[PATCH V2 6/9] nullb: support discard

[Shaohua Li]

From: Shaohua Li <s...@fb.com>

discard makes sense for memory backed disk. And also it's useful to test
if upper layer supports dicard correctly.

User configures 'discard' attribute to enable/disable dicard support.

Based on original patch from Kyungchan Koh

Signed-off-by: Kyungchan Koh <kkc6...@fb.com>
Signed-off-by: Shaohua Li <s...@fb.com>
---
 drivers/block/null_blk.c | 42 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 41 insertions(+), 1 deletion(-)

diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c
index 45e0b56..1f3cf25 100644
--- a/drivers/block/null_blk.c
+++ b/drivers/block/null_blk.c
@@ -88,6 +88,7 @@ struct nullb_device {
        bool use_per_node_hctx; /* use per-node allocation for hardware context 
*/
        bool power; /* power on/off the device */
        bool memory_backed; /* if data is stored in memory */
+       bool discard; /* if support discard */
 };
 
 struct nullb {
@@ -318,6 +319,7 @@ NULLB_DEVICE_ATTR(use_lightnvm, bool);
 NULLB_DEVICE_ATTR(blocking, bool);
 NULLB_DEVICE_ATTR(use_per_node_hctx, bool);
 NULLB_DEVICE_ATTR(memory_backed, bool);
+NULLB_DEVICE_ATTR(discard, bool);
 
 static ssize_t nullb_device_power_show(struct config_item *item, char *page)
 {
@@ -373,6 +375,7 @@ static struct configfs_attribute *nullb_device_attrs[] = {
        &nullb_device_attr_use_per_node_hctx,
        &nullb_device_attr_power,
        &nullb_device_attr_memory_backed,
+       &nullb_device_attr_discard,
        NULL,
 };
 
@@ -425,7 +428,7 @@ 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, "memory_backed\n");
+       return snprintf(page, PAGE_SIZE, "memory_backed,discard\n");
 }
 
 CONFIGFS_ATTR_RO(memb_group_, features);
@@ -815,6 +818,20 @@ static int copy_from_nullb(struct nullb *nullb, struct 
page *dest,
        return 0;
 }
 
+static void null_handle_discard(struct nullb *nullb, sector_t sector, size_t n)
+{
+       size_t temp;
+
+       spin_lock_irq(&nullb->lock);
+       while (n > 0) {
+               temp = min_t(size_t, n, nullb->dev->blocksize);
+               null_free_sector(nullb, sector);
+               sector += temp >> SECTOR_SHIFT;
+               n -= temp;
+       }
+       spin_unlock_irq(&nullb->lock);
+}
+
 static int null_transfer(struct nullb *nullb, struct page *page,
        unsigned int len, unsigned int off, bool is_write, sector_t sector)
 {
@@ -843,6 +860,11 @@ static int null_handle_rq(struct nullb_cmd *cmd)
 
        sector = blk_rq_pos(rq);
 
+       if (req_op(rq) == REQ_OP_DISCARD) {
+               null_handle_discard(nullb, sector, blk_rq_bytes(rq));
+               return 0;
+       }
+
        spin_lock_irq(&nullb->lock);
        rq_for_each_segment(bvec, rq, iter) {
                len = bvec.bv_len;
@@ -871,6 +893,12 @@ static int null_handle_bio(struct nullb_cmd *cmd)
 
        sector = bio->bi_iter.bi_sector;
 
+       if (bio_op(bio) == REQ_OP_DISCARD) {
+               null_handle_discard(nullb, sector,
+                       bio_sectors(bio) << SECTOR_SHIFT);
+               return 0;
+       }
+
        spin_lock_irq(&nullb->lock);
        bio_for_each_segment(bvec, bio, iter) {
                len = bvec.bv_len;
@@ -1207,6 +1235,16 @@ static void null_del_dev(struct nullb *nullb)
        dev->nullb = NULL;
 }
 
+static void null_config_discard(struct nullb *nullb)
+{
+       if (nullb->dev->discard == false)
+               return;
+       nullb->q->limits.discard_granularity = nullb->dev->blocksize;
+       nullb->q->limits.discard_alignment = nullb->dev->blocksize;
+       blk_queue_max_discard_sectors(nullb->q, UINT_MAX >> 9);
+       queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, nullb->q);
+}
+
 static int null_open(struct block_device *bdev, fmode_t mode)
 {
        return 0;
@@ -1448,6 +1486,8 @@ static int null_add_dev(struct nullb_device *dev)
        blk_queue_logical_block_size(nullb->q, dev->blocksize);
        blk_queue_physical_block_size(nullb->q, dev->blocksize);
 
+       null_config_discard(nullb);
+
        sprintf(nullb->disk_name, "nullb%d", nullb->index);
 
        if (dev->use_lightnvm)
-- 
2.9.5