nbd/client: refactor nbd_read_eof

Refactor nbd_read_eof to return 1 on success, 0 on eof, when no
data was read and <0 for other cases, because returned size of
read data is not actually used.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20170804151440.320927-3-vsementsov@virtuozzo.com>
[eblake: tweak function comments, rebase to test 083 enhancements]
Signed-off-by: Eric Blake <eblake@redhat.com>

1 files changed, 24 insertions, 9 deletions

diff --git a/nbd/nbd-internal.h b/nbd/nbd-internal.h
index 396ddb4d3e..03549e3f39 100644
--- a/nbd/nbd-internal.h
+++ b/nbd/nbd-internal.h
@@ -77,21 +77,36 @@
 #define NBD_ESHUTDOWN  108
 
 /* nbd_read_eof
- * Tries to read @size bytes from @ioc. Returns number of bytes actually read.
- * May return a value >= 0 and < size only on EOF, i.e. when iteratively called
- * qio_channel_readv() returns 0. So, there is no need to call nbd_read_eof
- * iteratively.
+ * Tries to read @size bytes from @ioc.
+ * Returns 1 on success
+ *         0 on eof, when no data was read (errp is not set)
+ *         negative errno on failure (errp is set)
  */
-static inline ssize_t nbd_read_eof(QIOChannel *ioc, void *buffer, size_t size,
-                                   Error **errp)
+static inline int nbd_read_eof(QIOChannel *ioc, void *buffer, size_t size,
+                               Error **errp)
 {
     struct iovec iov = { .iov_base = buffer, .iov_len = size };
+    ssize_t ret;
+
     /* Sockets are kept in blocking mode in the negotiation phase.  After
      * that, a non-readable socket simply means that another thread stole
      * our request/reply.  Synchronization is done with recv_coroutine, so
      * that this is coroutine-safe.
      */
-    return nbd_rwv(ioc, &iov, 1, size, true, errp);
+
+    assert(size);
+
+    ret = nbd_rwv(ioc, &iov, 1, size, true, errp);
+    if (ret <= 0) {
+        return ret;
+    }
+
+    if (ret != size) {
+        error_setg(errp, "End of file");
+        return -EINVAL;
+    }
+
+    return 1;
 }
 
 /* nbd_read
@@ -100,9 +115,9 @@ static inline ssize_t nbd_read_eof(QIOChannel *ioc, void *buffer, size_t size,
 static inline int nbd_read(QIOChannel *ioc, void *buffer, size_t size,
                            Error **errp)
 {
-    ssize_t ret = nbd_read_eof(ioc, buffer, size, errp);
+    int ret = nbd_read_eof(ioc, buffer, size, errp);
 
-    if (ret >= 0 && ret != size) {
+    if (ret == 0) {
         ret = -EINVAL;
         error_setg(errp, "End of file");
     }