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Diffstat (limited to '')
| -rw-r--r-- | lib/fchdir.c | 204 |
1 files changed, 204 insertions, 0 deletions
diff --git a/lib/fchdir.c b/lib/fchdir.c new file mode 100644 index 0000000..880b137 --- /dev/null +++ b/lib/fchdir.c @@ -0,0 +1,204 @@ +/* fchdir replacement. + Copyright (C) 2006-2023 Free Software Foundation, Inc. + + This file is free software: you can redistribute it and/or modify + it under the terms of 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. + + This file 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 Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public License + along with this program. If not, see <https://www.gnu.org/licenses/>. */ + +#include <config.h> + +/* Specification. */ +#include <unistd.h> + +#include <dirent.h> +#include <errno.h> +#include <fcntl.h> +#include <stdlib.h> +#include <string.h> +#include <sys/types.h> +#include <sys/stat.h> + +#include "assure.h" +#include "filename.h" +#include "filenamecat.h" + +#ifndef REPLACE_OPEN_DIRECTORY +# define REPLACE_OPEN_DIRECTORY 0 +#endif + +/* This replacement assumes that a directory is not renamed while opened + through a file descriptor. + + FIXME: On mingw, this would be possible to enforce if we were to + also open a HANDLE to each directory currently visited by a file + descriptor, since mingw refuses to rename any in-use file system + object. */ + +/* Array of file descriptors opened. If REPLACE_OPEN_DIRECTORY or if it points + to a directory, it stores info about this directory. */ +typedef struct +{ + char *name; /* Absolute name of the directory, or NULL. */ +} dir_info_t; +static dir_info_t *dirs; +static size_t dirs_allocated; + +/* Try to ensure dirs has enough room for a slot at index fd; free any + contents already in that slot. Return false and set errno to + ENOMEM on allocation failure. */ +static bool +ensure_dirs_slot (size_t fd) +{ + if (fd < dirs_allocated) + free (dirs[fd].name); + else + { + size_t new_allocated; + dir_info_t *new_dirs; + + new_allocated = 2 * dirs_allocated + 1; + if (new_allocated <= fd) + new_allocated = fd + 1; + new_dirs = + (dirs != NULL + ? (dir_info_t *) realloc (dirs, new_allocated * sizeof *dirs) + : (dir_info_t *) malloc (new_allocated * sizeof *dirs)); + if (new_dirs == NULL) + return false; + memset (new_dirs + dirs_allocated, 0, + (new_allocated - dirs_allocated) * sizeof *dirs); + dirs = new_dirs; + dirs_allocated = new_allocated; + } + return true; +} + +/* Return an absolute name of DIR in malloc'd storage. + Upon failure, return NULL with errno set. */ +static char * +get_name (char const *dir) +{ + char *cwd; + char *result; + + if (IS_ABSOLUTE_FILE_NAME (dir)) + return strdup (dir); + + /* We often encounter "."; treat it as a special case. */ + cwd = getcwd (NULL, 0); + if (!cwd || (dir[0] == '.' && dir[1] == '\0')) + return cwd; + + result = mfile_name_concat (cwd, dir, NULL); + free (cwd); + return result; +} + +/* Hook into the gnulib replacements for open() and close() to keep track + of the open file descriptors. */ + +/* Close FD, cleaning up any fd to name mapping if fd was visiting a + directory. */ +void +_gl_unregister_fd (int fd) +{ + if (fd >= 0 && fd < dirs_allocated) + { + free (dirs[fd].name); + dirs[fd].name = NULL; + } +} + +/* Mark FD as visiting FILENAME. FD must be non-negative, and refer + to an open file descriptor. If REPLACE_OPEN_DIRECTORY is non-zero, + this should only be called if FD is visiting a directory. Close FD + and return -1 with errno set if there is insufficient memory to track + the directory name; otherwise return FD. */ +int +_gl_register_fd (int fd, const char *filename) +{ + struct stat statbuf; + + assure (0 <= fd); + if (REPLACE_OPEN_DIRECTORY + || (fstat (fd, &statbuf) == 0 && S_ISDIR (statbuf.st_mode))) + { + if (!ensure_dirs_slot (fd) + || (dirs[fd].name = get_name (filename)) == NULL) + { + int saved_errno = errno; + close (fd); + errno = saved_errno; + return -1; + } + } + return fd; +} + +/* Mark NEWFD as a duplicate of OLDFD; useful from dup, dup2, dup3, + and fcntl. Both arguments must be valid and distinct file + descriptors. Close NEWFD and return -1 if OLDFD is tracking a + directory, but there is insufficient memory to track the same + directory in NEWFD; otherwise return NEWFD. */ +int +_gl_register_dup (int oldfd, int newfd) +{ + assure (0 <= oldfd && 0 <= newfd && oldfd != newfd); + if (oldfd < dirs_allocated && dirs[oldfd].name) + { + /* Duplicated a directory; must ensure newfd is allocated. */ + if (!ensure_dirs_slot (newfd) + || (dirs[newfd].name = strdup (dirs[oldfd].name)) == NULL) + { + int saved_errno = errno; + close (newfd); + errno = saved_errno; + newfd = -1; + } + } + else if (newfd < dirs_allocated) + { + /* Duplicated a non-directory; ensure newfd is cleared. */ + free (dirs[newfd].name); + dirs[newfd].name = NULL; + } + return newfd; +} + +/* If FD is currently visiting a directory, then return the name of + that directory. Otherwise, return NULL and set errno. */ +const char * +_gl_directory_name (int fd) +{ + if (0 <= fd && fd < dirs_allocated && dirs[fd].name != NULL) + return dirs[fd].name; + /* At this point, fd is either invalid, or open but not a directory. + If dup2 fails, errno is correctly EBADF. */ + if (0 <= fd) + { + if (dup2 (fd, fd) == fd) + errno = ENOTDIR; + } + else + errno = EBADF; + return NULL; +} + + +/* Implement fchdir() in terms of chdir(). */ + +int +fchdir (int fd) +{ + const char *name = _gl_directory_name (fd); + return name ? chdir (name) : -1; +} |