block: use normal I/O path for discard requests
prepare_discard_fn() was being called in a place where memory allocation
was effectively impossible. This makes it inappropriate for all but
the most trivial translations of Linux's DISCARD operation to the block
command set. Additionally adding a payload there makes the ownership
of the bio backing unclear as it's now allocated by the device driver
and not the submitter as usual.
It is replaced with QUEUE_FLAG_DISCARD which is used to indicate whether
the queue supports discard operations or not. blkdev_issue_discard now
allocates a one-page, sector-length payload which is the right thing
for the common ATA and SCSI implementations.
The mtd implementation of prepare_discard_fn() is replaced with simply
checking for the request being a discard.
Largely based on a previous patch from Matthew Wilcox <matthew@wil.cx>
which did the prepare_discard_fn but not the different payload allocation
yet.
Signed-off-by: Christoph Hellwig <hch@lst.de>
diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
index 0acbf4f..8ca17a3 100644
--- a/drivers/mtd/mtd_blkdevs.c
+++ b/drivers/mtd/mtd_blkdevs.c
@@ -32,14 +32,6 @@
spinlock_t queue_lock;
};
-static int blktrans_discard_request(struct request_queue *q,
- struct request *req)
-{
- req->cmd_type = REQ_TYPE_LINUX_BLOCK;
- req->cmd[0] = REQ_LB_OP_DISCARD;
- return 0;
-}
-
static int do_blktrans_request(struct mtd_blktrans_ops *tr,
struct mtd_blktrans_dev *dev,
struct request *req)
@@ -52,10 +44,6 @@
buf = req->buffer;
- if (req->cmd_type == REQ_TYPE_LINUX_BLOCK &&
- req->cmd[0] == REQ_LB_OP_DISCARD)
- return tr->discard(dev, block, nsect);
-
if (!blk_fs_request(req))
return -EIO;
@@ -63,6 +51,9 @@
get_capacity(req->rq_disk))
return -EIO;
+ if (blk_discard_rq(req))
+ return tr->discard(dev, block, nsect);
+
switch(rq_data_dir(req)) {
case READ:
for (; nsect > 0; nsect--, block++, buf += tr->blksize)
@@ -380,8 +371,8 @@
tr->blkcore_priv->rq->queuedata = tr;
blk_queue_logical_block_size(tr->blkcore_priv->rq, tr->blksize);
if (tr->discard)
- blk_queue_set_discard(tr->blkcore_priv->rq,
- blktrans_discard_request);
+ queue_flag_set_unlocked(QUEUE_FLAG_DISCARD,
+ tr->blkcore_priv->rq);
tr->blkshift = ffs(tr->blksize) - 1;