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From 245ad27530ae9e99242ebfa1631bd7fc8f66a59c Mon Sep 17 00:00:00 2001
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From: Lennart Poettering <lennart@poettering.net>
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Date: Wed, 22 Apr 2015 13:20:49 +0200
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Subject: [PATCH] journal: don't force FS_NOCOW_FL on new journal files, but
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 warn if it is missing
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This way users have the freedom to set or unset the FS_NOCOW_FL flag on
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their journal files by setting it on the journal directory. Since our
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default tmpfiles configuration now sets this flag on the directory the
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flag is set by default on new files, however people can opt-out of this
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by masking the tmpfiles file for it.
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(cherry picked from commit fc68c92973e5437ee0489c1bc80d80f0a7b6ca0b)
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Conflicts:
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	src/journal/journal-file.c
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Resolves: #1299714
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---
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 src/journal/journal-file.c | 46 ++++++++++++++++++++++++++++++++++++----------
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 1 file changed, 36 insertions(+), 10 deletions(-)
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diff --git a/src/journal/journal-file.c b/src/journal/journal-file.c
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index 8034b771d..0fd59ec07 100644
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--- a/src/journal/journal-file.c
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+++ b/src/journal/journal-file.c
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@@ -2543,6 +2543,41 @@ void journal_file_print_header(JournalFile *f) {
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                 printf("Disk usage: %s\n", format_bytes(bytes, sizeof(bytes), (off_t) st.st_blocks * 512ULL));
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 }
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+static int journal_file_warn_btrfs(JournalFile *f) {
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+        unsigned attrs;
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+        int r;
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+
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+        assert(f);
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+
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+        /* Before we write anything, check if the COW logic is turned
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+         * off on btrfs. Given our write pattern that is quite
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+         * unfriendly to COW file systems this should greatly improve
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+         * performance on COW file systems, such as btrfs, at the
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+         * expense of data integrity features (which shouldn't be too
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+         * bad, given that we do our own checksumming). */
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+
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+        r = btrfs_is_filesystem(f->fd);
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+        if (r < 0)
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+                return log_warning_errno(r, "Failed to determine if journal is on btrfs: %m");
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+        if (!r)
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+                return 0;
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+
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+        r = read_attr_fd(f->fd, &attrs);
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+        if (r < 0)
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+                return log_warning_errno(r, "Failed to read file attributes: %m");
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+
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+        if (attrs & FS_NOCOW_FL) {
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+                log_debug("Detected btrfs file system with copy-on-write disabled, all is good.");
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+                return 0;
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+        }
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+
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+        log_notice("Creating journal file %s on a btrfs file system, and copy-on-write is enabled. "
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+                   "This is likely to slow down journal access substantially, please consider turning "
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+                   "off the copy-on-write file attribute on the journal directory, using chattr +C.", f->path);
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+
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+        return 1;
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+}
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+
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 int journal_file_open(
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                 const char *fname,
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                 int flags,
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@@ -2623,16 +2658,7 @@ int journal_file_open(
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         if (f->last_stat.st_size == 0 && f->writable) {
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-                /* Before we write anything, turn off COW logic. Given
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-                 * our write pattern that is quite unfriendly to COW
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-                 * file systems this should greatly improve
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-                 * performance on COW file systems, such as btrfs, at
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-                 * the expense of data integrity features (which
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-                 * shouldn't be too bad, given that we do our own
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-                 * checksumming). */
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-                r = chattr_fd(f->fd, true, FS_NOCOW_FL);
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-                if (r < 0 && r != -ENOTTY)
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-                        log_warning_errno(r, "Failed to set file attributes: %m");
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+                (void) journal_file_warn_btrfs(f);
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                 /* Let's attach the creation time to the journal file,
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                  * so that the vacuuming code knows the age of this