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
kernel-internal super_block->s_flags MS_CGROUPWB.  The concatenated
and abbreviated name is for consistency with other MS_* flags.

ext2_fill_super() is updated to assert MS_CGROUPWB.

Signed-off-by: Tejun Heo <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: [email protected]
Cc: Jan Kara <[email protected]>
Cc: [email protected]
---
 fs/ext2/super.c             | 4 ++--
 fs/namespace.c              | 2 +-
 include/linux/backing-dev.h | 2 +-
 include/linux/fs.h          | 1 -
 include/uapi/linux/fs.h     | 1 +
 5 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/ext2/super.c b/fs/ext2/super.c
index 549219d..472ed34 100644
--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c
@@ -879,7 +879,7 @@ static int ext2_fill_super(struct super_block *sb, void 
*data, int silent)
        if (!parse_options((char *) data, sb))
                goto failed_mount;
 
-       sb->s_flags = (sb->s_flags & ~MS_POSIXACL) |
+       sb->s_flags = (sb->s_flags & ~MS_POSIXACL) | MS_CGROUPWB |
                ((EXT2_SB(sb)->s_mount_opt & EXT2_MOUNT_POSIX_ACL) ?
                 MS_POSIXACL : 0);
 
@@ -1543,7 +1543,7 @@ static struct file_system_type ext2_fs_type = {
        .name           = "ext2",
        .mount          = ext2_mount,
        .kill_sb        = kill_block_super,
-       .fs_flags       = FS_REQUIRES_DEV | FS_CGROUP_WRITEBACK,
+       .fs_flags       = FS_REQUIRES_DEV,
 };
 MODULE_ALIAS_FS("ext2");
 
diff --git a/fs/namespace.c b/fs/namespace.c
index 1f4f9da..507b90b 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2669,7 +2669,7 @@ long do_mount(const char *dev_name, const char __user 
*dir_name,
 
        flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | MS_BORN |
                   MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT |
-                  MS_STRICTATIME);
+                  MS_STRICTATIME | MS_CGROUPWB);
 
        if (flags & MS_REMOUNT)
                retval = do_remount(&path, flags & ~MS_REMOUNT, mnt_flags,
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index dfce808..1489131 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -260,7 +260,7 @@ static inline bool inode_cgwb_enabled(struct inode *inode)
 
        return bdi_cap_account_dirty(bdi) &&
                (bdi->capabilities & BDI_CAP_CGROUP_WRITEBACK) &&
-               (inode->i_sb->s_type->fs_flags & FS_CGROUP_WRITEBACK);
+               (inode->i_sb->s_flags & MS_CGROUPWB);
 }
 
 /**
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b5e1dcf..66e35dc 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1912,7 +1912,6 @@ struct file_system_type {
 #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 *);
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index 9b964a5..60316e7 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -93,6 +93,7 @@ struct inodes_stat_t {
 #define MS_LAZYTIME    (1<<25) /* Update the on-disk [acm]times lazily */
 
 /* These sb flags are internal to the kernel */
+#define MS_CGROUPWB    (1<<27) /* cgroup-aware writeback enabled */
 #define MS_NOSEC       (1<<28)
 #define MS_BORN                (1<<29)
 #define MS_ACTIVE      (1<<30)
-- 
2.4.2

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