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block: don't allocate a payload for discard request

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Allocating a fixed payload for discard requests always was a horrible hack,
and it's not coming to byte us when adding support for discard in DM/MD.

So change the code to leave the allocation of a payload to the lowlevel
driver.  Unfortunately that means we'll need another hack, which allows
us to update the various block layer length fields indicating that we
have a payload.  Instead of hiding this in sd.c, which we already partially
do for UNMAP support add a documented helper in the core block layer for it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
This commit is contained in:
Christoph Hellwig
2010-06-18 16:59:42 +02:00
committed by Jens Axboe
parent 082439004b
commit 66ac028019
4 changed files with 75 additions and 46 deletions
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54
drivers/scsi/sd.c
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@@ -411,22 +411,25 @@ static void sd_prot_op(struct scsi_cmnd *scmd, unsigned int dif)
}
/**
* sd_prepare_discard - unmap blocks on thinly provisioned device
* scsi_setup_discard_cmnd - unmap blocks on thinly provisioned device
* @sdp: scsi device to operate one
* @rq: Request to prepare
*
* Will issue either UNMAP or WRITE SAME(16) depending on preference
* indicated by target device.
**/
static int sd_prepare_discard(struct request *rq)
static int scsi_setup_discard_cmnd(struct scsi_device *sdp, struct request *rq)
{
struct scsi_disk *sdkp = scsi_disk(rq->rq_disk);
struct bio *bio = rq->bio;
sector_t sector = bio->bi_sector;
unsigned int num = bio_sectors(bio);
unsigned int nr_sectors = bio_sectors(bio);
unsigned int len;
struct page *page;
if (sdkp->device->sector_size == 4096) {
sector >>= 3;
num >>= 3;
nr_sectors >>= 3;
}
rq->cmd_type = REQ_TYPE_BLOCK_PC;
@@ -434,31 +437,35 @@ static int sd_prepare_discard(struct request *rq)
memset(rq->cmd, 0, rq->cmd_len);
if (sdkp->unmap) {
char *buf = kmap_atomic(bio_page(bio), KM_USER0);
page = alloc_page(GFP_ATOMIC | __GFP_ZERO);
if (!page)
return BLKPREP_DEFER;
if (sdkp->unmap) {
char *buf = page_address(page);
rq->cmd_len = 10;
rq->cmd[0] = UNMAP;
rq->cmd[8] = 24;
rq->cmd_len = 10;
/* Ensure that data length matches payload */
rq->__data_len = bio->bi_size = bio->bi_io_vec->bv_len = 24;
put_unaligned_be16(6 + 16, &buf[0]);
put_unaligned_be16(16, &buf[2]);
put_unaligned_be64(sector, &buf[8]);
put_unaligned_be32(num, &buf[16]);
put_unaligned_be32(nr_sectors, &buf[16]);
kunmap_atomic(buf, KM_USER0);
len = 24;
} else {
rq->cmd_len = 16;
rq->cmd[0] = WRITE_SAME_16;
rq->cmd[1] = 0x8; /* UNMAP */
put_unaligned_be64(sector, &rq->cmd[2]);
put_unaligned_be32(num, &rq->cmd[10]);
rq->cmd_len = 16;
put_unaligned_be32(nr_sectors, &rq->cmd[10]);
len = sdkp->device->sector_size;
}
return BLKPREP_OK;
blk_add_request_payload(rq, page, len);
return scsi_setup_blk_pc_cmnd(sdp, rq);
}
/**
@@ -485,10 +492,10 @@ static int sd_prep_fn(struct request_queue *q, struct request *rq)
* Discard request come in as REQ_TYPE_FS but we turn them into
* block PC requests to make life easier.
*/
if (rq->cmd_flags & REQ_DISCARD)
ret = sd_prepare_discard(rq);
if (rq->cmd_type == REQ_TYPE_BLOCK_PC) {
if (rq->cmd_flags & REQ_DISCARD) {
ret = scsi_setup_discard_cmnd(sdp, rq);
goto out;
} else if (rq->cmd_type == REQ_TYPE_BLOCK_PC) {
ret = scsi_setup_blk_pc_cmnd(sdp, rq);
goto out;
} else if (rq->cmd_type != REQ_TYPE_FS) {
@@ -1163,6 +1170,15 @@ static int sd_done(struct scsi_cmnd *SCpnt)
int sense_valid = 0;
int sense_deferred = 0;
/*
* If this is a discard request that originated from the kernel
* we need to free our payload here. Note that we need to check
* the request flag as the normal payload rules apply for
* pass-through UNMAP / WRITE SAME requests.
*/
if (SCpnt->request->cmd_flags & REQ_DISCARD)
__free_page(bio_page(SCpnt->request->bio));
if (result) {
sense_valid = scsi_command_normalize_sense(SCpnt, &sshdr);
if (sense_valid)