[PATCH v2 18/28] null_blk: Introduce fua attribute

Damien Le Moal
2024-03-25T04:45:30Z

Add the fua configfs attribute and module parameter to allow
configuring if the device supports FUA or not. Using this attribute
has an effect on the null_blk device only if memory backing is enabled
together with a write cache (cache_size option).

This new attribute allows configuring a null_blk device with a write
cache but without FUA support. This is convenient to test the block
layer flush machinery.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
---
drivers/block/null_blk/main.c | 12 ++++++++++--
drivers/block/null_blk/null_blk.h | 1 +
2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index cd6519360dbc..47e1bbb5b24e 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -225,6 +225,10 @@ static unsigned long g_cache_size;
module_param_named(cache_size, g_cache_size, ulong, 0444);
MODULE_PARM_DESC(mbps, "Cache size in MiB for memory-backed device. Default: 0 (none)");

+static bool g_fua = true;
+module_param_named(fua, g_fua, bool, S_IRUGO);
+MODULE_PARM_DESC(zoned, "Enable/disable FUA support when cache_size is used. Default: true");
+
static unsigned int g_mbps;
module_param_named(mbps, g_mbps, uint, 0444);
MODULE_PARM_DESC(mbps, "Limit maximum bandwidth (in MiB/s). Default: 0 (no limit)");
@@ -446,6 +450,7 @@ NULLB_DEVICE_ATTR(virt_boundary, bool, NULL);
NULLB_DEVICE_ATTR(no_sched, bool, NULL);
NULLB_DEVICE_ATTR(shared_tags, bool, NULL);
NULLB_DEVICE_ATTR(shared_tag_bitmap, bool, NULL);
+NULLB_DEVICE_ATTR(fua, bool, NULL);

static ssize_t nullb_device_power_show(struct config_item *item, char *page)
{
@@ -593,6 +598,7 @@ static struct configfs_attribute *nullb_device_attrs[] = {
&nullb_device_attr_no_sched,
&nullb_device_attr_shared_tags,
&nullb_device_attr_shared_tag_bitmap,
+ &nullb_device_attr_fua,
NULL,
};

@@ -671,7 +677,7 @@ nullb_group_drop_item(struct config_group *group, struct config_item *item)
static ssize_t memb_group_features_show(struct config_item *item, char *page)
{
return snprintf(page, PAGE_SIZE,
- "badblocks,blocking,blocksize,cache_size,"
+ "badblocks,blocking,blocksize,cache_size,fua,"
"completion_nsec,discard,home_node,hw_queue_depth,"
"irqmode,max_sectors,mbps,memory_backed,no_sched,"
"poll_queues,power,queue_mode,shared_tag_bitmap,"
@@ -763,6 +769,8 @@ static struct nullb_device *null_alloc_dev(void)
dev->no_sched = g_no_sched;
dev->shared_tags = g_shared_tags;
dev->shared_tag_bitmap = g_shared_tag_bitmap;
+ dev->fua = g_fua;
+
return dev;
}

@@ -1920,7 +1928,7 @@ static int null_add_dev(struct nullb_device *dev)

if (dev->cache_size > 0) {
set_bit(NULLB_DEV_FL_CACHE, &nullb->dev->flags);
- blk_queue_write_cache(nullb->q, true, true);
+ blk_queue_write_cache(nullb->q, true, dev->fua);
}

nullb->q->queuedata = nullb;
diff --git a/drivers/block/null_blk/null_blk.h b/drivers/block/null_blk/null_blk.h
index a9c5df650ddb..3234e6c85eed 100644
--- a/drivers/block/null_blk/null_blk.h
+++ b/drivers/block/null_blk/null_blk.h
@@ -105,6 +105,7 @@ struct nullb_device {
bool no_sched; /* no IO scheduler for the device */
bool shared_tags; /* share tag set between devices for blk-mq */
bool shared_tag_bitmap; /* use hostwide shared tags */
+ bool fua; /* Support FUA */
};

struct nullb {
--
2.44.0