tests: virtio-9p: add FLUSH operation test

The idea is to send a victim request that will possibly block in the
server and to send a flush request to cancel the victim request.

This patch adds two test to verifiy that:
- the server does not reply to a victim request that was actually
  cancelled
- the server replies to the flush request after replying to the
  victim request if it could not cancel it

9p request cancellation reference:

http://man.cat-v.org/plan_9/5/flush

Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
(groug, change the test to only write a single byte to avoid
        any alignment or endianess consideration)

1 files changed, 7 insertions, 0 deletions

diff --git a/hw/9pfs/9p-synth.h b/hw/9pfs/9p-synth.h
index a74032d..af7a993 100644
--- a/hw/9pfs/9p-synth.h
+++ b/hw/9pfs/9p-synth.h
@@ -55,4 +55,11 @@ int qemu_v9fs_synth_add_file(V9fsSynthNode *parent, int mode,
 #define QTEST_V9FS_SYNTH_LOPEN_FILE "LOPEN"
 #define QTEST_V9FS_SYNTH_WRITE_FILE "WRITE"
 
+/* Any write to the "FLUSH" file is handled one byte at a time by the
+ * backend. If the byte is zero, the backend returns success (ie, 1),
+ * otherwise it forces the server to try again forever. Thus allowing
+ * the client to cancel the request.
+ */
+#define QTEST_V9FS_SYNTH_FLUSH_FILE "FLUSH"
+
 #endif