[PATCH 3/3] nbd: map DISCARD requests to a new nbd request type

Paolo Bonzini
2011-09-07T16:19:39Z

When the feature is enabled, set QUEUE_FLAG_DISCARD and transmit those as
NBD_CMD_TRIM requests.

I used "trim" instead of "discard" to avoid confusion with the existing
NBD_CMD_DISC that is used for disconnect.

Cc: Paul Clements <Paul.Clements@steeleye.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
drivers/block/nbd.c | 15 ++++++++++++---
include/linux/nbd.h | 4 +++-
2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index c4fe9c8..71ebaab 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -98,6 +98,7 @@ static const char *nbdcmd_to_ascii(int cmd)
case NBD_CMD_READ: return "read";
case NBD_CMD_WRITE: return "write";
case NBD_CMD_DISC: return "disconnect";
+ case NBD_CMD_TRIM: return "trim (discard)";
}
return "invalid";
}
@@ -454,9 +455,13 @@ static void nbd_handle_req(struct nbd_device *lo, struct request *req)
if (req->cmd_type != REQ_TYPE_FS)
goto error_out;

- if (rq_data_dir(req) == WRITE)
- nbd_cmd(req) = NBD_CMD_WRITE;
- else
+ if (rq_data_dir(req) == WRITE) {
+ if ((req->cmd_flags & REQ_DISCARD)) {
+ WARN_ON(!(lo->flags & NBD_FEATURE_TRIM));
+ nbd_cmd(req) = NBD_CMD_TRIM;
+ } else
+ nbd_cmd(req) = NBD_CMD_WRITE;
+ } else
nbd_cmd(req) = NBD_CMD_READ;

req->errors = 0;
@@ -659,6 +664,9 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *lo,
return -EINVAL;

mutex_unlock(&lo->tx_lock);
+ if (lo->flags & NBD_FEATURE_TRIM)
+ queue_flag_set_unlocked(QUEUE_FLAG_DISCARD,
+ lo->disk->queue);

thread = kthread_create(nbd_thread, lo, lo->disk->disk_name);
if (IS_ERR(thread)) {
@@ -677,6 +685,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *lo,
lo->file = NULL;
nbd_clear_que(lo);
printk(KERN_WARNING "%s: queue cleared\n", lo->disk->disk_name);
+ queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, lo->disk->queue);
if (file)
fput(file);
lo->flags = 0;
@@ -796,6 +805,9 @@ static int __init nbd_init(void)
* Tell the block layer that we are not a rotational device
*/
queue_flag_set_unlocked(QUEUE_FLAG_NONROT, disk->queue);
+ disk->queue->limits.discard_granularity = 512;
+ disk->queue->limits.max_discard_sectors = UINT_MAX;
+ disk->queue->limits.discard_zeroes_data = 0;
}

if (register_blkdev(NBD_MAJOR, "nbd")) {
diff --git a/include/linux/nbd.h b/include/linux/nbd.h
index 926f19d..7048463 100644
--- a/include/linux/nbd.h
+++ b/include/linux/nbd.h
@@ -33,11 +33,13 @@
* not want any overlap. Bits 32-63 are reserved because they
* are inaccessible on 32-bit platforms. */
#define NBD_FEATURE_RESERVED 0xFFFFFFFF00000003LL
+#define NBD_FEATURE_TRIM (1 << 2)

enum {
NBD_CMD_READ = 0,
NBD_CMD_WRITE = 1,
- NBD_CMD_DISC = 2
+ NBD_CMD_DISC = 2,
+ NBD_CMD_TRIM = 3
};

#define nbd_cmd(req) ((req)->cmd[0])
--
1.7.6