[PATCH 6.18 037/314] zloop: advertise a volatile write cache

Sasha Levin
2026-03-10T11:25:14Z

From: Christoph Hellwig <hch@lst.de>

[ Upstream commit 6acf7860dcc79ed045cc9e6a79c8a8bb6959dba7 ]

Zloop is file system backed and thus needs to sync the underlying file
system to persist data. Set BLK_FEAT_WRITE_CACHE so that the block
layer actually send flush commands, and fix the flush implementation
as sync_filesystem requires s_umount to be held and the code currently
misses that.

Fixes: eb0570c7df23 ("block: new zoned loop block device driver")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/block/zloop.c | 24 ++++++++++++++++++------
1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/drivers/block/zloop.c b/drivers/block/zloop.c
index 39a425db670c8..2419677524453 100644
--- a/drivers/block/zloop.c
+++ b/drivers/block/zloop.c
@@ -499,6 +499,21 @@ static void zloop_rw(struct zloop_cmd *cmd)
zloop_put_cmd(cmd);
}

+/*
+ * Sync the entire FS containing the zone files instead of walking all files.
+ */
+static int zloop_flush(struct zloop_device *zlo)
+{
+ struct super_block *sb = file_inode(zlo->data_dir)->i_sb;
+ int ret;
+
+ down_read(&sb->s_umount);
+ ret = sync_filesystem(sb);
+ up_read(&sb->s_umount);
+
+ return ret;
+}
+
static void zloop_handle_cmd(struct zloop_cmd *cmd)
{
struct request *rq = blk_mq_rq_from_pdu(cmd);
@@ -515,11 +530,7 @@ static void zloop_handle_cmd(struct zloop_cmd *cmd)
zloop_rw(cmd);
return;
case REQ_OP_FLUSH:
- /*
- * Sync the entire FS containing the zone files instead of
- * walking all files
- */
- cmd->ret = sync_filesystem(file_inode(zlo->data_dir)->i_sb);
+ cmd->ret = zloop_flush(zlo);
break;
case REQ_OP_ZONE_RESET:
cmd->ret = zloop_reset_zone(zlo, rq_zone_no(rq));
@@ -892,7 +903,8 @@ static int zloop_ctl_add(struct zloop_options *opts)
.max_hw_sectors = SZ_1M >> SECTOR_SHIFT,
.max_hw_zone_append_sectors = SZ_1M >> SECTOR_SHIFT,
.chunk_sectors = opts->zone_size,
- .features = BLK_FEAT_ZONED,
+ .features = BLK_FEAT_ZONED | BLK_FEAT_WRITE_CACHE,
+
};
unsigned int nr_zones, i, j;
struct zloop_device *zlo;
--
2.51.0