[PATCH V4 1/8] null_blk: allow REQ_OP_WRITE_ZEROES

Chaitanya Kulkarni
2022-11-29T23:28:49Z

Add a helper function to enable the REQ_OP_WRITE_ZEROES operations
when null_blk.

Since write-zeroes is a non-trivial I/O operation we need this to
add a blktest so we can test the non-trivial I/O path from the
application to the block layer.

Signed-off-by: Chaitanya Kulkarni <kch@nvidia.com>
---
drivers/block/null_blk/main.c | 59 ++++++++++++++++++++++++++++++-
drivers/block/null_blk/null_blk.h | 1 +
2 files changed, 59 insertions(+), 1 deletion(-)

diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index 1f154f92f4c2..2d592b4eb815 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -209,6 +209,10 @@ static bool g_discard;
module_param_named(discard, g_discard, bool, 0444);
MODULE_PARM_DESC(discard, "Support discard operations (requires memory-backed null_blk device). Default: false");

+static bool g_write_zeroes;
+module_param_named(write_zeroes, g_write_zeroes, bool, 0444);
+MODULE_PARM_DESC(write_zeroes, "Support write-zeores operations. Default: false");
+
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)");
@@ -416,6 +420,7 @@ NULLB_DEVICE_ATTR(blocking, bool, NULL);
NULLB_DEVICE_ATTR(use_per_node_hctx, bool, NULL);
NULLB_DEVICE_ATTR(memory_backed, bool, NULL);
NULLB_DEVICE_ATTR(discard, bool, NULL);
+NULLB_DEVICE_ATTR(write_zeroes, bool, NULL);
NULLB_DEVICE_ATTR(mbps, uint, NULL);
NULLB_DEVICE_ATTR(cache_size, ulong, NULL);
NULLB_DEVICE_ATTR(zoned, bool, NULL);
@@ -540,6 +545,7 @@ static struct configfs_attribute *nullb_device_attrs[] = {
&nullb_device_attr_power,
&nullb_device_attr_memory_backed,
&nullb_device_attr_discard,
+ &nullb_device_attr_write_zeroes,
&nullb_device_attr_mbps,
&nullb_device_attr_cache_size,
&nullb_device_attr_badblocks,
@@ -614,7 +620,7 @@ static ssize_t memb_group_features_show(struct config_item *item, char *page)
"poll_queues,power,queue_mode,shared_tag_bitmap,size,"
"submit_queues,use_per_node_hctx,virt_boundary,zoned,"
"zone_capacity,zone_max_active,zone_max_open,"
- "zone_nr_conv,zone_size\n");
+ "zone_nr_conv,zone_size,write_zeroes\n");
}

CONFIGFS_ATTR_RO(memb_group_, features);
@@ -678,6 +684,7 @@ static struct nullb_device *null_alloc_dev(void)
dev->blocking = g_blocking;
dev->memory_backed = g_memory_backed;
dev->discard = g_discard;
+ dev->write_zeroes = g_write_zeroes;
dev->cache_size = g_cache_size;
dev->mbps = g_mbps;
dev->use_per_node_hctx = g_use_per_node_hctx;
@@ -870,6 +877,24 @@ static void null_free_sector(struct nullb *nullb, sector_t sector,
}
}

+static void null_zero_sector(struct nullb_device *d, sector_t sect,
+ sector_t nr_sects, bool cache)
+{
+ struct radix_tree_root *root = cache ? &d->cache : &d->data;
+ struct nullb_page *t_page;
+ unsigned int offset;
+ void *dest;
+
+ t_page = radix_tree_lookup(root, sect >> PAGE_SECTORS_SHIFT);
+ if (!t_page)
+ return;
+
+ offset = (sect & SECTOR_MASK) << SECTOR_SHIFT;
+ dest = kmap_atomic(t_page->page);
+ memset(dest + offset, 0, SECTOR_SIZE * nr_sects);
+ kunmap_atomic(dest);
+}
+
static struct nullb_page *null_radix_tree_insert(struct nullb *nullb, u64 idx,
struct nullb_page *t_page, bool is_cache)
{
@@ -1186,6 +1211,27 @@ blk_status_t null_handle_discard(struct nullb_device *dev,
return BLK_STS_OK;
}

+static blk_status_t null_handle_write_zeroes(struct nullb_device *dev,
+ sector_t sector, sector_t nr_sectors)
+{
+ unsigned int bytes_left = nr_sectors << 9;
+ struct nullb *nullb = dev->nullb;
+ size_t curr_bytes;
+
+ spin_lock_irq(&nullb->lock);
+ while (bytes_left > 0) {
+ curr_bytes = min_t(size_t, bytes_left, nullb->dev->blocksize);
+ nr_sectors = curr_bytes >> SECTOR_SHIFT;
+ null_zero_sector(nullb->dev, sector, nr_sectors, false);
+ if (null_cache_active(nullb))
+ null_zero_sector(nullb->dev, sector, nr_sectors, true);
+ sector += nr_sectors;
+ bytes_left -= curr_bytes;
+ }
+ spin_unlock_irq(&nullb->lock);
+ return BLK_STS_OK;
+}
+
static int null_handle_flush(struct nullb *nullb)
{
int err;
@@ -1352,6 +1398,9 @@ static inline blk_status_t null_handle_memory_backed(struct nullb_cmd *cmd,
if (op == REQ_OP_DISCARD)
return null_handle_discard(dev, sector, nr_sectors);

+ if (op == REQ_OP_WRITE_ZEROES)
+ return null_handle_write_zeroes(dev, sector, nr_sectors);
+
if (dev->queue_mode == NULL_Q_BIO)
err = null_handle_bio(cmd);
else
@@ -1800,6 +1849,13 @@ static void null_config_discard(struct nullb *nullb)
blk_queue_max_discard_sectors(nullb->q, UINT_MAX >> 9);
}

+static void null_config_write_zeroes(struct nullb *nullb)
+{
+ if (!nullb->dev->write_zeroes)
+ return;
+ blk_queue_max_write_zeroes_sectors(nullb->q, UINT_MAX >> 9);
+}
+
static const struct block_device_operations null_bio_ops = {
.owner = THIS_MODULE,
.submit_bio = null_submit_bio,
@@ -2111,6 +2167,7 @@ static int null_add_dev(struct nullb_device *dev)
blk_queue_virt_boundary(nullb->q, PAGE_SIZE - 1);

null_config_discard(nullb);
+ null_config_write_zeroes(nullb);

if (config_item_name(&dev->item)) {
/* Use configfs dir name as the device name */
diff --git a/drivers/block/null_blk/null_blk.h b/drivers/block/null_blk/null_blk.h
index 94ff68052b1e..2c0c9c29158f 100644
--- a/drivers/block/null_blk/null_blk.h
+++ b/drivers/block/null_blk/null_blk.h
@@ -111,6 +111,7 @@ struct nullb_device {
bool power; /* power on/off the device */
bool memory_backed; /* if data is stored in memory */
bool discard; /* if support discard */
+ bool write_zeroes; /* if support write_zeroes */
bool zoned; /* if device is zoned */
bool virt_boundary; /* virtual boundary on/off for the device */
bool no_sched; /* no IO scheduler for the device */
--
2.29.0