On Thu, Sep 1, 2011 at 11:25 PM, Konrad Rzeszutek Wilk
<konrad.wilk@xxxxxxxxxx> wrote:
> On Thu, Sep 01, 2011 at 06:39:09PM +0800, Li Dongyang wrote:
>> The blkfront driver now will read discard related nodes from xenstore,
>> and set up the request queue, then we can forward the
>> discard requests to backend driver.
>
>
> A better description is as follow:
>
> xen-blkfront: Handle discard requests.
>
> If the backend advertises 'feature-discard', then interrogate
> the backend for alignment, granularity, and max discard block size.
> Setup the request queue with the appropiate values and send the
> discard operation as required.
>
thanks for the description, way better than mine :-)
>
>>
>> Signed-off-by: Li Dongyang <lidongyang@xxxxxxxxxx>
>> ---
>> drivers/block/xen-blkfront.c | 111
>> +++++++++++++++++++++++++++++++++---------
>> 1 files changed, 88 insertions(+), 23 deletions(-)
>>
>> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
>> index 9ea8c25..86e2c63 100644
>> --- a/drivers/block/xen-blkfront.c
>> +++ b/drivers/block/xen-blkfront.c
>> @@ -98,6 +98,9 @@ struct blkfront_info
>> unsigned long shadow_free;
>> unsigned int feature_flush;
>> unsigned int flush_op;
>> + unsigned int feature_discard;
>> + unsigned int discard_granularity;
>> + unsigned int discard_alignment;
>> int is_ready;
>> };
>>
>> @@ -302,29 +305,36 @@ static int blkif_queue_request(struct request *req)
>> ring_req->operation = info->flush_op;
>> }
>>
>> - ring_req->nr_segments = blk_rq_map_sg(req->q, req, info->sg);
>> - BUG_ON(ring_req->nr_segments > BLKIF_MAX_SEGMENTS_PER_REQUEST);
>> + if (unlikely(req->cmd_flags & REQ_DISCARD)) {
>> + /* id, sector_number and handle are set above. */
>> + ring_req->operation = BLKIF_OP_DISCARD;
>> + ring_req->nr_segments = 0;
>> + ring_req->u.discard.nr_sectors = blk_rq_sectors(req);
>> + } else {
>> + ring_req->nr_segments = blk_rq_map_sg(req->q, req, info->sg);
>> + BUG_ON(ring_req->nr_segments > BLKIF_MAX_SEGMENTS_PER_REQUEST);
>>
>> - for_each_sg(info->sg, sg, ring_req->nr_segments, i) {
>> - buffer_mfn = pfn_to_mfn(page_to_pfn(sg_page(sg)));
>> - fsect = sg->offset >> 9;
>> - lsect = fsect + (sg->length >> 9) - 1;
>> - /* install a grant reference. */
>> - ref = gnttab_claim_grant_reference(&gref_head);
>> - BUG_ON(ref == -ENOSPC);
>> + for_each_sg(info->sg, sg, ring_req->nr_segments, i) {
>> + buffer_mfn = pfn_to_mfn(page_to_pfn(sg_page(sg)));
>> + fsect = sg->offset >> 9;
>> + lsect = fsect + (sg->length >> 9) - 1;
>> + /* install a grant reference. */
>> + ref = gnttab_claim_grant_reference(&gref_head);
>> + BUG_ON(ref == -ENOSPC);
>>
>> - gnttab_grant_foreign_access_ref(
>> - ref,
>> - info->xbdev->otherend_id,
>> - buffer_mfn,
>> - rq_data_dir(req) );
>> -
>> - info->shadow[id].frame[i] = mfn_to_pfn(buffer_mfn);
>> - ring_req->u.rw.seg[i] =
>> - (struct blkif_request_segment) {
>> - .gref = ref,
>> - .first_sect = fsect,
>> - .last_sect = lsect };
>> + gnttab_grant_foreign_access_ref(
>> + ref,
>> + info->xbdev->otherend_id,
>> + buffer_mfn,
>> + rq_data_dir(req));
>> +
>> + info->shadow[id].frame[i] = mfn_to_pfn(buffer_mfn);
>> + ring_req->u.rw.seg[i] =
>> + (struct blkif_request_segment) {
>> + .gref = ref,
>> + .first_sect = fsect,
>> + .last_sect = lsect };
>> + }
>> }
>>
>> info->ring.req_prod_pvt++;
>> @@ -399,6 +409,7 @@ wait:
>> static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size)
>> {
>> struct request_queue *rq;
>> + struct blkfront_info *info = gd->private_data;
>>
>> rq = blk_init_queue(do_blkif_request, &blkif_io_lock);
>> if (rq == NULL)
>> @@ -406,6 +417,13 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16
>> sector_size)
>>
>> queue_flag_set_unlocked(QUEUE_FLAG_VIRT, rq);
>>
>> + if (info->feature_discard) {
>> + queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, rq);
>> + blk_queue_max_discard_sectors(rq, get_capacity(gd));
>
> This is not correct. I took a look at the SCSI support for this
> ('sd_config_discard') and if you look there carefully you will see that
> the value can be 64KB for example.
well I don't think so, max_discard_sectors are used to split the bio,
make them not to
exceed the max_discard_sectors, see blkdev_issue_discard, and
that's fine if we use the capacity as max_discard_sectors
in guest: for file backend, there's no need for max_discard_sectors,
and for phy backend, we'll make the blkfront sent out a single big
discard request,
and when we deal with that in blkback by calling blkdev_issue_discard,
the real max_discard_sectors
from phy dev will be used, and take care of splitting bios, Thanks
>
> You need to provide a mechanism similar to 'discard-*' to fetch that data
> from the backend.
>
>> + rq->limits.discard_granularity = info->discard_granularity;
>> + rq->limits.discard_alignment = info->discard_alignment;
>> + }
>> +
>> /* Hard sector size and max sectors impersonate the equiv. hardware. */
>> blk_queue_logical_block_size(rq, sector_size);
>> blk_queue_max_hw_sectors(rq, 512);
>> @@ -722,6 +740,19 @@ static irqreturn_t blkif_interrupt(int irq, void
>> *dev_id)
>>
>> error = (bret->status == BLKIF_RSP_OKAY) ? 0 : -EIO;
>> switch (bret->operation) {
>> + case BLKIF_OP_DISCARD:
>> + if (unlikely(bret->status == BLKIF_RSP_EOPNOTSUPP)) {
>> + struct request_queue *rq = info->rq;
>> + printk(KERN_WARNING "blkfront: %s: discard op
>> failed\n",
>> + info->gd->disk_name);
>> + error = -EOPNOTSUPP;
>> + info->feature_discard = 0;
>> + spin_lock(rq->queue_lock);
>> + queue_flag_clear(QUEUE_FLAG_DISCARD, rq);
>> + spin_unlock(rq->queue_lock);
>> + }
>> + __blk_end_request_all(req, error);
>> + break;
>> case BLKIF_OP_FLUSH_DISKCACHE:
>> case BLKIF_OP_WRITE_BARRIER:
>> if (unlikely(bret->status == BLKIF_RSP_EOPNOTSUPP)) {
>> @@ -1098,6 +1129,33 @@ blkfront_closing(struct blkfront_info *info)
>> bdput(bdev);
>> }
>>
>> +static void blkfront_setup_discard(struct blkfront_info *info)
>> +{
>> + int err;
>> + char *type;
>> + unsigned int discard_granularity;
>> + unsigned int discard_alignment;
>> +
>> + type = xenbus_read(XBT_NIL, info->xbdev->otherend, "type", NULL);
>> + if (IS_ERR(type))
>> + return;
>> +
>> + if (strncmp(type, "phy", 3) == 0) {
>> + err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
>> + "discard-granularity", "%u", &discard_granularity,
>> + "discard-alignment", "%u", &discard_alignment,
>> + NULL);
>> + if (!err) {
>> + info->feature_discard = 1;
>> + info->discard_granularity = discard_granularity;
>> + info->discard_alignment = discard_alignment;
>> + }
>> + } else if (strncmp(type, "file", 4) == 0)
>> + info->feature_discard = 1;
>> +
>> + kfree(type);
>> +}
>> +
>> /*
>> * Invoked when the backend is finally 'ready' (and has told produced
>> * the details about the physical device - #sectors, size, etc).
>> @@ -1108,7 +1166,7 @@ static void blkfront_connect(struct blkfront_info
>> *info)
>> unsigned long sector_size;
>> unsigned int binfo;
>> int err;
>> - int barrier, flush;
>> + int barrier, flush, discard;
>>
>> switch (info->connected) {
>> case BLKIF_STATE_CONNECTED:
>> @@ -1178,7 +1236,14 @@ static void blkfront_connect(struct blkfront_info
>> *info)
>> info->feature_flush = REQ_FLUSH;
>> info->flush_op = BLKIF_OP_FLUSH_DISKCACHE;
>> }
>> -
>> +
>> + err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
>> + "feature-discard", "%d", &discard,
>> + NULL);
>> +
>> + if (!err && discard)
>> + blkfront_setup_discard(info);
>> +
>> err = xlvbd_alloc_gendisk(sectors, info, binfo, sector_size);
>> if (err) {
>> xenbus_dev_fatal(info->xbdev, err, "xlvbd_add at %s",
>> --
>> 1.7.6
>
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