References: FATE#316071
Subject: qemu-upstream: add discard support for xen_disk
Git-commit: f31352041bdde436c3f6d07e1525a42e48dec215

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.

v2:
rename xenstore property from discard_enable to discard-enable
move discard_req to case BLKIF_OP_DISCARD

Signed-off-by: Olaf Hering <olaf@aepfle.de>
---
 tools/qemu-xen-dir-remote/hw/block/xen_blkif.h |   12 ++++++++++
 tools/qemu-xen-dir-remote/hw/block/xen_disk.c  |   30 +++++++++++++++++++++++++
 2 files changed, 42 insertions(+)

Index: xen-4.4.3-testing/tools/qemu-xen-dir-remote/hw/block/xen_blkif.h
===================================================================
--- xen-4.4.3-testing.orig/tools/qemu-xen-dir-remote/hw/block/xen_blkif.h
+++ xen-4.4.3-testing/tools/qemu-xen-dir-remote/hw/block/xen_blkif.h
@@ -79,6 +79,12 @@ static inline void blkif_get_x86_32_req(
 	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;
+	}
 	/* prevent the compiler from optimizing the code and using src->nr_segments instead */
 	barrier();
 	if (n > dst->nr_segments)
@@ -96,6 +102,12 @@ static inline void blkif_get_x86_64_req(
 	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;
+	}
 	/* prevent the compiler from optimizing the code and using src->nr_segments instead */
 	barrier();
 	if (n > dst->nr_segments)
Index: xen-4.4.3-testing/tools/qemu-xen-dir-remote/hw/block/xen_disk.c
===================================================================
--- xen-4.4.3-testing.orig/tools/qemu-xen-dir-remote/hw/block/xen_disk.c
+++ xen-4.4.3-testing/tools/qemu-xen-dir-remote/hw/block/xen_disk.c
@@ -121,6 +121,7 @@ struct XenBlkDev {
     int                 requests_finished;
 
     /* Persistent grants extension */
+    gboolean            feature_discard;
     gboolean            feature_persistent;
     GTree               *persistent_gnts;
     GSList              *persistent_regions;
@@ -278,6 +279,8 @@ static int ioreq_parse(struct ioreq *ior
     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);
@@ -563,6 +566,16 @@ static int ioreq_runio_qemu_aio(struct i
                         &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;
@@ -741,6 +754,19 @@ static void blk_alloc(struct XenDevice *
     }
 }
 
+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);
@@ -808,6 +834,8 @@ static int blk_init(struct XenDevice *xe
     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;
 
@@ -843,6 +871,8 @@ static int blk_connect(struct XenDevice
         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;
