[PATCH v4 1/3] xfs: Show realtime device stats on statfs calls if inherit flag set

[Richard Wareing <rwareing@fb.com>]

- Reports realtime device free blocks in statfs calls if inheritance
  bit is set on the inode of directory.  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.

Signed-off-by: Richard Wareing <rwareing@fb.com>
---
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 044fb0e..fe46e71 100644
--- a/fs/xfs/xfs_linux.h
+++ b/fs/xfs/xfs_linux.h
@@ -280,8 +280,10 @@ static inline __uint64_t howmany_64(__uint64_t x, __uint32_t y)
 
 #ifdef CONFIG_XFS_RT
 #define XFS_IS_REALTIME_INODE(ip) ((ip)->i_d.di_flags & XFS_DIFLAG_REALTIME)
+#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 455a575..6d33a5e 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1136,6 +1136,14 @@ 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)) {
+		statp->f_blocks = sbp->sb_rblocks;
+		statp->f_bavail = statp->f_bfree =
+			sbp->sb_frextents * sbp->sb_rextsize;
+	}
+
 	return 0;
 }
 
-- 
2.9.5