[PATCH 2/3] vfs, writeback: replace FS_CGROUP_WRITEBACK with MS_CGROUPWB

[PATCH 2/3] vfs, writeback: replace FS_CGROUP_WRITEBACK with MS_CGROUPWB

[Tejun Heo]

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 <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Cc: Alexander Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
Cc: linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Cc: Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>
Cc: linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
---
 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

Re: [PATCH 2/3] vfs, writeback: replace FS_CGROUP_WRITEBACK with MS_CGROUPWB

[Christoph Hellwig]

On Fri, Jun 12, 2015 at 04:57:33PM -0500, Tejun Heo wrote:
> 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.

Nak.  As the uapi part makes it obvious the MS_ namespace is part
of the userspace ABI.  Please add a new in-kernel flags field instead.

Re: [PATCH 2/3] vfs, writeback: replace FS_CGROUP_WRITEBACK with MS_CGROUPWB

[Tejun Heo]

Hello, Christoph.

On Sat, Jun 13, 2015 at 09:16:08AM -0700, Christoph Hellwig wrote:
> On Fri, Jun 12, 2015 at 04:57:33PM -0500, Tejun Heo wrote:
> > 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.
> 
> Nak.  As the uapi part makes it obvious the MS_ namespace is part
> of the userspace ABI.  Please add a new in-kernel flags field instead.

Are MS_ACTIVE and MS_BORN part of userpace ABI?  They seem pretty
internal.  I don't mind introducing a new internal flag field but it's
weird to put this single flag there with other internal flags in
->s_flags.

Assuming we add a new field, how do sb->s_iflags and SB_I_XXX sound?
Any better suggestions?

Thanks.

-- 
tejun

Re: [PATCH 2/3] vfs, writeback: replace FS_CGROUP_WRITEBACK with MS_CGROUPWB

[Jan Kara]

On Sun 14-06-15 00:42:36, Tejun Heo wrote:
> Hello, Christoph.
> 
> On Sat, Jun 13, 2015 at 09:16:08AM -0700, Christoph Hellwig wrote:
> > On Fri, Jun 12, 2015 at 04:57:33PM -0500, Tejun Heo wrote:
> > > 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.
> > 
> > Nak.  As the uapi part makes it obvious the MS_ namespace is part
> > of the userspace ABI.  Please add a new in-kernel flags field instead.
> 
> Are MS_ACTIVE and MS_BORN part of userpace ABI?  They seem pretty
> internal.  I don't mind introducing a new internal flag field but it's
> weird to put this single flag there with other internal flags in
> ->s_flags.
  So you are right that there are other internal flags allocated from the
top of the i_flags field, however we are pretty much running out of the
flags available for the ABI so it's better to move internal flags elsewhere
as that's simpler than creating a new ABI for mount...

> Assuming we add a new field, how do sb->s_iflags and SB_I_XXX sound?
> Any better suggestions?
  Looks good to me.

								Honza
-- 
Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>
SUSE Labs, CR