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Date:   Fri, 23 Aug 2019 09:55:26 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@redhat.com>
To:     Zhang Tao <kontais@zoho.com>
cc:     agk@redhat.com, snitzer@redhat.com,
        Zhang Tao <zhangtao27@lenovo.com>, dm-devel@redhat.com,
        linux-kernel@vger.kernel.org
Subject: [PATCH 2/2] dm: make dm_table_find_target return NULL
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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>

---
 drivers/md/dm-ioctl.c |    2 +-
 drivers/md/dm-table.c |    8 +++-----
 drivers/md/dm.c       |    8 ++++----
 drivers/md/dm.h       |    5 -----
 4 files changed, 8 insertions(+), 15 deletions(-)

Index: linux-2.6/drivers/md/dm.c
===================================================================
--- linux-2.6.orig/drivers/md/dm.c	2019-08-23 15:45:46.000000000 +0200
+++ linux-2.6/drivers/md/dm.c	2019-08-23 15:45:46.000000000 +0200
@@ -457,7 +457,7 @@ static int dm_blk_report_zones(struct ge
 		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
 		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
 	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 ma
 
 	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;
 		}
Index: linux-2.6/drivers/md/dm-ioctl.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-ioctl.c	2019-08-23 15:45:46.000000000 +0200
+++ linux-2.6/drivers/md/dm-ioctl.c	2019-08-23 15:45:46.000000000 +0200
@@ -1592,7 +1592,7 @@ static int target_message(struct file *f
 	}
 
 	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)
Index: linux-2.6/drivers/md/dm-table.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-table.c	2019-08-23 15:45:46.000000000 +0200
+++ linux-2.6/drivers/md/dm-table.c	2019-08-23 15:47:18.000000000 +0200
@@ -163,10 +163,8 @@ static int alloc_targets(struct dm_table
 
 	/*
 	 * 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(st
 /*
  * 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(s
 	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);
Index: linux-2.6/drivers/md/dm.h
===================================================================
--- linux-2.6.orig/drivers/md/dm.h	2019-08-23 15:45:46.000000000 +0200
+++ linux-2.6/drivers/md/dm.h	2019-08-23 15:45:46.000000000 +0200
@@ -86,11 +86,6 @@ struct target_type *dm_get_immutable_tar
 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).
  */
 #define dm_target_bio_based(t) ((t)->type->map != NULL)