nbd: Use new qio_channel_*_all() functions

Rather than open-coding our own read/write-all functions, we
can make use of the recently-added qio code.  It slightly
changes the error message in one of the iotests.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20170905191114.5959-4-eblake@redhat.com>
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>

nbd/common.c

@@ -20,51 +20,6 @@
 #include "qapi/error.h"
 #include "nbd-internal.h"
 
-/* nbd_wr_syncv
- * The function may be called from coroutine or from non-coroutine context.
- * When called from non-coroutine context @ioc must be in blocking mode.
- */
-ssize_t nbd_rwv(QIOChannel *ioc, struct iovec *iov, size_t niov, size_t length,
-                bool do_read, Error **errp)
-{
-    ssize_t done = 0;
-    struct iovec *local_iov = g_new(struct iovec, niov);
-    struct iovec *local_iov_head = local_iov;
-    unsigned int nlocal_iov = niov;
-
-    nlocal_iov = iov_copy(local_iov, nlocal_iov, iov, niov, 0, length);
-
-    while (nlocal_iov > 0) {
-        ssize_t len;
-        if (do_read) {
-            len = qio_channel_readv(ioc, local_iov, nlocal_iov, errp);
-        } else {
-            len = qio_channel_writev(ioc, local_iov, nlocal_iov, errp);
-        }
-        if (len == QIO_CHANNEL_ERR_BLOCK) {
-            /* errp should not be set */
-            assert(qemu_in_coroutine());
-            qio_channel_yield(ioc, do_read ? G_IO_IN : G_IO_OUT);
-            continue;
-        }
-        if (len < 0) {
-            done = -EIO;
-            goto cleanup;
-        }
-
-        if (do_read && len == 0) {
-            break;
-        }
-
-        iov_discard_front(&local_iov, &nlocal_iov, len);
-        done += len;
-    }
-
- cleanup:
-    g_free(local_iov_head);
-    return done;
-}
-
 /* Discard length bytes from channel.  Return -errno on failure and 0 on
  * success */
 int nbd_drop(QIOChannel *ioc, size_t size, Error **errp)