Hi, Marc-André and Michael
On 07/09/2026 14:32, Michael S. Tsirkin wrote:
On Mon, Sep 07, 2026 at 06:18:39PM +0400, Marc-André Lureau wrote:
Hi
On Mon, Sep 7, 2026 at 5:35 PM Michael S. Tsirkin <[email protected]> wrote:
On Mon, Sep 07, 2026 at 05:22:43PM +0400, Marc-André Lureau wrote:
maybe just avoid stdbuf completely.
i don't remember why we use it, but it looks like merely to
disable buffering for stdout?
If so:
setvbuf(stdout, NULL, _IONBF, 0);
will do just that with no asan issues.
That requires modifying vhost-user-bridge, not sure that's what we want.
thanks
why not? it's not like it's a facility useful outside of testing qemu.
If we were we'd probably disable stdout printout completely.
Since the test redirects stderr to stdout, I guess the log is
fully-buffered for stdout and unbuffered for stderr, and we see stderr
log lines in the file log before the others. If we call
setvbuf(stdout, NULL, _IONBF, 0) early, we probably will get
interleaved stream output, but probably broken lines...
We can also just change that macro to write to stderr.
Tbh, I don't
have much motivation to check or fix this, I would just like the test
to be green or skipped when built with ASAN. The current workaround is
quite ok. If you prefer setvbuf() in vhost-user-bridge.c, I am okay
too.
Yodel, wdyt?
Apologies for the delayed response, and thanks for finding,
reporting, and addressing the problematic interaction
between stdbuf and ASAN.
I have implemented Michael's suggestion to modify the DPRINT
macro to write to stderr and can attest that the log lines
are properly interleaved even in the absence of stdbuf.
If there are no objections, I'll submit the patch shortly.
Below is a preview.
Thanks,
Yodel
-- >8 --
diff --git a/contrib/vhost-user-bridge/vhost-user-bridge.c
b/contrib/vhost-user-bridge/vhost-user-bridge.c
index 3f0fd0fa49..a6f7ec226c 100644
--- a/contrib/vhost-user-bridge/vhost-user-bridge.c
+++ b/contrib/vhost-user-bridge/vhost-user-bridge.c
@@ -41,7 +41,7 @@
#define DPRINT(...) \
do { \
if (VHOST_USER_BRIDGE_DEBUG) { \
- printf(__VA_ARGS__); \
+ fprintf(stderr, __VA_ARGS__); \
} \
} while (0)
diff --git a/tests/functional/x86_64/test_vhost_user_bridge.py
b/tests/functional/x86_64/test_vhost_user_bridge.py
index c36c625420..5e1db48884 100755
--- a/tests/functional/x86_64/test_vhost_user_bridge.py
+++ b/tests/functional/x86_64/test_vhost_user_bridge.py
@@ -76,12 +76,6 @@ def configure_vm(self, ud_socket_path, lport, rport,
hostfwd_port, tftpdir):
def assemble_vubr_args(self, vubr_path, ud_socket_path, lport, rport):
vubr_args = []
- if (stdbuf_path := which("stdbuf")) is None:
- self.log.info("Could not find stdbuf: vhost-user-bridge "
- "log lines may appear out of order")
- else:
- vubr_args += [stdbuf_path, "-o0", "-e0"]
-
vubr_args += [vubr_path, "-u", f"{ud_socket_path}",
"-l", f"127.0.0.1:{lport}", "-r",
f"127.0.0.1:{rport}"]
