[PATCH v7 1/3] xfs: Show realtime device stats on statfs calls if realtime flags set

[Richard Wareing <rwareing@fb.com>]

- Reports realtime device free blocks in statfs calls if (realtime)
  inheritance bit is set on the inode of directory, or realtime flag
  in the case of files.  This is a bit more intuitive, especially for
  use-cases which are using a much larger device for the realtime device.
- Add XFS_IS_REALTIME_MOUNT option to gate based on the existence of a
  realtime device on the mount, similar to the XFS_IS_REALTIME_INODE
  option.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Richard Wareing <rwareing@fb.com>
---
Changes since v6:
* statfs will now return realtime stats for the underlying filesystem if
inode has XFS_DIFLAG_REALTIME set, this provides consistent behavior along
the same lines as the XFS_DIFLAG_RTINHERIT flag is set on directories.
* Updated commit title + description to reflect change

Changes since v5:
* None

Changes since v4:
* None

Changes since v3:
* Fixed accounting bug, we are not required to substract m_alloc_set_aside
  as this is a data device only requirement.
* Added XFS_IS_REALTIME_MOUNT macro based on learnings from CVE-2017-14340,
  now provides similar gating on the mount as XFS_IS_REALTIME_INODE does
  for the inode.

Changes since v2:
* Style updated per Christoph Hellwig's comment
* Fixed bug: statp->f_bavail = statp->f_bfree

 fs/xfs/xfs_linux.h | 2 ++
 fs/xfs/xfs_super.c | 8 ++++++++
 2 files changed, 10 insertions(+)

diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h
index dcd1292..944b02d 100644
--- a/fs/xfs/xfs_linux.h
+++ b/fs/xfs/xfs_linux.h
@@ -278,8 +278,10 @@ static inline uint64_t howmany_64(uint64_t x, uint32_t y)
 #define XFS_IS_REALTIME_INODE(ip)			\
 	(((ip)->i_d.di_flags & XFS_DIFLAG_REALTIME) &&	\
 	 (ip)->i_mount->m_rtdev_targp)
+#define XFS_IS_REALTIME_MOUNT(mp) ((mp)->m_rtdev_targp ? 1 : 0)
 #else
 #define XFS_IS_REALTIME_INODE(ip) (0)
+#define XFS_IS_REALTIME_MOUNT(mp) (0)
 #endif
 
 #endif /* __XFS_LINUX__ */
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index f663022..07afadd 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1153,6 +1153,14 @@ xfs_fs_statfs(
 	    ((mp->m_qflags & (XFS_PQUOTA_ACCT|XFS_PQUOTA_ENFD))) ==
 			      (XFS_PQUOTA_ACCT|XFS_PQUOTA_ENFD))
 		xfs_qm_statvfs(ip, statp);
+
+	if (XFS_IS_REALTIME_MOUNT(mp) &&
+	    (ip->i_d.di_flags & (XFS_DIFLAG_RTINHERIT | XFS_DIFLAG_REALTIME))) {
+		statp->f_blocks = sbp->sb_rblocks;
+		statp->f_bavail = statp->f_bfree =
+			sbp->sb_frextents * sbp->sb_rextsize;
+	}
+
 	return 0;
 }
 
-- 
2.9.5