xfs: explicitly initialize meta_scrub_ops array by type

An implicit mapping to type by order of initialization seems
error-prone, and doesn't lend itself to cscope-ing.

Also add sanity checks about size of array vs. max types,
and a defensive check that ->scrub exists before using it.
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/scrub/scrub.c

@@ -167,104 +167,104 @@ xfs_scrub_teardown(
 /* Scrubbing dispatch. */
 
 static const struct xfs_scrub_meta_ops meta_scrub_ops[] = {
-	{ /* ioctl presence test */
+	[XFS_SCRUB_TYPE_PROBE] = {	/* ioctl presence test */
 		.setup	= xfs_scrub_setup_fs,
 		.scrub	= xfs_scrub_probe,
 	},
-	{ /* superblock */
+	[XFS_SCRUB_TYPE_SB] = {		/* superblock */
 		.setup	= xfs_scrub_setup_ag_header,
 		.scrub	= xfs_scrub_superblock,
 	},
-	{ /* agf */
+	[XFS_SCRUB_TYPE_AGF] = {	/* agf */
 		.setup	= xfs_scrub_setup_ag_header,
 		.scrub	= xfs_scrub_agf,
 	},
-	{ /* agfl */
+	[XFS_SCRUB_TYPE_AGFL]= {	/* agfl */
 		.setup	= xfs_scrub_setup_ag_header,
 		.scrub	= xfs_scrub_agfl,
 	},
-	{ /* agi */
+	[XFS_SCRUB_TYPE_AGI] = {	/* agi */
 		.setup	= xfs_scrub_setup_ag_header,
 		.scrub	= xfs_scrub_agi,
 	},
-	{ /* bnobt */
+	[XFS_SCRUB_TYPE_BNOBT] = {	/* bnobt */
 		.setup	= xfs_scrub_setup_ag_allocbt,
 		.scrub	= xfs_scrub_bnobt,
 	},
-	{ /* cntbt */
+	[XFS_SCRUB_TYPE_CNTBT] = {	/* cntbt */
 		.setup	= xfs_scrub_setup_ag_allocbt,
 		.scrub	= xfs_scrub_cntbt,
 	},
-	{ /* inobt */
+	[XFS_SCRUB_TYPE_INOBT] = {	/* inobt */
 		.setup	= xfs_scrub_setup_ag_iallocbt,
 		.scrub	= xfs_scrub_inobt,
 	},
-	{ /* finobt */
+	[XFS_SCRUB_TYPE_FINOBT] = {	/* finobt */
 		.setup	= xfs_scrub_setup_ag_iallocbt,
 		.scrub	= xfs_scrub_finobt,
 		.has	= xfs_sb_version_hasfinobt,
 	},
-	{ /* rmapbt */
+	[XFS_SCRUB_TYPE_RMAPBT] = {	/* rmapbt */
 		.setup	= xfs_scrub_setup_ag_rmapbt,
 		.scrub	= xfs_scrub_rmapbt,
 		.has	= xfs_sb_version_hasrmapbt,
 	},
-	{ /* refcountbt */
+	[XFS_SCRUB_TYPE_REFCNTBT] = {	/* refcountbt */
 		.setup	= xfs_scrub_setup_ag_refcountbt,
 		.scrub	= xfs_scrub_refcountbt,
 		.has	= xfs_sb_version_hasreflink,
 	},
-	{ /* inode record */
+	[XFS_SCRUB_TYPE_INODE] = {	/* inode record */
 		.setup	= xfs_scrub_setup_inode,
 		.scrub	= xfs_scrub_inode,
 	},
-	{ /* inode data fork */
+	[XFS_SCRUB_TYPE_BMBTD] = {	/* inode data fork */
 		.setup	= xfs_scrub_setup_inode_bmap,
 		.scrub	= xfs_scrub_bmap_data,
 	},
-	{ /* inode attr fork */
+	[XFS_SCRUB_TYPE_BMBTA] = {	/* inode attr fork */
 		.setup	= xfs_scrub_setup_inode_bmap,
 		.scrub	= xfs_scrub_bmap_attr,
 	},
-	{ /* inode CoW fork */
+	[XFS_SCRUB_TYPE_BMBTC] = {	/* inode CoW fork */
 		.setup	= xfs_scrub_setup_inode_bmap,
 		.scrub	= xfs_scrub_bmap_cow,
 	},
-	{ /* directory */
+	[XFS_SCRUB_TYPE_DIR] = {	/* directory */
 		.setup	= xfs_scrub_setup_directory,
 		.scrub	= xfs_scrub_directory,
 	},
-	{ /* extended attributes */
+	[XFS_SCRUB_TYPE_XATTR] = {	/* extended attributes */
 		.setup	= xfs_scrub_setup_xattr,
 		.scrub	= xfs_scrub_xattr,
 	},
-	{ /* symbolic link */
+	[XFS_SCRUB_TYPE_SYMLINK] = {	/* symbolic link */
 		.setup	= xfs_scrub_setup_symlink,
 		.scrub	= xfs_scrub_symlink,
 	},
-	{ /* parent pointers */
+	[XFS_SCRUB_TYPE_PARENT] = {	/* parent pointers */
 		.setup	= xfs_scrub_setup_parent,
 		.scrub	= xfs_scrub_parent,
 	},
-	{ /* realtime bitmap */
+	[XFS_SCRUB_TYPE_RTBITMAP] = {	/* realtime bitmap */
 		.setup	= xfs_scrub_setup_rt,
 		.scrub	= xfs_scrub_rtbitmap,
 		.has	= xfs_sb_version_hasrealtime,
 	},
-	{ /* realtime summary */
+	[XFS_SCRUB_TYPE_RTSUM] = {	/* realtime summary */
 		.setup	= xfs_scrub_setup_rt,
 		.scrub	= xfs_scrub_rtsummary,
 		.has	= xfs_sb_version_hasrealtime,
 	},
-	{ /* user quota */
+	[XFS_SCRUB_TYPE_UQUOTA] = {	/* user quota */
 		.setup = xfs_scrub_setup_quota,
 		.scrub = xfs_scrub_quota,
 	},
-	{ /* group quota */
+	[XFS_SCRUB_TYPE_GQUOTA] = {	/* group quota */
 		.setup = xfs_scrub_setup_quota,
 		.scrub = xfs_scrub_quota,
 	},
-	{ /* project quota */
+	[XFS_SCRUB_TYPE_PQUOTA] = {	/* project quota */
 		.setup = xfs_scrub_setup_quota,
 		.scrub = xfs_scrub_quota,
 	},
@@ -296,6 +296,9 @@ xfs_scrub_metadata(
 	bool				try_harder = false;
 	int				error = 0;
 
+	BUILD_BUG_ON(sizeof(meta_scrub_ops) !=
+		(sizeof(struct xfs_scrub_meta_ops) * XFS_SCRUB_TYPE_NR));
+
 	trace_xfs_scrub_start(ip, sm, error);
 
 	/* Forbidden if we are shut down or mounted norecovery. */
@@ -319,7 +322,7 @@ xfs_scrub_metadata(
 	if (sm->sm_type >= XFS_SCRUB_TYPE_NR)
 		goto out;
 	ops = &meta_scrub_ops[sm->sm_type];
-	if (ops->scrub == NULL)
+	if (ops->setup == NULL || ops->scrub == NULL)
 		goto out;
 
 	/*