[PATCHv2 5/6] zloop: set dma_alignment from the backing files for direct I/O

From: Keith Busch <[email protected]>

Direct I/O request's use pages handed to the backing files unchanged, so
the backing's DMA alignment requirement applies. Track dio_mem_align and
advertise it as the device's dma_alignment so we communicate proper
limits and misaligned I/O is rejected here instead of reaching the
backend.

Signed-off-by: Keith Busch <[email protected]>
---
 drivers/block/zloop.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/drivers/block/zloop.c b/drivers/block/zloop.c
index 55eeb6aac0ea3..1149b817b5bc9 100644
--- a/drivers/block/zloop.c
+++ b/drivers/block/zloop.c
@@ -144,6 +144,7 @@ struct zloop_device {
 	unsigned int		nr_conv_zones;
 	unsigned int		max_open_zones;
 	unsigned int		block_size;
+	unsigned int		dio_mem_align;
 
 	spinlock_t		open_zones_lock;
 	struct list_head	open_zones_lru_list;
@@ -1035,6 +1036,9 @@ static int zloop_get_block_size(struct zloop_device *zlo,
 {
 	struct block_device *sb_bdev = zone->file->f_mapping->host->i_sb->s_bdev;
 	struct kstat st;
+	bool have_dioalign = !vfs_getattr(&zone->file->f_path, &st,
+					  STATX_DIOALIGN, 0) &&
+			     (st.result_mask & STATX_DIOALIGN);
 
 	/*
 	 * If the FS block size is lower than or equal to 4K, use that as the
@@ -1044,14 +1048,25 @@ static int zloop_get_block_size(struct zloop_device *zlo,
 	 */
 	if (file_inode(zone->file)->i_sb->s_blocksize <= SZ_4K)
 		zlo->block_size = file_inode(zone->file)->i_sb->s_blocksize;
-	else if (!vfs_getattr(&zone->file->f_path, &st, STATX_DIOALIGN, 0) &&
-		 (st.result_mask & STATX_DIOALIGN))
+	else if (have_dioalign)
 		zlo->block_size = st.dio_offset_align;
 	else if (sb_bdev)
 		zlo->block_size = bdev_physical_block_size(sb_bdev);
 	else
 		zlo->block_size = SECTOR_SIZE;
 
+	/*
+	 * In direct I/O the request's pages are handed to the backing files
+	 * unchanged, so track their required memory alignment as a mask for
+	 * dma_alignment.
+	 */
+	if (have_dioalign)
+		zlo->dio_mem_align = st.dio_mem_align - 1;
+	else if (sb_bdev)
+		zlo->dio_mem_align = bdev_dma_alignment(sb_bdev);
+	else
+		zlo->dio_mem_align = SECTOR_SIZE - 1;
+
 	if (zlo->zone_capacity & ((zlo->block_size >> SECTOR_SHIFT) - 1)) {
 		pr_err("Zone capacity is not aligned to block size %u\n",
 		       zlo->block_size);
@@ -1279,6 +1294,9 @@ static int zloop_ctl_add(struct zloop_options *opts)
 
 	lim.physical_block_size = zlo->block_size;
 	lim.logical_block_size = zlo->block_size;
+	/* Direct I/O hands the request's pages to the backing files unchanged. */
+	if (!opts->buffered_io)
+		lim.dma_alignment = zlo->dio_mem_align;
 	if (zlo->zone_append)
 		lim.max_hw_zone_append_sectors = lim.max_hw_sectors;
 	lim.max_open_zones = zlo->max_open_zones;
-- 
2.52.0