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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>
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