vfs, writeback: replace FS_CGROUP_WRITEBACK with SB_I_CGROUPWB
FS_CGROUP_WRITEBACK indicates whether a file_system_type supports
cgroup writeback; however, different super_blocks of the same
file_system_type may or may not support cgroup writeback depending on
filesystem options. This patch replaces FS_CGROUP_WRITEBACK with a
per-super_block flag.
super_block->s_flags carries some internal flags in the high bits but
it's exposd to userland through uapi header and running out of space
anyway. This patch adds a new field super_block->s_iflags to carry
kernel-internal flags. It is currently only used by the new
SB_I_CGROUPWB flag whose concatenated and abbreviated name is for
consistency with other super_block flags.
ext2_fill_super() is updated to set SB_I_CGROUPWB.
v2: Added super_block->s_iflags instead of stealing another high bit
from sb->s_flags as suggested by Christoph and Jan.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Jan Kara <jack@suse.cz>
Cc: linux-ext4@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b5e1dcf..2c5e33a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1241,6 +1241,8 @@
#define UMOUNT_NOFOLLOW 0x00000008 /* Don't follow symlink on umount */
#define UMOUNT_UNUSED 0x80000000 /* Flag guaranteed to be unused */
+/* sb->s_iflags */
+#define SB_I_CGROUPWB 0x00000001 /* cgroup-aware writeback enabled */
/* Possible states of 'frozen' field */
enum {
@@ -1279,6 +1281,7 @@
const struct quotactl_ops *s_qcop;
const struct export_operations *s_export_op;
unsigned long s_flags;
+ unsigned long s_iflags; /* internal SB_I_* flags */
unsigned long s_magic;
struct dentry *s_root;
struct rw_semaphore s_umount;
@@ -1912,7 +1915,6 @@
#define FS_HAS_SUBTYPE 4
#define FS_USERNS_MOUNT 8 /* Can be mounted by userns root */
#define FS_USERNS_DEV_MOUNT 16 /* A userns mount does not imply MNT_NODEV */
-#define FS_CGROUP_WRITEBACK 32 /* Supports cgroup-aware writeback */
#define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() during rename() internally. */
struct dentry *(*mount) (struct file_system_type *, int,
const char *, void *);