nbd: generalize usage of nbd_read

We generally do very similar things around nbd_read: error_prepend
specifying what we have tried to read, and be_to_cpu conversion of
integers.

So, it seems reasonable to move common things to helper functions,
which:
1. simplify code a bit
2. generalize nbd_read error descriptions, all starting with
   "Failed to read"
3. make it more difficult to forget to convert things from BE

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20190128165830.165170-1-vsementsov@virtuozzo.com>
[eblake: rename macro to DEF_NBD_READ_N and formatting tweaks;
checkpatch has false positive complaint]
Signed-off-by: Eric Blake <eblake@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/nbd/common.c b/nbd/common.c
index 41f5ed8..cc8b278 100644
--- a/nbd/common.c
+++ b/nbd/common.c
@@ -31,7 +31,7 @@ int nbd_drop(QIOChannel *ioc, size_t size, Error **errp)
     buffer = sizeof(small) >= size ? small : g_malloc(MIN(65536, size));
     while (size > 0) {
         ssize_t count = MIN(65536, size);
-        ret = nbd_read(ioc, buffer, MIN(65536, size), errp);
+        ret = nbd_read(ioc, buffer, MIN(65536, size), NULL, errp);
 
         if (ret < 0) {
             goto cleanup;