io/file_change_detection.c

   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 <file_change_detection.h>
  20
  21 #include <errno.h>
  22 #include <stddef.h>
  23
  24 bool
  25 __file_is_unchanged (const struct file_change_detection *left,
  26                      const struct file_change_detection *right)
  27 {
  28   if (left->size < 0 || right->size < 0)
  29     /* Negative sizes are used as markers and never match.  */
  30     return false;
  31   else if (left->size == 0 && right->size == 0)
  32     /* Both files are empty or do not exist, so they have the same
  33        content, no matter what the other fields indicate.  */
  34     return true;
  35   else
  36     return left->size == right->size
  37       && left->ino == right->ino
  38       && left->mtime.tv_sec == right->mtime.tv_sec
  39       && left->mtime.tv_nsec == right->mtime.tv_nsec
  40       && left->ctime.tv_sec == right->ctime.tv_sec
  41       && left->ctime.tv_nsec == right->ctime.tv_nsec;
  42 }
  43 libc_hidden_def (__file_is_unchanged)
  44
  45 void
  46 __file_change_detection_for_stat (struct file_change_detection *file,
  47                                   const struct stat64 *st)
  48 {
  49   if (S_ISDIR (st->st_mode))
  50     /* Treat as empty file.  */
  51     file->size = 0;
  52   else if (!S_ISREG (st->st_mode))
  53     /* Non-regular files cannot be cached.  */
  54     file->size = -1;
  55   else
  56     {
  57       file->size = st->st_size;
  58       file->ino = st->st_ino;
  59       file->mtime = st->st_mtim;
  60       file->ctime = st->st_ctim;
  61     }
  62 }
  63 libc_hidden_def (__file_change_detection_for_stat)
  64
  65 bool
  66 __file_change_detection_for_path (struct file_change_detection *file,
  67                                   const char *path)
  68 {
  69   struct stat64 st;
  70   if (__stat64 (path, &st) != 0)
  71     switch (errno)
  72       {
  73       case EACCES:
  74       case EISDIR:
  75       case ELOOP:
  76       case ENOENT:
  77       case ENOTDIR:
  78       case EPERM:
  79         /* Ignore errors due to file system contents.  Instead, treat
  80            the file as empty.  */
  81         file->size = 0;
  82         return true;
  83       default:
  84         /* Other errors are fatal.  */
  85         return false;
  86       }
  87   else /* stat64 was successfull.  */
  88     {
  89       __file_change_detection_for_stat (file, &st);
  90       return true;
  91     }
  92 }
  93 libc_hidden_def (__file_change_detection_for_path)
  94
  95 bool
  96 __file_change_detection_for_fp (struct file_change_detection *file,
  97                                 FILE *fp)
  98 {
  99   if (fp == NULL)
 100     {
 101       /* The file does not exist.  */
 102       file->size = 0;
 103       return true;
 104     }
 105   else
 106     {
 107       struct stat64 st;
 108       if (__fstat64 (__fileno (fp), &st) != 0)
 109         /* If we already have a file descriptor, all errors are fatal.  */
 110         return false;
 111       else
 112         {
 113           __file_change_detection_for_stat (file, &st);
 114           return true;
 115         }
 116     }
 117 }
 118 libc_hidden_def (__file_change_detection_for_fp)