[Qemu-devel] [PATCH v2 11/15] nbd: add support for NBD_CMD_FLAG_FUA

[Paolo Bonzini]

The server can use it to issue a flush automatically after a
write.  The client can also use it to mimic a write-through
cache.

Signed-off-by: Paolo Bonzini <address@hidden>
---
 block/nbd.c |    8 ++++++++
 nbd.c       |   13 +++++++++++--
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/block/nbd.c b/block/nbd.c
index b6b2f2d..23f83d4 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -216,6 +216,10 @@ static int nbd_write(BlockDriverState *bs, int64_t 
sector_num,
     struct nbd_reply reply;
 
     request.type = NBD_CMD_WRITE;
+    if (!bdrv_enable_write_cache(bs) && (s->nbdflags & NBD_FLAG_SEND_FUA)) {
+        request.type |= NBD_CMD_FLAG_FUA;
+    }
+
     request.handle = (uint64_t)(intptr_t)bs;
     request.from = sector_num * 512;;
     request.len = nb_sectors * 512;
@@ -249,6 +253,10 @@ static int nbd_flush(BlockDriverState *bs)
     }
 
     request.type = NBD_CMD_FLUSH;
+    if (s->nbdflags & NBD_FLAG_SEND_FUA) {
+        request.type |= NBD_CMD_FLAG_FUA;
+    }
+
     request.handle = (uint64_t)(intptr_t)bs;
     request.from = 0;
     request.len = 0;
diff --git a/nbd.c b/nbd.c
index 8852ded..7faa08b 100644
--- a/nbd.c
+++ b/nbd.c
@@ -195,7 +195,8 @@ int nbd_negotiate(int csock, off_t size, uint32_t flags)
     cpu_to_be64w((uint64_t*)(buf + 8), 0x00420281861253LL);
     cpu_to_be64w((uint64_t*)(buf + 16), size);
     cpu_to_be32w((uint32_t*)(buf + 24),
-                 flags | NBD_FLAG_HAS_FLAGS | NBD_FLAG_SEND_FLUSH);
+                 flags | NBD_FLAG_HAS_FLAGS |
+                 NBD_FLAG_SEND_FLUSH | NBD_FLAG_SEND_FUA);
     memset(buf + 28, 0, 124);
 
     if (write_sync(csock, buf, sizeof(buf)) != sizeof(buf)) {
@@ -616,7 +617,7 @@ int nbd_trip(BlockDriverState *bs, int csock, off_t size, 
uint64_t dev_offset,
     reply.handle = request.handle;
     reply.error = 0;
 
-    switch (request.type) {
+    switch (request.type & NBD_CMD_MASK_COMMAND) {
     case NBD_CMD_READ:
         TRACE("Request type is READ");
 
@@ -678,6 +679,14 @@ int nbd_trip(BlockDriverState *bs, int csock, off_t size, 
uint64_t dev_offset,
             }
 
             *offset += request.len;
+
+            if (request.type & NBD_CMD_FLAG_FUA) {
+                ret = bdrv_flush(bs);
+                if (ret < 0) {
+                    LOG("flush failed");
+                    reply.error = -ret;
+                }
+            }
         }
 
         if (nbd_send_reply(csock, &reply) == -1)
-- 
1.7.6