journald: turn off COW for journal files on btrfs

btrfs' COW logic results in heavily fragment journal files, which is
detrimental for perfomance. Hence, turn off COW for journal files as we
create them.

Turning off COW comes at the cost of data integrity guarantees, but this
should be acceptable, given that we do our own checksumming, and
generally have a pretty conservative write pattern.

Also see discussion on linux-btrfs:

http://www.spinics.net/lists/linux-btrfs/msg41001.html

1 files changed, 33 insertions, 0 deletions

diff --git a/src/shared/util.c b/src/shared/util.c
index 6293e967c..88fd78ec8 100644
--- a/src/shared/util.c
+++ b/src/shared/util.c
@@ -62,6 +62,7 @@
 #include <sys/xattr.h>
 #include <libgen.h>
 #include <sys/statvfs.h>
+#include <linux/fs.h>
 #undef basename
 
 #ifdef HAVE_SYS_AUXV_H
@@ -7740,3 +7741,35 @@ int same_fd(int a, int b) {
 
         return fa == fb;
 }
+
+int chattr_fd(int fd, bool b, int mask) {
+        int old_attr, new_attr;
+
+        assert(fd >= 0);
+
+        if (ioctl(fd, FS_IOC_GETFLAGS, &old_attr) < 0)
+                return -errno;
+
+        if (b)
+                new_attr = old_attr | mask;
+        else
+                new_attr = old_attr & ~mask;
+
+        if (new_attr == old_attr)
+                return 0;
+
+        if (ioctl(fd, FS_IOC_SETFLAGS, &new_attr) < 0)
+                return -errno;
+
+        return 0;
+}
+
+int chattr_path(const char *p, bool b, int mask) {
+        _cleanup_close_ int fd = -1;
+
+        fd = open(p, O_RDWR|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW);
+        if (fd < 0)
+                return -errno;
+
+        return chattr_fd(fd, b, mask);
+}