[PATCH v2 1/4] block: Introduce bio_needs_zone_write_plugging()

[Damien Le Moal <dlemoal@kernel.org>]

In preparation for fixing device mapper zone write handling, introduce
the helper function bio_needs_zone_write_plugging() to test if a BIO
requires handling through zone write plugging. This function returns
true for any write operation to a zoned block device. For zone append
opertions, true is returned only if the device requires zone append
emulation with regular writes.

Fixes: f211268ed1f9 ("dm: Use the block layer zone append emulation")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
---
 block/blk-zoned.c      | 40 ++++++++++++++++++++++++++++++++++++++++
 include/linux/blkdev.h |  9 +++++++++
 2 files changed, 49 insertions(+)

diff --git a/block/blk-zoned.c b/block/blk-zoned.c
index 55e64ca869d7..9d38b94cad0d 100644
--- a/block/blk-zoned.c
+++ b/block/blk-zoned.c
@@ -1129,6 +1129,46 @@ static void blk_zone_wplug_handle_native_zone_append(struct bio *bio)
 	disk_put_zone_wplug(zwplug);
 }
 
+/**
+ * bio_needs_zone_write_plugging - Check if a BIO needs to be handled with zone
+ *				   write plugging
+ * @bio: The BIO being submitted
+ *
+ * Return true whenever @bio execution needs to be handled through zone
+ * write plugging. Return false otherwise.
+ */
+bool bio_needs_zone_write_plugging(struct bio *bio)
+{
+	enum req_op op = bio_op(bio);
+
+	if (!bdev_is_zoned(bio->bi_bdev) || !op_is_write(op))
+		return false;
+
+	/* Already handled ? */
+	if (bio_flagged(bio, BIO_ZONE_WRITE_PLUGGING))
+		return false;
+
+	/* Ignore empty flush */
+	if (op_is_flush(bio->bi_opf) && !bio_sectors(bio))
+		return false;
+
+	/*
+	 * Regular writes and write zeroes need to be handled through zone
+	 * write plugging. Zone append operations only need zone write plugging
+	 * if they are emulated.
+	 */
+	switch (op) {
+	case REQ_OP_ZONE_APPEND:
+		return bdev_emulates_zone_append(bio->bi_bdev);
+	case REQ_OP_WRITE:
+	case REQ_OP_WRITE_ZEROES:
+		return true;
+	default:
+		return false;
+	}
+}
+EXPORT_SYMBOL_GPL(bio_needs_zone_write_plugging);
+
 /**
  * blk_zone_plug_bio - Handle a zone write BIO with zone write plugging
  * @bio: The BIO being submitted
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index c2b3ddea8b6d..d455057bfaa3 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -848,6 +848,9 @@ static inline unsigned int disk_nr_zones(struct gendisk *disk)
 {
 	return disk->nr_zones;
 }
+
+bool bio_needs_zone_write_plugging(struct bio *bio);
+
 bool blk_zone_plug_bio(struct bio *bio, unsigned int nr_segs);
 
 /**
@@ -877,6 +880,12 @@ static inline unsigned int disk_nr_zones(struct gendisk *disk)
 {
 	return 0;
 }
+
+static inline bool bio_needs_zone_write_plugging(struct bio *bio)
+{
+	return false;
+}
+
 static inline bool blk_zone_plug_bio(struct bio *bio, unsigned int nr_segs)
 {
 	return false;
-- 
2.49.0