[Qemu-devel] [PATCH 1/2] nbd: Don't export a block device with no medium.

[Hani Benhabiles <kroosec@gmail.com>]

The device is exported with erroneous values and can't be read.

Before the patch:
$ sudo nbd-client localhost -p 10809 /dev/nbd0 -name floppy0
Negotiation: ..size = 17592186044415MB
bs=1024, sz=18446744073709547520 bytes

$ sudo mount /dev/nbd0 /mnt/tmp/
mount: block device /dev/nbd0 is write-protected, mounting read-only
mount: /dev/nbd0: can't read superblock

After the patch:
(qemu) nbd_server_add ide0-hd0
(qemu) nbd_server_add floppy0
Device 'floppy0' has no medium

Signed-off-by: Hani Benhabiles <hani@linux.com>
---
 blockdev-nbd.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/blockdev-nbd.c b/blockdev-nbd.c
index 922cf56..a700d52 100644
--- a/blockdev-nbd.c
+++ b/blockdev-nbd.c
@@ -91,6 +91,10 @@ void qmp_nbd_server_add(const char *device, bool has_writable, bool writable,
         error_set(errp, QERR_DEVICE_NOT_FOUND, device);
         return;
     }
+    if (!bdrv_is_inserted(bs)) {
+        error_set(errp, QERR_DEVICE_HAS_NO_MEDIUM, device);
+        return;
+    }
 
     if (!has_writable) {
         writable = false;
-- 
1.8.3.2