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block: use normal I/O path for discard requests

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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>
This commit is contained in:
Christoph Hellwig
2009-09-30 13:52:12 +02:00
committed by Jens Axboe
parent 3bd0f0c763
commit 1122a26f2a
6 changed files with 39 additions and 43 deletions
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19
drivers/mtd/mtd_blkdevs.c
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@ -32,14 +32,6 @@ struct mtd_blkcore_priv {
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 @@ static int do_blktrans_request(struct mtd_blktrans_ops *tr,
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 @@ static int do_blktrans_request(struct mtd_blktrans_ops *tr,
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 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
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;