From 1104d83c726d2b20f9cec7b99ab3570a2fdbd46d Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Wed, 8 Nov 2017 15:56:58 -0600 Subject: nbd-client: Refuse read-only client with BDRV_O_RDWR The NBD spec says that clients should not try to write/trim to an export advertised as read-only by the server. But we failed to check that, and would allow the block layer to use NBD with BDRV_O_RDWR even when the server is read-only, which meant we were depending on the server sending a proper EPERM failure for various commands, and also exposes a leaky abstraction: using qemu-io in read-write mode would succeed on 'w -z 0 0' because of local short-circuiting logic, but 'w 0 0' would send a request over the wire (where it then depends on the server, and fails at least for qemu-nbd but might pass for other NBD implementations). With this patch, a client MUST request read-only mode to access a server that is doing a read-only export, or else it will get a message like: can't open device nbd://localhost:10809/foo: request for write access conflicts with read-only export It is no longer possible to even attempt writes over the wire (including the corner case of 0-length writes), because the block layer enforces the explicit read-only request; this matches the behavior of qcow2 when backed by a read-only POSIX file. Fix several iotests to comply with the new behavior (since qemu-nbd of an internal snapshot, as well as nbd-server-add over QMP, default to a read-only export, we must tell blockdev-add/qemu-io to set up a read-only client). CC: qemu-stable@nongnu.org Signed-off-by: Eric Blake Message-Id: <20171108215703.9295-3-eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy --- tests/qemu-iotests/140 | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'tests/qemu-iotests/140') diff --git a/tests/qemu-iotests/140 b/tests/qemu-iotests/140 index f89d0d6..a8fc951 100755 --- a/tests/qemu-iotests/140 +++ b/tests/qemu-iotests/140 @@ -78,7 +78,7 @@ _send_qemu_cmd $QEMU_HANDLE \ 'arguments': { 'device': 'drv' }}" \ 'return' -$QEMU_IO_PROG -f raw -c 'read -P 42 0 64k' \ +$QEMU_IO_PROG -f raw -r -c 'read -P 42 0 64k' \ "nbd+unix:///drv?socket=$TEST_DIR/nbd" 2>&1 \ | _filter_qemu_io | _filter_nbd @@ -87,7 +87,7 @@ _send_qemu_cmd $QEMU_HANDLE \ 'arguments': { 'device': 'drv' }}" \ 'return' -$QEMU_IO_PROG -f raw -c close \ +$QEMU_IO_PROG -f raw -r -c close \ "nbd+unix:///drv?socket=$TEST_DIR/nbd" 2>&1 \ | _filter_qemu_io | _filter_nbd -- cgit v1.1