io/file_change_detection.c

   1 /* Detecting file changes using modification times.
   2    Copyright (C) 2017-2021 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_t64 *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 = (struct __timespec64) { st->st_mtim.tv_sec,
  60                                             st->st_mtim.tv_nsec };
  61       file->ctime = (struct __timespec64) { st->st_ctim.tv_sec,
  62                                             st->st_ctim.tv_nsec };
  63     }
  64 }
  65 libc_hidden_def (__file_change_detection_for_stat)
  66
  67 bool
  68 __file_change_detection_for_path (struct file_change_detection *file,
  69                                   const char *path)
  70 {
  71   struct __stat64_t64 st;
  72   if (__stat64_time64 (path, &st) != 0)
  73     switch (errno)
  74       {
  75       case EACCES:
  76       case EISDIR:
  77       case ELOOP:
  78       case ENOENT:
  79       case ENOTDIR:
  80       case EPERM:
  81         /* Ignore errors due to file system contents.  Instead, treat
  82            the file as empty.  */
  83         file->size = 0;
  84         return true;
  85       default:
  86         /* Other errors are fatal.  */
  87         return false;
  88       }
  89   else /* stat64 was successfull.  */
  90     {
  91       __file_change_detection_for_stat (file, &st);
  92       return true;
  93     }
  94 }
  95 libc_hidden_def (__file_change_detection_for_path)
  96
  97 bool
  98 __file_change_detection_for_fp (struct file_change_detection *file,
  99                                 FILE *fp)
 100 {
 101   if (fp == NULL)
 102     {
 103       /* The file does not exist.  */
 104       file->size = 0;
 105       return true;
 106     }
 107   else
 108     {
 109       struct __stat64_t64 st;
 110       if (__fstat64_time64 (__fileno (fp), &st) != 0)
 111         /* If we already have a file descriptor, all errors are fatal.  */
 112         return false;
 113       else
 114         {
 115           __file_change_detection_for_stat (file, &st);
 116           return true;
 117         }
 118     }
 119 }
 120 libc_hidden_def (__file_change_detection_for_fp)