diff options
Diffstat (limited to 'include')
| -rw-r--r-- | include/file_change_detection.h | 140 |
1 files changed, 140 insertions, 0 deletions
diff --git a/include/file_change_detection.h b/include/file_change_detection.h new file mode 100644 index 0000000000..aaed0a9b6d --- /dev/null +++ b/include/file_change_detection.h @@ -0,0 +1,140 @@ +/* Detecting file changes using modification times. + Copyright (C) 2017-2020 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library 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 2.1 of the License, or (at your option) any later version. + + The GNU C Library 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 the GNU C Library; if not, see + <https://www.gnu.org/licenses/>. */ + +#include <errno.h> +#include <stdbool.h> +#include <stddef.h> +#include <stdio.h> +#include <sys/stat.h> +#include <sys/types.h> + +/* Items for identifying a particular file version. Excerpt from + struct stat64. */ +struct file_change_detection +{ + /* Special values: 0 if file does not exist. -1 to force mismatch + with the next comparison. */ + off64_t size; + + ino64_t ino; + struct timespec mtime; + struct timespec ctime; +}; + +/* Returns true if *LEFT and *RIGHT describe the same version of the + same file. */ +static bool __attribute__ ((unused)) +file_is_unchanged (const struct file_change_detection *left, + const struct file_change_detection *right) +{ + if (left->size < 0 || right->size < 0) + /* Negative sizes are used as markers and never match. */ + return false; + else if (left->size == 0 && right->size == 0) + /* Both files are empty or do not exist, so they have the same + content, no matter what the other fields indicate. */ + return true; + else + return left->size == right->size + && left->ino == right->ino + && left->mtime.tv_sec == right->mtime.tv_sec + && left->mtime.tv_nsec == right->mtime.tv_nsec + && left->ctime.tv_sec == right->ctime.tv_sec + && left->ctime.tv_nsec == right->ctime.tv_nsec; +} + +/* Extract file change information to *FILE from the stat buffer + *ST. */ +static void __attribute__ ((unused)) +file_change_detection_for_stat (struct file_change_detection *file, + const struct stat64 *st) +{ + if (S_ISDIR (st->st_mode)) + /* Treat as empty file. */ + file->size = 0; + else if (!S_ISREG (st->st_mode)) + /* Non-regular files cannot be cached. */ + file->size = -1; + else + { + file->size = st->st_size; + file->ino = st->st_ino; + file->mtime = st->st_mtim; + file->ctime = st->st_ctim; + } +} + +/* Writes file change information for PATH to *FILE. Returns true on + success. For benign errors, *FILE is cleared, and true is + returned. For errors indicating resource outages and the like, + false is returned. */ +static bool __attribute__ ((unused)) +file_change_detection_for_path (struct file_change_detection *file, + const char *path) +{ + struct stat64 st; + if (stat64 (path, &st) != 0) + switch (errno) + { + case EACCES: + case EISDIR: + case ELOOP: + case ENOENT: + case ENOTDIR: + case EPERM: + /* Ignore errors due to file system contents. Instead, treat + the file as empty. */ + file->size = 0; + return true; + default: + /* Other errors are fatal. */ + return false; + } + else /* stat64 was successfull. */ + { + file_change_detection_for_stat (file, &st); + return true; + } +} + +/* Writes file change information for the stream FP to *FILE. Returns + ture on success, false on failure. If FP is NULL, treat the file + as non-existing. */ +static bool __attribute__ ((unused)) +file_change_detection_for_fp (struct file_change_detection *file, + FILE *fp) +{ + if (fp == NULL) + { + /* The file does not exist. */ + file->size = 0; + return true; + } + else + { + struct stat64 st; + if (fstat64 (__fileno (fp), &st) != 0) + /* If we already have a file descriptor, all errors are fatal. */ + return false; + else + { + file_change_detection_for_stat (file, &st); + return true; + } + } +} |