[PATCH 9/9] xfs: allow bulkstat_single of special inodes

["Darrick J. Wong" <darrick.wong@oracle.com>]

From: Darrick J. Wong <darrick.wong@oracle.com>

Create a new ireq flag (for single bulkstats) that enables userspace to
ask us for a special inode number instead of interpreting @ino as a
literal inode number.  This enables us to query the root inode easily.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Allison Collins <allison.henderson@oracle.com>
---
 fs/xfs/libxfs/xfs_fs.h |   11 ++++++++++-
 fs/xfs/xfs_ioctl.c     |   10 ++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)


diff --git a/fs/xfs/libxfs/xfs_fs.h b/fs/xfs/libxfs/xfs_fs.h
index 77c06850ac52..1489bce07d66 100644
--- a/fs/xfs/libxfs/xfs_fs.h
+++ b/fs/xfs/libxfs/xfs_fs.h
@@ -482,7 +482,16 @@ struct xfs_ireq {
 	uint64_t	reserved[2];	/* must be zero			*/
 };
 
-#define XFS_IREQ_FLAGS_ALL	(0)
+/*
+ * The @ino value is a special value, not a literal inode number.  See the
+ * XFS_IREQ_SPECIAL_* values below.
+ */
+#define XFS_IREQ_SPECIAL	(1 << 0)
+
+#define XFS_IREQ_FLAGS_ALL	(XFS_IREQ_SPECIAL)
+
+/* Operate on the root directory inode. */
+#define XFS_IREQ_SPECIAL_ROOT	(1)
 
 /*
  * ioctl structures for v5 bulkstat and inumbers requests
diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index f71341cd8340..3bb5f980fabf 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -961,6 +961,16 @@ xfs_ireq_setup(
 	    memchr_inv(hdr->reserved, 0, sizeof(hdr->reserved)))
 		return -EINVAL;
 
+	if (hdr->flags & XFS_IREQ_SPECIAL) {
+		switch (hdr->ino) {
+		case XFS_IREQ_SPECIAL_ROOT:
+			hdr->ino = mp->m_sb.sb_rootino;
+			break;
+		default:
+			return -EINVAL;
+		}
+	}
+
 	if (XFS_INO_TO_AGNO(mp, hdr->ino) >= mp->m_sb.sb_agcount)
 		return -EINVAL;