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6c80c6e8 FW |
1 | /* Detecting file changes using modification times. |
2 | Copyright (C) 2017-2020 Free Software Foundation, Inc. | |
3 | This file is part of the GNU C Library. | |
4 | ||
5 | The GNU C Library is free software; you can redistribute it and/or | |
6 | modify it under the terms of the GNU Lesser General Public | |
7 | License as published by the Free Software Foundation; either | |
8 | version 2.1 of the License, or (at your option) any later version. | |
9 | ||
10 | The GNU C Library is distributed in the hope that it will be useful, | |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
13 | Lesser General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU Lesser General Public | |
16 | License along with the GNU C Library; if not, see | |
17 | <https://www.gnu.org/licenses/>. */ | |
18 | ||
19 | #include <errno.h> | |
20 | #include <stdbool.h> | |
21 | #include <stddef.h> | |
22 | #include <stdio.h> | |
23 | #include <sys/stat.h> | |
24 | #include <sys/types.h> | |
25 | ||
26 | /* Items for identifying a particular file version. Excerpt from | |
27 | struct stat64. */ | |
28 | struct file_change_detection | |
29 | { | |
30 | /* Special values: 0 if file does not exist. -1 to force mismatch | |
31 | with the next comparison. */ | |
32 | off64_t size; | |
33 | ||
34 | ino64_t ino; | |
35 | struct timespec mtime; | |
36 | struct timespec ctime; | |
37 | }; | |
38 | ||
39 | /* Returns true if *LEFT and *RIGHT describe the same version of the | |
40 | same file. */ | |
41 | static bool __attribute__ ((unused)) | |
42 | file_is_unchanged (const struct file_change_detection *left, | |
43 | const struct file_change_detection *right) | |
44 | { | |
45 | if (left->size < 0 || right->size < 0) | |
46 | /* Negative sizes are used as markers and never match. */ | |
47 | return false; | |
48 | else if (left->size == 0 && right->size == 0) | |
49 | /* Both files are empty or do not exist, so they have the same | |
50 | content, no matter what the other fields indicate. */ | |
51 | return true; | |
52 | else | |
53 | return left->size == right->size | |
54 | && left->ino == right->ino | |
55 | && left->mtime.tv_sec == right->mtime.tv_sec | |
56 | && left->mtime.tv_nsec == right->mtime.tv_nsec | |
57 | && left->ctime.tv_sec == right->ctime.tv_sec | |
58 | && left->ctime.tv_nsec == right->ctime.tv_nsec; | |
59 | } | |
60 | ||
61 | /* Extract file change information to *FILE from the stat buffer | |
62 | *ST. */ | |
63 | static void __attribute__ ((unused)) | |
64 | file_change_detection_for_stat (struct file_change_detection *file, | |
65 | const struct stat64 *st) | |
66 | { | |
67 | if (S_ISDIR (st->st_mode)) | |
68 | /* Treat as empty file. */ | |
69 | file->size = 0; | |
70 | else if (!S_ISREG (st->st_mode)) | |
71 | /* Non-regular files cannot be cached. */ | |
72 | file->size = -1; | |
73 | else | |
74 | { | |
75 | file->size = st->st_size; | |
76 | file->ino = st->st_ino; | |
77 | file->mtime = st->st_mtim; | |
78 | file->ctime = st->st_ctim; | |
79 | } | |
80 | } | |
81 | ||
82 | /* Writes file change information for PATH to *FILE. Returns true on | |
83 | success. For benign errors, *FILE is cleared, and true is | |
84 | returned. For errors indicating resource outages and the like, | |
85 | false is returned. */ | |
86 | static bool __attribute__ ((unused)) | |
87 | file_change_detection_for_path (struct file_change_detection *file, | |
88 | const char *path) | |
89 | { | |
90 | struct stat64 st; | |
91 | if (stat64 (path, &st) != 0) | |
92 | switch (errno) | |
93 | { | |
94 | case EACCES: | |
95 | case EISDIR: | |
96 | case ELOOP: | |
97 | case ENOENT: | |
98 | case ENOTDIR: | |
99 | case EPERM: | |
100 | /* Ignore errors due to file system contents. Instead, treat | |
101 | the file as empty. */ | |
102 | file->size = 0; | |
103 | return true; | |
104 | default: | |
105 | /* Other errors are fatal. */ | |
106 | return false; | |
107 | } | |
108 | else /* stat64 was successfull. */ | |
109 | { | |
110 | file_change_detection_for_stat (file, &st); | |
111 | return true; | |
112 | } | |
113 | } | |
114 | ||
115 | /* Writes file change information for the stream FP to *FILE. Returns | |
116 | ture on success, false on failure. If FP is NULL, treat the file | |
117 | as non-existing. */ | |
118 | static bool __attribute__ ((unused)) | |
119 | file_change_detection_for_fp (struct file_change_detection *file, | |
120 | FILE *fp) | |
121 | { | |
122 | if (fp == NULL) | |
123 | { | |
124 | /* The file does not exist. */ | |
125 | file->size = 0; | |
126 | return true; | |
127 | } | |
128 | else | |
129 | { | |
130 | struct stat64 st; | |
131 | if (fstat64 (__fileno (fp), &st) != 0) | |
132 | /* If we already have a file descriptor, all errors are fatal. */ | |
133 | return false; | |
134 | else | |
135 | { | |
136 | file_change_detection_for_stat (file, &st); | |
137 | return true; | |
138 | } | |
139 | } | |
140 | } |