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/fs/ext2/super.c b/fs/ext2/super.c
index 549219d44f1c1231db1215b092544bdfe7503fde..900e19cf9ef6fbb4057e95f2cc1f81c44ccd3377 100644 (file)
--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c
@@ -882,6 +882,7 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
        sb->s_flags = (sb->s_flags & ~MS_POSIXACL) |
                ((EXT2_SB(sb)->s_mount_opt & EXT2_MOUNT_POSIX_ACL) ?
                 MS_POSIXACL : 0);
+       sb->s_iflags |= SB_I_CGROUPWB;
 
        if (le32_to_cpu(es->s_rev_level) == EXT2_GOOD_OLD_REV &&
            (EXT2_HAS_COMPAT_FEATURE(sb, ~0U) ||
@@ -1543,7 +1544,7 @@ 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/include/linux/backing-dev.h b/include/linux/backing-dev.h
index dfce808691450c9fd83ece6f608fc797bef5fbdb..a13181a42b9aee87a652d1a94a7e322dc6aaaf6e 100644 (file)
--- 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_iflags & SB_I_CGROUPWB);
 }
 
 /**

diff --git a/include/linux/fs.h b/include/linux/fs.h
index b5e1dcfbc5e36c8756dbe7d8b0e2e8f29823e987..2c5e33a5b2af4af5934597b082452858d7717f28 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1241,6 +1241,8 @@ struct mm_struct;
 #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 @@ struct super_block {
        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 @@ 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 *);