sheepdog: refine discard support

This patch refines discard support of the sheepdog driver. The
existing discard mechanism was implemented on SD_OP_DISCARD_OBJ, which
was introduced before fine grained reference counting on newer
sheepdog. It doesn't care about relations of snapshots and clones and
discards objects unconditionally.

With this patch, the driver just updates an inode object for updating
reference. Removing the object is done in sheep process side.

Cc: Teruaki Ishizaki <ishizaki.teruaki@lab.ntt.co.jp>
Cc: Vasiliy Tolstov <v.tolstov@selfip.ru>
Cc: Jeff Cody <jcody@redhat.com>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
Tested-by: Vasiliy Tolstov <v.tolstov@selfip.ru>
Message-id: 1441076590-8015-3-git-send-email-mitake.hitoshi@lab.ntt.co.jp
Signed-off-by: Jeff Cody <jcody@redhat.com>

block/sheepdog.c

@@ -28,7 +28,6 @@
 #define SD_OP_READ_OBJ       0x02
 #define SD_OP_WRITE_OBJ      0x03
 /* 0x04 is used internally by Sheepdog */
-#define SD_OP_DISCARD_OBJ    0x05
 
 #define SD_OP_NEW_VDI        0x11
 #define SD_OP_LOCK_VDI       0x12
@@ -861,10 +860,6 @@ static void coroutine_fn aio_read_response(void *opaque)
             rsp.result = SD_RES_SUCCESS;
             s->discard_supported = false;
             break;
-        case SD_RES_SUCCESS:
-            idx = data_oid_to_idx(aio_req->oid);
-            s->inode.data_vdi_id[idx] = 0;
-            break;
         default:
             break;
         }
@@ -1179,7 +1174,13 @@ static void coroutine_fn add_aio_request(BDRVSheepdogState *s, AIOReq *aio_req,
         hdr.flags = SD_FLAG_CMD_WRITE | flags;
         break;
     case AIOCB_DISCARD_OBJ:
-        hdr.opcode = SD_OP_DISCARD_OBJ;
+        hdr.opcode = SD_OP_WRITE_OBJ;
+        hdr.flags = SD_FLAG_CMD_WRITE | flags;
+        s->inode.data_vdi_id[data_oid_to_idx(oid)] = 0;
+        offset = offsetof(SheepdogInode,
+                          data_vdi_id[data_oid_to_idx(oid)]);
+        oid = vid_to_vdi_oid(s->inode.vdi_id);
+        wlen = datalen = sizeof(uint32_t);
         break;
     }
 
@@ -2214,7 +2215,9 @@ static int coroutine_fn sd_co_rw_vector(void *p)
         }
 
         aio_req = alloc_aio_req(s, acb, oid, len, offset, flags, create,
-                                old_oid, done);
+                                old_oid,
+                                acb->aiocb_type == AIOCB_DISCARD_OBJ ?
+                                0 : done);
         QLIST_INSERT_HEAD(&s->inflight_aio_head, aio_req, aio_siblings);
 
         add_aio_request(s, aio_req, acb->qiov->iov, acb->qiov->niov,
@@ -2650,15 +2653,23 @@ static coroutine_fn int sd_co_discard(BlockDriverState *bs, int64_t sector_num,
                                       int nb_sectors)
 {
     SheepdogAIOCB *acb;
-    QEMUIOVector dummy;
     BDRVSheepdogState *s = bs->opaque;
     int ret;
+    QEMUIOVector discard_iov;
+    struct iovec iov;
+    uint32_t zero = 0;
 
     if (!s->discard_supported) {
             return 0;
     }
 
-    acb = sd_aio_setup(bs, &dummy, sector_num, nb_sectors);
+    memset(&discard_iov, 0, sizeof(discard_iov));
+    memset(&iov, 0, sizeof(iov));
+    iov.iov_base = &zero;
+    iov.iov_len = sizeof(zero);
+    discard_iov.iov = &iov;
+    discard_iov.niov = 1;
+    acb = sd_aio_setup(bs, &discard_iov, sector_num, nb_sectors);
     acb->aiocb_type = AIOCB_DISCARD_OBJ;
     acb->aio_done_func = sd_finish_aiocb;