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Re: [Qemu-block] [Qemu-devel] [PATCH] block: split large discard request
From: |
Olaf Hering |
Subject: |
Re: [Qemu-block] [Qemu-devel] [PATCH] block: split large discard requests from block frontend |
Date: |
Thu, 17 Nov 2016 17:27:19 +0100 |
User-agent: |
Mutt/1.6.2 (6759) |
On Thu, Nov 17, Olaf Hering wrote:
> Looking at current master, BLKIF_OP_DISCARD is indeed broken. The values
> passed from the guest are u64 and get stashed into signed values. I will
> add a loop to repeatedly call blk_aio_pdiscard with small chunks of
> BDRV_REQUEST_MAX_SECTORS.
I have not compile tested the change below, but thats the way how I
would deal with it:
diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
index 3a7dc19..5962c4b 100644
--- a/hw/block/xen_disk.c
+++ b/hw/block/xen_disk.c
@@ -660,6 +660,38 @@ static void qemu_aio_complete(void *opaque, int ret)
qemu_bh_schedule(ioreq->blkdev->bh);
}
+static bool blk_split_discard(struct ioreq *ioreq, blkif_sector_t
sector_number, uint64_t nr_sectors)
+{
+ struct XenBlkDev *blkdev = ioreq->blkdev;
+ int64_t byte_offset;
+ int bytes;
+ uint64_t byte_limit = INT64_MAX + INT_MAX;
+ uint64_t sec_start = sector_number;
+ uint64_t sec_count = nr_sectors;
+ uint64_t byte_remaining;
+ uint64_t limit = BDRV_REQUEST_MAX_SECTORS << BDRV_SECTOR_BITS;
+
+ /* Wrap around? */
+ if ((sec_start + sec_count) < sec_count)
+ return false;
+ /* Overflowing byte limit? */
+ if ((sec_start + sec_count) > (byte_limit >> BDRV_SECTOR_BITS))
+ return false;
+
+ byte_offset = sec_start << BDRV_SECTOR_BITS;
+ byte_remaining = sec_count << BDRV_SECTOR_BITS;
+ do {
+ bytes = byte_remaining > limit ? limit : byte_remaining;
+ ioreq->aio_inflight++;
+ blk_aio_pdiscard(blkdev->blk, byte_offset, bytes,
+ qemu_aio_complete, ioreq);
+ byte_remaining -= bytes;
+ byte_offset += bytes;
+ } while (byte_remaining > 0);
+
+ return true;
+}
+
static int ioreq_runio_qemu_aio(struct ioreq *ioreq)
{
struct XenBlkDev *blkdev = ioreq->blkdev;
@@ -708,12 +740,9 @@ static int ioreq_runio_qemu_aio(struct ioreq *ioreq)
break;
case BLKIF_OP_DISCARD:
{
- struct blkif_request_discard *discard_req = (void *)&ioreq->req;
- ioreq->aio_inflight++;
- blk_aio_pdiscard(blkdev->blk,
- discard_req->sector_number << BDRV_SECTOR_BITS,
- discard_req->nr_sectors << BDRV_SECTOR_BITS,
- qemu_aio_complete, ioreq);
+ struct blkif_request_discard *req = (void *)&ioreq->req;
+ if (blk_split_discard(ioreq, req->sector_number, req->nr_sectors))
+ goto err;
break;
}
default:
Olaf
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