journal: don't force FS_NOCOW_FL on new journal files, but warn if it is missing

This way users have the freedom to set or unset the FS_NOCOW_FL flag on
their journal files by setting it on the journal directory. Since our
default tmpfiles configuration now sets this flag on the directory the
flag is set by default on new files, however people can opt-out of this
by masking the tmpfiles file for it.

1 files changed, 36 insertions, 10 deletions

diff --git a/src/journal/journal-file.c b/src/journal/journal-file.c
index a432eb08a6..be6a5522fa 100644
--- a/src/journal/journal-file.c
+++ b/src/journal/journal-file.c
@@ -2522,6 +2522,41 @@ void journal_file_print_header(JournalFile *f) {
                 printf("Disk usage: %s\n", format_bytes(bytes, sizeof(bytes), (off_t) st.st_blocks * 512ULL));
 }
 
+static int journal_file_warn_btrfs(JournalFile *f) {
+        unsigned attrs;
+        int r;
+
+        assert(f);
+
+        /* Before we write anything, check if the COW logic is turned
+         * off on btrfs. Given our write pattern that is quite
+         * unfriendly to COW file systems this should greatly improve
+         * performance on COW file systems, such as btrfs, at the
+         * expense of data integrity features (which shouldn't be too
+         * bad, given that we do our own checksumming). */
+
+        r = btrfs_is_filesystem(f->fd);
+        if (r < 0)
+                return log_warning_errno(r, "Failed to determine if journal is on btrfs: %m");
+        if (!r)
+                return 0;
+
+        r = read_attr_fd(f->fd, &attrs);
+        if (r < 0)
+                return log_warning_errno(r, "Failed to read file attributes: %m");
+
+        if (attrs & FS_NOCOW_FL) {
+                log_debug("Detected btrfs file system with copy-on-write disabled, all is good.");
+                return 0;
+        }
+
+        log_notice("Creating journal file %s on a btrfs file system, and copy-on-write is enabled. "
+                   "This is likely to slow down journal access substantially, please consider turning "
+                   "off the copy-on-write file attribute on the journal directory, using chattr +C.", f->path);
+
+        return 1;
+}
+
 int journal_file_open(
                 const char *fname,
                 int flags,
@@ -2602,16 +2637,7 @@ int journal_file_open(
 
         if (f->last_stat.st_size == 0 && f->writable) {
 
-                /* Before we write anything, turn off COW logic. Given
-                 * our write pattern that is quite unfriendly to COW
-                 * file systems this should greatly improve
-                 * performance on COW file systems, such as btrfs, at
-                 * the expense of data integrity features (which
-                 * shouldn't be too bad, given that we do our own
-                 * checksumming). */
-                r = chattr_fd(f->fd, FS_NOCOW_FL, FS_NOCOW_FL);
-                if (r < 0 && r != -ENOTTY)
-                        log_warning_errno(r, "Failed to set file attributes: %m");
+                (void) journal_file_warn_btrfs(f);
 
                 /* Let's attach the creation time to the journal file,
                  * so that the vacuuming code knows the age of this