname, strerror(errno) ); + if (buffer != buffer_space) + xfree (buffer); + my_set_errno (e); /* Need to return ERRNO here. */ + return -1; + } + + p = buffer; + nread = 0; + do + { + res = read (fd, p, expected_len - nread); + if (res == -1 && errno == EINTR) + continue; + if (res < 0) + { + int e = errno; + my_info_1 ("error reading lockfile '%s'\n", h->lockname ); + close (fd); + if (buffer != buffer_space) + xfree (buffer); + my_set_errno (e); + return -1; + } + p += res; + nread += res; + } + while (res && nread != expected_len); + + if (r_fd) + *r_fd = fd; + else + close(fd); + + if (nread < 11) + { + my_info_1 ("invalid size of lockfile '%s'\n", h->lockname); + if (buffer != buffer_space) + xfree (buffer); + my_set_errno (EINVAL); + return -1; + } + + if (buffer[10] != '\n' + || (buffer[10] = 0, pid = atoi (buffer)) == -1 + || !pid ) + { + my_error_2 ("invalid pid %d in lockfile '%s'\n", pid, h->lockname); + if (buffer != buffer_space) + xfree (buffer); + my_set_errno (EINVAL); + return -1; + } + + if (nread == expected_len + && !memcmp (h->tname+h->nodename_off, buffer+11, h->nodename_len) + && buffer[11+h->nodename_len] == '\n') + *same_node = 1; + + if (buffer != buffer_space) + xfree (buffer); + return pid; +} +#endif /*HAVE_POSIX_SYSTEM */ + + +/* Check whether the file system which stores TNAME supports + hardlinks. Instead of using the non-portable statsfs call which + differs between various Unix versions, we do a runtime test. + Returns: 0 supports hardlinks; 1 no hardlink support, -1 unknown + (test error). */ +#ifdef HAVE_POSIX_SYSTEM +static int +use_hardlinks_p (const char *tname) +{ + char *lname; + struct stat sb; + unsigned int nlink; + int res; + + if (stat (tname, &sb)) + return -1; + nlink = (unsigned int)sb.st_nlink; + + lname = xtrymalloc (strlen (tname) + 1 + 1); + if (!lname) + return -1; + strcpy (lname, tname); + strcat (lname, "x"); + + /* We ignore the return value of link() because it is unreliable. */ + (void) link (tname, lname); + + if (stat (tname, &sb)) + res = -1; /* Ooops. */ + else if (sb.st_nlink == nlink + 1) + res = 0; /* Yeah, hardlinks are supported. */ + else + res = 1; /* No hardlink support. */ + + unlink (lname); + xfree (lname); + return res; +} +#endif /*HAVE_POSIX_SYSTEM */ + + + +#ifdef HAVE_POSIX_SYSTEM +/* Locking core for Unix. It used a temporary file and the link + system call to make locking an atomic operation. */ +static dotlock_t +dotlock_create_unix (dotlock_t h, const char *file_to_lock) +{ + int fd = -1; + char pidstr[16]; + const char *nodename; + const char *dirpart; + int dirpartlen; + struct utsname utsbuf; + size_t tnamelen; + + snprintf (pidstr, sizeof pidstr, "%10d\n", (int)getpid() ); + + /* Create a temporary file. */ + if ( uname ( &utsbuf ) ) + nodename = "unknown"; + else + nodename = utsbuf.nodename; + + if ( !(dirpart = strrchr (file_to_lock, DIRSEP_C)) ) + { + dirpart = EXTSEP_S; + dirpartlen = 1; + } + else + { + dirpartlen = dirpart - file_to_lock; + dirpart = file_to_lock; + } + + LOCK_all_lockfiles (); + h->next = all_lockfiles; + all_lockfiles = h; + + tnamelen = dirpartlen + 6 + 30 + strlen(nodename) + 10 + 1; + h->tname = xtrymalloc (tnamelen + 1); + if (!h->tname) + { + all_lockfiles = h->next; + UNLOCK_all_lockfiles (); + xfree (h); + return NULL; + } + h->nodename_len = strlen (nodename); + + snprintf (h->tname, tnamelen, "%.*s/.#lk%p.", dirpartlen, dirpart, h ); + h->nodename_off = strlen (h->tname); + snprintf (h->tname+h->nodename_off, tnamelen - h->nodename_off, + "%s.%d", nodename, (int)getpid ()); + + do + { + my_set_errno (0); + fd = open (h->tname, O_WRONLY|O_CREAT|O_EXCL, + S_IRUSR|S_IRGRP|S_IROTH|S_IWUSR ); + } + while (fd == -1 && errno == EINTR); + + if ( fd == -1 ) + { + int saveerrno = errno; + all_lockfiles = h->next; + UNLOCK_all_lockfiles (); + my_error_2 (_("failed to create temporary file '%s': %s\n"), + h->tname, strerror (errno)); + xfree (h->tname); + xfree (h); + my_set_errno (saveerrno); + return NULL; + } + if ( write (fd, pidstr, 11 ) != 11 ) + goto write_failed; + if ( write (fd, nodename, strlen (nodename) ) != strlen (nodename) ) + goto write_failed; + if ( write (fd, "\n", 1 ) != 1 ) + goto write_failed; + if ( close (fd) ) + { + if ( errno == EINTR ) + fd = -1; + goto write_failed; + } + fd = -1; + + /* Check whether we support hard links. */ + switch (use_hardlinks_p (h->tname)) + { + case 0: /* Yes. */ + break; + case 1: /* No. */ + unlink (h->tname); + h->use_o_excl = 1; + break; + default: + { + int saveerrno = errno; + my_error_2 ("can't check whether hardlinks are supported for '%s': %s\n" + , h->tname, strerror (saveerrno)); + my_set_errno (saveerrno); + } + goto write_failed; + } + + h->lockname = xtrymalloc (strlen (file_to_lock) + 6 ); + if (!h->lockname) + { + int saveerrno = errno; + all_lockfiles = h->next; + UNLOCK_all_lockfiles (); + unlink (h->tname); + xfree (h->tname); + xfree (h); + my_set_errno (saveerrno); + return NULL; + } + strcpy (stpcpy (h->lockname, file_to_lock), EXTSEP_S "lock"); + UNLOCK_all_lockfiles (); + + return h; + + write_failed: + { + int saveerrno = errno; + all_lockfiles = h->next; + UNLOCK_all_lockfiles (); + my_error_2 (_("error writing to '%s': %s\n"), h->tname, strerror (errno)); + if ( fd != -1 ) + close (fd); + unlink (h->tname); + xfree (h->tname); + xfree (h); + my_set_errno (saveerrno); + } + return NULL; +} +#endif /*HAVE_POSIX_SYSTEM*/ + + +#ifdef HAVE_DOSISH_SYSTEM +/* Locking core for Windows. This version does not need a temporary + file but uses the plain lock file along with record locking. We + create this file here so that we later only need to do the file + locking. For error reporting it is useful to keep the name of the + file in the handle. */ +static dotlock_t +dotlock_create_w32 (dotlock_t h, const char *file_to_lock) +{ + LOCK_all_lockfiles (); + h->next = all_lockfiles; + all_lockfiles = h; + + h->lockname = strconcat (file_to_lock, EXTSEP_S "lock", NULL); + if (!h->lockname) + { + all_lockfiles = h->next; + UNLOCK_all_lockfiles (); + xfree (h); + return NULL; + } + + /* If would be nice if we would use the FILE_FLAG_DELETE_ON_CLOSE + along with FILE_SHARE_DELETE but that does not work due to a race + condition: Despite the OPEN_ALWAYS flag CreateFile may return an + error and we can't reliable create/open the lock file unless we + would wait here until it works - however there are other valid + reasons why a lock file can't be created and thus the process + would not stop as expected but spin until Windows crashes. Our + solution is to keep the lock file open; that does not harm. */ + if (any8bitchar (h->lockname)) + { + wchar_t *wname = utf8_to_wchar (h->lockname); + + if (wname) + h->lockhd = CreateFileW (wname, + GENERIC_READ|GENERIC_WRITE, + FILE_SHARE_READ|FILE_SHARE_WRITE, + NULL, OPEN_ALWAYS, 0, NULL); + else + h->lockhd = INVALID_HANDLE_VALUE; + xfree (wname); + } + else + h->lockhd = CreateFileA (h->lockname, + GENERIC_READ|GENERIC_WRITE, + FILE_SHARE_READ|FILE_SHARE_WRITE, + NULL, OPEN_ALWAYS, 0, NULL); + if (h->lockhd == INVALID_HANDLE_VALUE) + { + int saveerrno = map_w32_to_errno (GetLastError ()); + all_lockfiles = h->next; + UNLOCK_all_lockfiles (); + my_error_2 (_("can't create '%s': %s\n"), h->lockname, w32_strerror (-1)); + xfree (h->lockname); + xfree (h); + my_set_errno (saveerrno); + return NULL; + } + return h; +} +#endif /*HAVE_DOSISH_SYSTEM*/ + + +/* Create a lockfile for a file name FILE_TO_LOCK and returns an + object of type dotlock_t which may be used later to actually acquire + the lock. A cleanup routine gets installed to cleanup left over + locks or other files used internally by the lock mechanism. + + Calling this function with NULL does only install the atexit + handler and may thus be used to assure that the cleanup is called + after all other atexit handlers. + + This function creates a lock file in the same directory as + FILE_TO_LOCK using that name and a suffix of ".lock". Note that on + POSIX systems a temporary file ".#lk.<hostname>.pid[.threadid] is + used. + + FLAGS must be 0. + + The function returns an new handle which needs to be released using + destroy_dotlock but gets also released at the termination of the + process. On error NULL is returned. + */ + +dotlock_t +dotlock_create (const char *file_to_lock, unsigned int flags) +{ + static int initialized; + dotlock_t h; + + if ( !initialized ) + { + atexit (dotlock_remove_lockfiles); + initialized = 1; + } + + if ( !file_to_lock ) + return NULL; /* Only initialization was requested. */ + + if (flags) + { + my_set_errno (EINVAL); + return NULL; + } + + h = xtrycalloc (1, sizeof *h); + if (!h) + return NULL; + h->extra_fd = -1; + + if (never_lock) + { + h->disable = 1; + LOCK_all_lockfiles (); + h->next = all_lockfiles; + all_lockfiles = h; + UNLOCK_all_lockfiles (); + return h; + } + +#ifdef HAVE_DOSISH_SYSTEM + return dotlock_create_w32 (h, file_to_lock); +#else /*!HAVE_DOSISH_SYSTEM */ + return dotlock_create_unix (h, file_to_lock); +#endif /*!HAVE_DOSISH_SYSTEM*/ +} + + + +/* Convenience function to store a file descriptor (or any other + integer value) in the context of handle H. */ +void +dotlock_set_fd (dotlock_t h, int fd) +{ + h->extra_fd = fd; +} + +/* Convenience function to retrieve a file descriptor (or any other + integer value) stored in the context of handle H. */ +int +dotlock_get_fd (dotlock_t h) +{ + return h->extra_fd; +} + + + +#ifdef HAVE_POSIX_SYSTEM +/* Unix specific code of destroy_dotlock. */ +static void +dotlock_destroy_unix (dotlock_t h) +{ + if (h->locked && h->lockname) + unlink (h->lockname); + if (h->tname && !h->use_o_excl) + unlink (h->tname); + xfree (h->tname); +} +#endif /*HAVE_POSIX_SYSTEM*/ + + +#ifdef HAVE_DOSISH_SYSTEM +/* Windows specific code of destroy_dotlock. */ +static void +dotlock_destroy_w32 (dotlock_t h) +{ + if (h->locked) + { + OVERLAPPED ovl; + + memset (&ovl, 0, sizeof ovl); + UnlockFileEx (h->lockhd, 0, 1, 0, &ovl); + } + CloseHandle (h->lockhd); +} +#endif /*HAVE_DOSISH_SYSTEM*/ + + +/* Destroy the lock handle H and release the lock. */ +void +dotlock_destroy (dotlock_t h) +{ + dotlock_t hprev, htmp; + + if ( !h ) + return; + + /* First remove the handle from our global list of all locks. */ + LOCK_all_lockfiles (); + for (hprev=NULL, htmp=all_lockfiles; htmp; hprev=htmp, htmp=htmp->next) + if (htmp == h) + { + if (hprev) + hprev->next = htmp->next; + else + all_lockfiles = htmp->next; + h->next = NULL; + break; + } + UNLOCK_all_lockfiles (); + + /* Then destroy the lock. */ + if (!h->disable) + { +#ifdef HAVE_DOSISH_SYSTEM + dotlock_destroy_w32 (h); +#else /* !HAVE_DOSISH_SYSTEM */ + dotlock_destroy_unix (h); +#endif /* HAVE_DOSISH_SYSTEM */ + xfree (h->lockname); + } + xfree(h); +} + + +/* Return true if H has been taken. */ +int +dotlock_is_locked (dotlock_t h) +{ + return h && !!h->locked; +} + + + +#ifdef HAVE_POSIX_SYSTEM +/* Unix specific code of make_dotlock. Returns 0 on success and -1 on + error. */ +static int +dotlock_take_unix (dotlock_t h, long timeout) +{ + int wtime = 0; + int sumtime = 0; + int pid; + int lastpid = -1; + int ownerchanged; + const char *maybe_dead=""; + int same_node; + int saveerrno; + int fd; + + again: + if (h->use_o_excl) + { + /* No hardlink support - use open(O_EXCL). */ + do + { + my_set_errno (0); + fd = open (h->lockname, O_WRONLY|O_CREAT|O_EXCL, + S_IRUSR|S_IRGRP|S_IROTH|S_IWUSR ); + } + while (fd == -1 && errno == EINTR); + + if (fd == -1 && errno == EEXIST) + ; /* Lock held by another process. */ + else if (fd == -1) + { + saveerrno = errno; + my_error_2 ("lock not made: open(O_EXCL) of '%s' failed: %s\n", + h->lockname, strerror (saveerrno)); + my_set_errno (saveerrno); + return -1; + } + else + { + char pidstr[16]; + + snprintf (pidstr, sizeof pidstr, "%10d\n", (int)getpid()); + if (write (fd, pidstr, 11 ) == 11 + && write (fd, h->tname + h->nodename_off,h->nodename_len) + == h->nodename_len + && write (fd, "\n", 1) == 1 + && !close (fd)) + { + h->locked = 1; + return 0; + } + /* Write error. */ + saveerrno = errno; + my_error_2 ("lock not made: writing to '%s' failed: %s\n", + h->lockname, strerror (errno)); + close (fd); + unlink (h->lockname); + my_set_errno (saveerrno); + return -1; + } + } + else /* Standard method: Use hardlinks. */ + { + struct stat sb; + + /* We ignore the return value of link() because it is unreliable. */ + (void) link (h->tname, h->lockname); + + if (stat (h->tname, &sb)) + { + saveerrno = errno; + my_error_1 ("lock not made: Oops: stat of tmp file failed: %s\n", + strerror (errno)); + /* In theory this might be a severe error: It is possible + that link succeeded but stat failed due to changed + permissions. We can't do anything about it, though. */ + my_set_errno (saveerrno); + return -1; + } + + if (sb.st_nlink == 2) + { + h->locked = 1; + return 0; /* Okay. */ + } + } + + /* Check for stale lock files. */ + if ( (pid = read_lockfile (h, &same_node, &fd)) == -1 ) + { + if ( errno != ENOENT ) + { + saveerrno = errno; + my_info_0 ("cannot read lockfile\n"); + my_set_errno (saveerrno); + return -1; + } + my_info_0 ("lockfile disappeared\n"); + goto again; + } + else if ( (pid == getpid() && same_node) + || (same_node && kill (pid, 0) && errno == ESRCH) ) + /* Stale lockfile is detected. */ + { + struct stat sb; + + /* Check if it's unlocked during examining the lockfile. */ + if (fstat (fd, &sb) || sb.st_nlink == 0) + { + /* It's gone already by another process. */ + close (fd); + goto again; + } + + /* + * Here, although it's quite _rare_, we have a race condition. + * + * When multiple processes race on a stale lockfile, detecting + * AND removing should be done atomically. That is, to work + * correctly, the file to be removed should be the one which is + * examined for detection. + * + * But, when it's not atomic, consider the case for us where it + * takes some time between the detection and the removal of the + * lockfile. + * + * In this situation, it is possible that the file which was + * detected as stale is already removed by another process and + * then new lockfile is created (by that process or other one). + * + * And it is newly created valid lockfile which is going to be + * removed by us. + * + * Consider this long comment as it expresses possible (long) + * time between fstat above and unlink below; Meanwhile, the + * lockfile in question may be removed and there may be new + * valid one. + * + * In short, when you see the message of removing stale lockfile + * when there are multiple processes for the work, there is + * (very) little possibility something went wrong. + */ + + unlink (h->lockname); + my_info_1 (_("removing stale lockfile (created by %d)\n"), pid); + close (fd); + goto again; + } + + close (fd); + if (lastpid == -1) + lastpid = pid; + ownerchanged = (pid != lastpid); + + if (timeout) + { + struct timeval tv; + + /* Wait until lock has been released. We use increasing retry + intervals of 50ms, 100ms, 200ms, 400ms, 800ms, 2s, 4s and 8s + but reset it if the lock owner meanwhile changed. */ + if (!wtime || ownerchanged) + wtime = 50; + else if (wtime < 800) + wtime *= 2; + else if (wtime == 800) + wtime = 2000; + else if (wtime < 8000) + wtime *= 2; + + if (timeout > 0) + { + if (wtime > timeout) + wtime = timeout; + timeout -= wtime; + } + + sumtime += wtime; + if (sumtime >= 1500) + { + sumtime = 0; + my_info_3 (_("waiting for lock (held by %d%s) %s...\n"), + pid, maybe_dead, maybe_deadlock(h)? _("(deadlock?) "):""); + } + + + tv.tv_sec = wtime / 1000; + tv.tv_usec = (wtime % 1000) * 1000; + select (0, NULL, NULL, NULL, &tv); + goto again; + } + + my_set_errno (EACCES); + return -1; +} +#endif /*HAVE_POSIX_SYSTEM*/ + + +#ifdef HAVE_DOSISH_SYSTEM +/* Windows specific code of make_dotlock. Returns 0 on success and -1 on + error. */ +static int +dotlock_take_w32 (dotlock_t h, long timeout) +{ + int wtime = 0; + int w32err; + OVERLAPPED ovl; + + again: + /* Lock one byte at offset 0. The offset is given by OVL. */ + memset (&ovl, 0, sizeof ovl); + if (LockFileEx (h->lockhd, (LOCKFILE_EXCLUSIVE_LOCK + | LOCKFILE_FAIL_IMMEDIATELY), 0, 1, 0, &ovl)) + { + h->locked = 1; + return 0; /* okay */ + } + + w32err = GetLastError (); + if (w32err != ERROR_LOCK_VIOLATION) + { + my_error_2 (_("lock '%s' not made: %s\n"), + h->lockname, w32_strerror (w32err)); + my_set_errno (map_w32_to_errno (w32err)); + return -1; + } + + if (timeout) + { + /* Wait until lock has been released. We use retry intervals of + 50ms, 100ms, 200ms, 400ms, 800ms, 2s, 4s and 8s. */ + if (!wtime) + wtime = 50; + else if (wtime < 800) + wtime *= 2; + else if (wtime == 800) + wtime = 2000; + else if (wtime < 8000) + wtime *= 2; + + if (timeout > 0) + { + if (wtime > timeout) + wtime = timeout; + timeout -= wtime; + } + + if (wtime >= 800) + my_info_1 (_("waiting for lock %s...\n"), h->lockname); + + Sleep (wtime); + goto again; + } + + my_set_errno (EACCES); + return -1; +} +#endif /*HAVE_DOSISH_SYSTEM*/ + + +/* Take a lock on H. A value of 0 for TIMEOUT returns immediately if + the lock can't be taken, -1 waits forever (hopefully not), other + values wait for TIMEOUT milliseconds. Returns: 0 on success */ +int +dotlock_take (dotlock_t h, long timeout) +{ + int ret; + + if ( h->disable ) + { + h->locked = 1; + return 0; /* Locks are completely disabled. Return success. */ + } + + if ( h->locked ) + { + /* my_debug_1 ("'%s' is already locked (%s)\n", h->lockname); */ + return 0; + } + +#ifdef HAVE_DOSISH_SYSTEM + ret = dotlock_take_w32 (h, timeout); +#else /*!HAVE_DOSISH_SYSTEM*/ + ret = dotlock_take_unix (h, timeout); +#endif /*!HAVE_DOSISH_SYSTEM*/ + + return ret; +} + + + +#ifdef HAVE_POSIX_SYSTEM +/* Unix specific code of release_dotlock. */ +static int +dotlock_release_unix (dotlock_t h) +{ + int pid, same_node; + int saveerrno; + + pid = read_lockfile (h, &same_node, NULL); + if ( pid == -1 ) + { + saveerrno = errno; + my_error_0 ("release_dotlock: lockfile error\n"); + my_set_errno (saveerrno); + return -1; + } + if ( pid != getpid() || !same_node ) + { + my_error_1 ("release_dotlock: not our lock (pid=%d)\n", pid); + my_set_errno (EACCES); + return -1; + } + + if ( unlink( h->lockname ) ) + { + saveerrno = errno; + my_error_1 ("release_dotlock: error removing lockfile '%s'\n", + h->lockname); + my_set_errno (saveerrno); + return -1; + } + /* Fixme: As an extra check we could check whether the link count is + now really at 1. */ + return 0; +} +#endif /*HAVE_POSIX_SYSTEM */ + + +#ifdef HAVE_DOSISH_SYSTEM +/* Windows specific code of release_dotlock. */ +static int +dotlock_release_w32 (dotlock_t h) +{ + OVERLAPPED ovl; + + memset (&ovl, 0, sizeof ovl); + if (!UnlockFileEx (h->lockhd, 0, 1, 0, &ovl)) + { + int saveerrno = map_w32_to_errno (GetLastError ()); + my_error_2 ("release_dotlock: error removing lockfile '%s': %s\n", + h->lockname, w32_strerror (-1)); + my_set_errno (saveerrno); + return -1; + } + + return 0; +} +#endif /*HAVE_DOSISH_SYSTEM */ + + +/* Release a lock. Returns 0 on success. */ +int +dotlock_release (dotlock_t h) +{ + int ret; + + /* To avoid atexit race conditions we first check whether there are + any locks left. It might happen that another atexit handler + tries to release the lock while the atexit handler of this module + already ran and thus H is undefined. */ + LOCK_all_lockfiles (); + ret = !all_lockfiles; + UNLOCK_all_lockfiles (); + if (ret) + return 0; + + if ( h->disable ) + { + h->locked = 0; + return 0; + } + + if ( !h->locked ) + { + /* my_debug_1 ("Oops, '%s' is not locked (%s)\n", h->lockname); */ + return 0; + } + +#ifdef HAVE_DOSISH_SYSTEM + ret = dotlock_release_w32 (h); +#else + ret = dotlock_release_unix (h); +#endif + + if (!ret) + h->locked = 0; + return ret; +} + + + +/* Remove all lockfiles. This is called by the atexit handler + installed by this module but may also be called by other + termination handlers. */ +void +dotlock_remove_lockfiles (void) +{ + dotlock_t h, h2; + + /* First set the lockfiles list to NULL so that for example + dotlock_release is aware that this function is currently + running. */ + LOCK_all_lockfiles (); + h = all_lockfiles; + all_lockfiles = NULL; + UNLOCK_all_lockfiles (); + + while ( h ) + { + h2 = h->next; + dotlock_destroy (h); + h = h2; + } +} |