On Thu, 30 Jan 2014, Olaf Hering wrote:
> Implement discard support for xen_disk. It makes use of the existing
> discard code in qemu.
>
> The discard support is enabled unconditionally. The tool stack may provide a
> property "discard-enable" in the backend node to optionally disable discard
> support. This is helpful in case the backing file was intentionally created
> non-sparse to avoid fragmentation.
>
> Signed-off-by: Olaf Hering <o...@aepfle.de>
> ---
>
> The counter part for libxl is here, will go into xen-4.5:
> http://lists.xenproject.org/archives/html/xen-devel/2014-01/msg02632.html
>
>
> checkpatch comaplains about tabs in hw/block/xen_blkif.h.
> The whole file is full of tabs, like the whole source tree...
>
> If desired I will send a follow up patch to wipe tabs in hw/block/xen_blkif.h
No worries. I'll add this patch to my queue.
>
> hw/block/xen_blkif.h | 12 ++++++++++++
> hw/block/xen_disk.c | 34 ++++++++++++++++++++++++++++++++++
> 2 files changed, 46 insertions(+)
>
> diff --git a/hw/block/xen_blkif.h b/hw/block/xen_blkif.h
> index c0f4136..711b692 100644
> --- a/hw/block/xen_blkif.h
> +++ b/hw/block/xen_blkif.h
> @@ -79,6 +79,12 @@ static inline void blkif_get_x86_32_req(blkif_request_t
> *dst, blkif_x86_32_reque
> dst->handle = src->handle;
> dst->id = src->id;
> dst->sector_number = src->sector_number;
> + if (src->operation == BLKIF_OP_DISCARD) {
> + struct blkif_request_discard *s = (void *)src;
> + struct blkif_request_discard *d = (void *)dst;
> + d->nr_sectors = s->nr_sectors;
> + return;
> + }
> if (n > src->nr_segments)
> n = src->nr_segments;
> for (i = 0; i < n; i++)
> @@ -94,6 +100,12 @@ static inline void blkif_get_x86_64_req(blkif_request_t
> *dst, blkif_x86_64_reque
> dst->handle = src->handle;
> dst->id = src->id;
> dst->sector_number = src->sector_number;
> + if (src->operation == BLKIF_OP_DISCARD) {
> + struct blkif_request_discard *s = (void *)src;
> + struct blkif_request_discard *d = (void *)dst;
> + d->nr_sectors = s->nr_sectors;
> + return;
> + }
> if (n > src->nr_segments)
> n = src->nr_segments;
> for (i = 0; i < n; i++)
> diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
> index 098f6c6..e74efc7 100644
> --- a/hw/block/xen_disk.c
> +++ b/hw/block/xen_disk.c
> @@ -114,6 +114,7 @@ struct XenBlkDev {
> int requests_finished;
>
> /* Persistent grants extension */
> + gboolean feature_discard;
> gboolean feature_persistent;
> GTree *persistent_gnts;
> unsigned int persistent_gnt_count;
> @@ -253,6 +254,8 @@ static int ioreq_parse(struct ioreq *ioreq)
> case BLKIF_OP_WRITE:
> ioreq->prot = PROT_READ; /* from memory */
> break;
> + case BLKIF_OP_DISCARD:
> + return 0;
> default:
> xen_be_printf(&blkdev->xendev, 0, "error: unknown operation (%d)\n",
> ioreq->req.operation);
> @@ -521,6 +524,17 @@ static int ioreq_runio_qemu_aio(struct ioreq *ioreq)
> &ioreq->v, ioreq->v.size / BLOCK_SIZE,
> qemu_aio_complete, ioreq);
> break;
> + case BLKIF_OP_DISCARD:
> + {
> + struct blkif_request_discard *discard_req = (void *)&ioreq->req;
> + bdrv_acct_start(blkdev->bs, &ioreq->acct,
> + discard_req->nr_sectors * BLOCK_SIZE,
> BDRV_ACCT_WRITE);
> + ioreq->aio_inflight++;
> + bdrv_aio_discard(blkdev->bs,
> + discard_req->sector_number, discard_req->nr_sectors,
> + qemu_aio_complete, ioreq);
> + break;
> + }
> default:
> /* unknown operation (shouldn't happen -- parse catches this) */
> goto err;
> @@ -699,6 +713,21 @@ static void blk_alloc(struct XenDevice *xendev)
> }
> }
>
> +static void blk_parse_discard(struct XenBlkDev *blkdev)
> +{
> + int enable;
> +
> + blkdev->feature_discard = true;
> +
> + if (xenstore_read_be_int(&blkdev->xendev, "discard-enable", &enable) ==
> 0) {
> + blkdev->feature_discard = !!enable;
> + }
> +
> + if (blkdev->feature_discard) {
> + xenstore_write_be_int(&blkdev->xendev, "feature-discard", 1);
> + }
> +}
> +
> static int blk_init(struct XenDevice *xendev)
> {
> struct XenBlkDev *blkdev = container_of(xendev, struct XenBlkDev,
> xendev);
> @@ -766,6 +795,8 @@ static int blk_init(struct XenDevice *xendev)
> xenstore_write_be_int(&blkdev->xendev, "feature-persistent", 1);
> xenstore_write_be_int(&blkdev->xendev, "info", info);
>
> + blk_parse_discard(blkdev);
> +
> g_free(directiosafe);
> return 0;
>
> @@ -801,6 +832,9 @@ static int blk_connect(struct XenDevice *xendev)
> qflags |= BDRV_O_RDWR;
> readonly = false;
> }
> + if (blkdev->feature_discard) {
> + qflags |= BDRV_O_UNMAP;
> + }
>
> /* init qemu block driver */
> index = (blkdev->xendev.dev - 202 * 256) / 16;
>
