From: Florian Weimer <fweimer@redhat.com>

Date: Tue, 11 Feb 2020 12:52:06 +0000 (+0100)

Subject: Add internal <file_change_detection.h> header file

X-Git-Url: https://sourceware.org/git/?p=glibc.git;a=commitdiff_plain;h=6c80c6e8767b860a5e18e136d04a80be2a8dce15

Add internal <file_change_detection.h> header file

The code started out with bits form resolv/resolv_conf.c, but it

was enhanced to deal with directories and FIFOs in a more predictable

manner.  A test case is included as well.

This will be used to implement the /etc/resolv.conf change detection.

This currently lives in a header file only.  Once there are multiple

users, the implementations should be moved into C files.

---

diff -rupN a/include/file_change_detection.h b/include/file_change_detection.h

--- a/include/file_change_detection.h	1969-12-31 19:00:00.000000000 -0500

+++ b/include/file_change_detection.h	2020-03-25 16:57:24.227929816 -0400

@@ -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;

+        }

+    }

+}

diff -rupN a/io/Makefile b/io/Makefile

--- a/io/Makefile	2020-03-25 16:55:42.442195992 -0400

+++ b/io/Makefile	2020-03-25 16:58:48.571023810 -0400

@@ -74,6 +74,7 @@ tests		:= test-utime test-stat test-stat

 		   tst-posix_fallocate tst-posix_fallocate64 \

 		   tst-fts tst-fts-lfs tst-open-tmpfile \

 		   tst-copy_file_range tst-getcwd-abspath \

+		   tst-file_change_detection

 # Likewise for statx, but we do not need static linking here.

 tests-internal += tst-statx

diff -rupN a/io/tst-file_change_detection.c b/io/tst-file_change_detection.c

--- a/io/tst-file_change_detection.c	1969-12-31 19:00:00.000000000 -0500

+++ b/io/tst-file_change_detection.c	2020-03-25 16:57:24.242930366 -0400

@@ -0,0 +1,206 @@

+/* Test for <file_change_detection.c>.

+   Copyright (C) 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/>.  */

+

+/* The header uses the internal __fileno symbol, which is not

+   available outside of libc (even to internal tests).  */

+#define __fileno(fp) fileno (fp)

+

+#include <file_change_detection.h>

+

+#include <array_length.h>

+#include <stdlib.h>

+#include <support/check.h>

+#include <support/support.h>

+#include <support/temp_file.h>

+#include <support/test-driver.h>

+#include <support/xstdio.h>

+#include <support/xunistd.h>

+#include <unistd.h>

+

+static void

+all_same (struct file_change_detection *array, size_t length)

+{

+  for (size_t i = 0; i < length; ++i)

+    for (size_t j = 0; j < length; ++j)

+      {

+        if (test_verbose > 0)

+          printf ("info: comparing %zu and %zu\n", i, j);

+        TEST_VERIFY (file_is_unchanged (array + i, array + j));

+      }

+}

+

+static void

+all_different (struct file_change_detection *array, size_t length)

+{

+  for (size_t i = 0; i < length; ++i)

+    for (size_t j = 0; j < length; ++j)

+      {

+        if (i == j)

+          continue;

+        if (test_verbose > 0)

+          printf ("info: comparing %zu and %zu\n", i, j);

+        TEST_VERIFY (!file_is_unchanged (array + i, array + j));

+      }

+}

+

+static int

+do_test (void)

+{

+  /* Use a temporary directory with various paths.  */

+  char *tempdir = support_create_temp_directory ("tst-file_change_detection-");

+

+  char *path_dangling = xasprintf ("%s/dangling", tempdir);

+  char *path_does_not_exist = xasprintf ("%s/does-not-exist", tempdir);

+  char *path_empty1 = xasprintf ("%s/empty1", tempdir);

+  char *path_empty2 = xasprintf ("%s/empty2", tempdir);

+  char *path_fifo = xasprintf ("%s/fifo", tempdir);

+  char *path_file1 = xasprintf ("%s/file1", tempdir);

+  char *path_file2 = xasprintf ("%s/file2", tempdir);

+  char *path_loop = xasprintf ("%s/loop", tempdir);

+  char *path_to_empty1 = xasprintf ("%s/to-empty1", tempdir);

+  char *path_to_file1 = xasprintf ("%s/to-file1", tempdir);

+

+  add_temp_file (path_dangling);

+  add_temp_file (path_empty1);

+  add_temp_file (path_empty2);

+  add_temp_file (path_fifo);

+  add_temp_file (path_file1);

+  add_temp_file (path_file2);

+  add_temp_file (path_loop);

+  add_temp_file (path_to_empty1);

+  add_temp_file (path_to_file1);

+

+  xsymlink ("target-does-not-exist", path_dangling);

+  support_write_file_string (path_empty1, "");

+  support_write_file_string (path_empty2, "");

+  TEST_COMPARE (mknod (path_fifo, 0777 | S_IFIFO, 0), 0);

+  support_write_file_string (path_file1, "line\n");

+  support_write_file_string (path_file2, "line\n");

+  xsymlink ("loop", path_loop);

+  xsymlink ("empty1", path_to_empty1);

+  xsymlink ("file1", path_to_file1);

+

+  FILE *fp_file1 = xfopen (path_file1, "r");

+  FILE *fp_file2 = xfopen (path_file2, "r");

+  FILE *fp_empty1 = xfopen (path_empty1, "r");

+  FILE *fp_empty2 = xfopen (path_empty2, "r");

+

+  /* Test for the same (empty) files.  */

+  {

+    struct file_change_detection fcd[10];

+    int i = 0;

+    /* Two empty files always have the same contents.  */

+    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_empty1));

+    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_empty2));

+    /* So does a missing file (which is treated as empty).  */

+    TEST_VERIFY (file_change_detection_for_path (&fcd[i++],

+                                                 path_does_not_exist));

+    /* And a symbolic link loop.  */

+    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_loop));

+    /* And a dangling symbolic link.  */

+    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_dangling));

+    /* And a directory.  */

+    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], tempdir));

+    /* And a symbolic link to an empty file.  */

+    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_to_empty1));

+    /* Likewise for access the file via a FILE *.  */

+    TEST_VERIFY (file_change_detection_for_fp (&fcd[i++], fp_empty1));

+    TEST_VERIFY (file_change_detection_for_fp (&fcd[i++], fp_empty2));

+    /* And a NULL FILE * (missing file).  */

+    TEST_VERIFY (file_change_detection_for_fp (&fcd[i++], NULL));

+    TEST_COMPARE (i, array_length (fcd));

+

+    all_same (fcd, array_length (fcd));

+  }

+

+  /* Symbolic links are resolved.  */

+  {

+    struct file_change_detection fcd[3];

+    int i = 0;

+    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_file1));

+    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_to_file1));

+    TEST_VERIFY (file_change_detection_for_fp (&fcd[i++], fp_file1));

+    TEST_COMPARE (i, array_length (fcd));

+    all_same (fcd, array_length (fcd));

+  }

+

+  /* Test for different files.  */

+  {

+    struct file_change_detection fcd[5];

+    int i = 0;

+    /* The other files are not empty.  */

+    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_empty1));

+    /* These two files have the same contents, but have different file

+       identity.  */

+    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_file1));

+    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_file2));

+    /* FIFOs are always different, even with themselves.  */

+    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_fifo));

+    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_fifo));

+    TEST_COMPARE (i, array_length (fcd));

+    all_different (fcd, array_length (fcd));

+

+    /* Replacing the file with its symbolic link does not make a

+       difference.  */

+    TEST_VERIFY (file_change_detection_for_path (&fcd[1], path_to_file1));

+    all_different (fcd, array_length (fcd));

+  }

+

+  /* Wait for a file change.  Depending on file system time stamp

+     resolution, this subtest blocks for a while.  */

+  for (int use_stdio = 0; use_stdio < 2; ++use_stdio)

+    {

+      struct file_change_detection initial;

+      TEST_VERIFY (file_change_detection_for_path (&initial, path_file1));

+      while (true)

+        {

+          support_write_file_string (path_file1, "line\n");

+          struct file_change_detection current;

+          if (use_stdio)

+            TEST_VERIFY (file_change_detection_for_fp (&current, fp_file1));

+          else

+            TEST_VERIFY (file_change_detection_for_path (&current, path_file1));

+          if (!file_is_unchanged (&initial, &current))

+            break;

+          /* Wait for a bit to reduce system load.  */

+          usleep (100 * 1000);

+        }

+    }

+

+  fclose (fp_empty1);

+  fclose (fp_empty2);

+  fclose (fp_file1);

+  fclose (fp_file2);

+

+  free (path_dangling);

+  free (path_does_not_exist);

+  free (path_empty1);

+  free (path_empty2);

+  free (path_fifo);

+  free (path_file1);

+  free (path_file2);

+  free (path_loop);

+  free (path_to_empty1);

+  free (path_to_file1);

+

+  free (tempdir);

+

+  return 0;

+}

+

+#include <support/test-driver.c>