dm: make dm_table_find_target return NULL

Currently, if we pass too high sector number to dm_table_find_target, it
returns zeroed dm_target structure and callers test if the structure is
zeroed with the macro dm_target_is_valid.

However, returning NULL is common practice to indicate errors.

This patch refactors the dm code, so that dm_table_find_target returns
NULL and its callers test the returned value for NULL. The macro
dm_target_is_valid is deleted. In alloc_targets, we no longer allocate an
extra zeroed target.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-ioctl.c

@@ -1592,7 +1592,7 @@ static int target_message(struct file *filp, struct dm_ioctl *param, size_t para
 	}
 
 	ti = dm_table_find_target(table, tmsg->sector);
-	if (!dm_target_is_valid(ti)) {
+	if (!ti) {
 		DMWARN("Target message sector outside device.");
 		r = -EINVAL;
 	} else if (ti->type->message)

drivers/md/dm-table.c

@@ -163,10 +163,8 @@ static int alloc_targets(struct dm_table *t, unsigned int num)
 
 	/*
 	 * Allocate both the target array and offset array at once.
-	 * Append an empty entry to catch sectors beyond the end of
-	 * the device.
 	 */
-	n_highs = (sector_t *) dm_vcalloc(num + 1, sizeof(struct dm_target) +
+	n_highs = (sector_t *) dm_vcalloc(num, sizeof(struct dm_target) +
 					  sizeof(sector_t));
 	if (!n_highs)
 		return -ENOMEM;
@@ -1359,7 +1357,7 @@ struct dm_target *dm_table_get_target(struct dm_table *t, unsigned int index)
 /*
  * Search the btree for the correct target.
  *
- * Caller should check returned pointer with dm_target_is_valid()
+ * Caller should check returned pointer for NULL
  * to trap I/O beyond end of device.
  */
 struct dm_target *dm_table_find_target(struct dm_table *t, sector_t sector)
@@ -1368,7 +1366,7 @@ struct dm_target *dm_table_find_target(struct dm_table *t, sector_t sector)
 	sector_t *node;
 
 	if (unlikely(sector >= dm_table_get_size(t)))
-		return &t->targets[t->num_targets];
+		return NULL;
 
 	for (l = 0; l < t->depth; l++) {
 		n = get_child(n, k);

drivers/md/dm.c

@@ -457,7 +457,7 @@ static int dm_blk_report_zones(struct gendisk *disk, sector_t sector,
 		return -EIO;
 
 	tgt = dm_table_find_target(map, sector);
-	if (!dm_target_is_valid(tgt)) {
+	if (!tgt) {
 		ret = -EIO;
 		goto out;
 	}
@@ -1072,7 +1072,7 @@ static struct dm_target *dm_dax_get_live_target(struct mapped_device *md,
 		return NULL;
 
 	ti = dm_table_find_target(map, sector);
-	if (!dm_target_is_valid(ti))
+	if (!ti)
 		return NULL;
 
 	return ti;
@@ -1572,7 +1572,7 @@ static int __split_and_process_non_flush(struct clone_info *ci)
 	int r;
 
 	ti = dm_table_find_target(ci->map, ci->sector);
-	if (!dm_target_is_valid(ti))
+	if (!ti)
 		return -EIO;
 
 	if (__process_abnormal_io(ci, ti, &r))
@@ -1748,7 +1748,7 @@ static blk_qc_t dm_process_bio(struct mapped_device *md,
 
 	if (!ti) {
 		ti = dm_table_find_target(map, bio->bi_iter.bi_sector);
-		if (unlikely(!ti || !dm_target_is_valid(ti))) {
+		if (unlikely(!ti)) {
 			bio_io_error(bio);
 			return ret;
 		}

drivers/md/dm.h

@@ -85,11 +85,6 @@ struct target_type *dm_get_immutable_target_type(struct mapped_device *md);
 
 int dm_setup_md_queue(struct mapped_device *md, struct dm_table *t);
 
-/*
- * To check the return value from dm_table_find_target().
- */
-#define dm_target_is_valid(t) ((t)->table)
-
 /*
  * To check whether the target type is bio-based or not (request-based).
  */