[Qemu-devel] [PATCH] nbd: Implement NBD_CMD_HAS_ZERO_INIT

[Yi Fang]

NBD client has not implemented callback for .bdrv_has_zero_init. So
bdrv_has_zero_init always returns 0 when doing non-shared storage
migration.
This patch implemented NBD_CMD_HAS_ZERO_INIT and will avoid unnecessary
set-dirty.

Signed-off-by: Yi Fang <address@hidden>
---
 block/block-backend.c          |  5 +++++
 block/nbd-client.c             | 28 ++++++++++++++++++++++++++++
 block/nbd-client.h             |  1 +
 block/nbd.c                    |  8 ++++++++
 include/block/nbd.h            |  3 +++
 include/sysemu/block-backend.h |  1 +
 nbd/server.c                   | 10 +++++++++-
 7 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/block/block-backend.c b/block/block-backend.c
index efbf398..4369c85 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -1239,6 +1239,11 @@ void blk_drain_all(void)
     bdrv_drain_all();
 }
 
+int blk_has_zero_init(BlockBackend *blk)
+{
+        return bdrv_has_zero_init(blk_bs(blk));
+}
+
 void blk_set_on_error(BlockBackend *blk, BlockdevOnError on_read_error,
                       BlockdevOnError on_write_error)
 {
diff --git a/block/nbd-client.c b/block/nbd-client.c
index 3779c6c..8b1d98d 100644
--- a/block/nbd-client.c
+++ b/block/nbd-client.c
@@ -376,6 +376,34 @@ void nbd_client_attach_aio_context(BlockDriverState *bs,
                        false, nbd_reply_ready, NULL, bs);
 }
 
+int nbd_client_co_has_zero_init(BlockDriverState *bs)
+{
+    NBDClientSession *client = nbd_get_client_session(bs);
+    NBDRequest request = { .type = NBD_CMD_HAS_ZERO_INIT };
+    NBDReply reply;
+    ssize_t ret;
+
+    if (!(client->nbdflags & NBD_FLAG_HAS_ZERO_INIT)) {
+        return 0;
+    }
+
+    request.from = 0;
+    request.len = 0;
+
+    nbd_coroutine_start(client, &request);
+    ret = nbd_co_send_request(bs, &request, NULL);
+    if (ret < 0) {
+        reply.error = -ret;
+    } else {
+        nbd_co_receive_reply(client, &request, &reply, NULL);
+    }
+    nbd_coroutine_end(client, &request);
+    if (reply.error == 0) {
+        return 1;
+    }
+    return 0;
+}
+
 void nbd_client_close(BlockDriverState *bs)
 {
     NBDClientSession *client = nbd_get_client_session(bs);
diff --git a/block/nbd-client.h b/block/nbd-client.h
index f8d6006..ec01938 100644
--- a/block/nbd-client.h
+++ b/block/nbd-client.h
@@ -56,5 +56,6 @@ int nbd_client_co_preadv(BlockDriverState *bs, uint64_t 
offset,
 void nbd_client_detach_aio_context(BlockDriverState *bs);
 void nbd_client_attach_aio_context(BlockDriverState *bs,
                                    AioContext *new_context);
+int nbd_client_co_has_zero_init(BlockDriverState *bs);
 
 #endif /* NBD_CLIENT_H */
diff --git a/block/nbd.c b/block/nbd.c
index 35f24be..40dd9a2 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -552,6 +552,11 @@ static void nbd_refresh_filename(BlockDriverState *bs, 
QDict *options)
     bs->full_open_options = opts;
 }
 
+static int nbd_co_has_zero_init(BlockDriverState *bs)
+{
+    return nbd_client_co_has_zero_init(bs);
+}
+
 static BlockDriver bdrv_nbd = {
     .format_name                = "nbd",
     .protocol_name              = "nbd",
@@ -569,6 +574,7 @@ static BlockDriver bdrv_nbd = {
     .bdrv_detach_aio_context    = nbd_detach_aio_context,
     .bdrv_attach_aio_context    = nbd_attach_aio_context,
     .bdrv_refresh_filename      = nbd_refresh_filename,
+    .bdrv_has_zero_init         = nbd_co_has_zero_init,
 };
 
 static BlockDriver bdrv_nbd_tcp = {
@@ -588,6 +594,7 @@ static BlockDriver bdrv_nbd_tcp = {
     .bdrv_detach_aio_context    = nbd_detach_aio_context,
     .bdrv_attach_aio_context    = nbd_attach_aio_context,
     .bdrv_refresh_filename      = nbd_refresh_filename,
+    .bdrv_has_zero_init         = nbd_co_has_zero_init,
 };
 
 static BlockDriver bdrv_nbd_unix = {
@@ -607,6 +614,7 @@ static BlockDriver bdrv_nbd_unix = {
     .bdrv_detach_aio_context    = nbd_detach_aio_context,
     .bdrv_attach_aio_context    = nbd_attach_aio_context,
     .bdrv_refresh_filename      = nbd_refresh_filename,
+    .bdrv_has_zero_init         = nbd_co_has_zero_init,
 };
 
 static void bdrv_nbd_init(void)
diff --git a/include/block/nbd.h b/include/block/nbd.h
index 3e373f0..9aa9265 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -72,6 +72,7 @@ typedef struct NBDReply NBDReply;
 #define NBD_FLAG_ROTATIONAL     (1 << 4)        /* Use elevator algorithm - 
rotational media */
 #define NBD_FLAG_SEND_TRIM      (1 << 5)        /* Send TRIM (discard) */
 #define NBD_FLAG_SEND_WRITE_ZEROES (1 << 6)     /* Send WRITE_ZEROES */
+#define NBD_FLAG_HAS_ZERO_INIT  (1 << 8)        /* Send HAS_ZERO_INIT */
 
 /* New-style handshake (global) flags, sent from server to client, and
    control what will happen during handshake phase. */
@@ -109,6 +110,8 @@ enum {
     NBD_CMD_TRIM = 4,
     /* 5 reserved for failed experiment NBD_CMD_CACHE */
     NBD_CMD_WRITE_ZEROES = 6,
+    /* 7 reserved for STRUCTURED_REPLY */
+    NBD_CMD_HAS_ZERO_INIT = 8,
 };
 
 #define NBD_DEFAULT_PORT       10809
diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
index 6444e41..9bd0822 100644
--- a/include/sysemu/block-backend.h
+++ b/include/sysemu/block-backend.h
@@ -156,6 +156,7 @@ int blk_flush(BlockBackend *blk);
 int blk_commit_all(void);
 void blk_drain(BlockBackend *blk);
 void blk_drain_all(void);
+int blk_has_zero_init(BlockBackend *blk);
 void blk_set_on_error(BlockBackend *blk, BlockdevOnError on_read_error,
                       BlockdevOnError on_write_error);
 BlockdevOnError blk_get_on_error(BlockBackend *blk, bool is_read);
diff --git a/nbd/server.c b/nbd/server.c
index 5b76261..7ae91b7 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -617,7 +617,8 @@ static coroutine_fn int nbd_negotiate(NBDClientNewData 
*data)
     int rc;
     const uint16_t myflags = (NBD_FLAG_HAS_FLAGS | NBD_FLAG_SEND_TRIM |
                               NBD_FLAG_SEND_FLUSH | NBD_FLAG_SEND_FUA |
-                              NBD_FLAG_SEND_WRITE_ZEROES);
+                              NBD_FLAG_SEND_WRITE_ZEROES |
+                              NBD_FLAG_HAS_ZERO_INIT);
     bool oldStyle;
     size_t len;
 
@@ -1321,6 +1322,13 @@ static void nbd_trip(void *opaque)
             goto out;
         }
         break;
+    case NBD_CMD_HAS_ZERO_INIT:
+        TRACE("Request type is HAS_ZERO_INIT");
+        reply.error = !blk_has_zero_init(exp->blk);
+        if (nbd_co_send_reply(req, &reply, 0) < 0) {
+            goto out;
+        }
+        break;
     default:
         LOG("invalid request type (%" PRIu32 ") received", request.type);
         reply.error = EINVAL;
-- 
1.8.5