The NBD spec was recently clarified to state that clients should
not send 0-length requests to the server, as the server behavior
is undefined [1]. We know that qemu-nbd's behavior is a successful
no-op (once it has filtered for read-only exports), but other NBD
implementations might return an error. To avoid any questionable
server implementations, it is better to just short-circuit such
requests on the client side (we are relying on the block layer to
already filter out requests such as invalid offset, write to a
read-only volume, and so forth).
[1] https://github.com/NetworkBlockDevice/nbd/commit/ee926037
Signed-off-by: Eric Blake <address@hidden>
---
block/nbd-client.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/block/nbd-client.c b/block/nbd-client.c
index daa4392531..0a675d0fab 100644
--- a/block/nbd-client.c
+++ b/block/nbd-client.c
@@ -674,6 +674,9 @@ int nbd_client_co_preadv(BlockDriverState *bs, uint64_t
offset,
assert(bytes <= NBD_MAX_BUFFER_SIZE);
assert(!flags);
+ if (!bytes) {
+ return 0;
+ }
ret = nbd_co_send_request(bs, &request, NULL);
if (ret < 0) {
return ret;
@@ -705,6 +708,9 @@ int nbd_client_co_pwritev(BlockDriverState *bs, uint64_t
offset,
assert(bytes <= NBD_MAX_BUFFER_SIZE);
+ if (!bytes) {
+ return 0;
+ }
return nbd_co_request(bs, &request, qiov);
}
@@ -731,6 +737,9 @@ int nbd_client_co_pwrite_zeroes(BlockDriverState *bs,
int64_t offset,
request.flags |= NBD_CMD_FLAG_NO_HOLE;
}
+ if (!bytes) {
+ return 0;
+ }
return nbd_co_request(bs, &request, NULL);
}
@@ -759,7 +768,7 @@ int nbd_client_co_pdiscard(BlockDriverState *bs, int64_t
offset, int bytes)
};
assert(!(client->info.flags & NBD_FLAG_READ_ONLY));
- if (!(client->info.flags & NBD_FLAG_SEND_TRIM)) {
+ if (!(client->info.flags & NBD_FLAG_SEND_TRIM) || !bytes) {
return 0;
}