xfs: improve FSGROWFSRT precondition checking

Improve the checking at the start of a realtime grow operation so that
we avoid accidentally set a new extent size that is too large and avoid
adding an rt volume to a filesystem with rmap or reflink because we
don't support rt rmap or reflink yet.

While we're at it, separate the checks so that we're only testing one
aspect at a time.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/xfs_rtalloc.c

@@ -923,16 +923,41 @@ xfs_growfs_rt(
 	uint8_t		*rsum_cache;	/* old summary cache */
 
 	sbp = &mp->m_sb;
-	/*
-	 * Initial error checking.
-	 */
+
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
-	if (mp->m_rtdev_targp == NULL || mp->m_rbmip == NULL ||
-	    (nrblocks = in->newblocks) <= sbp->sb_rblocks ||
-	    (sbp->sb_rblocks && (in->extsize != sbp->sb_rextsize)))
+
+	/* Needs to have been mounted with an rt device. */
+	if (!XFS_IS_REALTIME_MOUNT(mp))
+		return -EINVAL;
+	/*
+	 * Mount should fail if the rt bitmap/summary files don't load, but
+	 * we'll check anyway.
+	 */
+	if (!mp->m_rbmip || !mp->m_rsumip)
+		return -EINVAL;
+
+	/* Shrink not supported. */
+	if (in->newblocks <= sbp->sb_rblocks)
+		return -EINVAL;
+
+	/* Can only change rt extent size when adding rt volume. */
+	if (sbp->sb_rblocks > 0 && in->extsize != sbp->sb_rextsize)
+		return -EINVAL;
+
+	/* Range check the extent size. */
+	if (XFS_FSB_TO_B(mp, in->extsize) > XFS_MAX_RTEXTSIZE ||
+	    XFS_FSB_TO_B(mp, in->extsize) < XFS_MIN_RTEXTSIZE)
 		return -EINVAL;
-	if ((error = xfs_sb_validate_fsb_count(sbp, nrblocks)))
+
+	/* Unsupported realtime features. */
+	if (xfs_sb_version_hasrmapbt(&mp->m_sb) ||
+	    xfs_sb_version_hasreflink(&mp->m_sb))
+		return -EOPNOTSUPP;
+
+	nrblocks = in->newblocks;
+	error = xfs_sb_validate_fsb_count(sbp, nrblocks);
+	if (error)
 		return error;
 	/*
 	 * Read in the last block of the device, make sure it exists.