Re: [Qemu-devel] [PATCH] qemu-nbd: Ignore SIGPIPE

[Paolo Bonzini]

On 11/06/2017 14:37, Max Reitz wrote:
> qemu proper has done so for 13 years
> (8a7ddc38a60648257dc0645ab4a05b33d6040063), qemu-img and qemu-io have
> done so for four years (526eda14a68d5b3596be715505289b541288ef2a).
> Ignoring this signal is especially important in qemu-nbd because
> otherwise a client can easily take down the qemu-nbd server by dropping
> the connection when the server wants to send something, for example:
> 
> $ qemu-nbd -x foo -f raw -t null-co:// &
> [1] 12726
> $ qemu-io -c quit nbd://localhost/bar
> can't open device nbd://localhost/bar: No export with name 'bar' available
> [1]  + 12726 broken pipe  qemu-nbd -x foo -f raw -t null-co://
> 
> In this case, the client sends an NBD_OPT_ABORT and closes the
> connection (because it is not required to wait for a reply), but the
> server replies with an NBD_REP_ACK (because it is required to reply).
> 
> Signed-off-by: Max Reitz <address@hidden>
> ---
> I tried to find some other reproducer instead of using a qemu client
> (e.g. nping -c 1 --tcp-connect localhost -p 10809, which gives the same
> pattern of <FIN-ACK, >PSH-ACK, <RST as qemu-io) but to no avail. This
> only results in the write being successful and the next read failing;
> interestingly, sendmsg()'s man page states that EPIPE is only returned
> when the local end is closed. However, I have not found the NBD server
> to close that local end anywhere.
> 
> In any case, ignoring SIGPIPE is the right thing to do. We get an EPIPE
> anyway, and this is fully sufficient to let us know that the connection
> is dead.
> ---
>  qemu-nbd.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/qemu-nbd.c b/qemu-nbd.c
> index b7ab86b..b2eeedb 100644
> --- a/qemu-nbd.c
> +++ b/qemu-nbd.c
> @@ -580,6 +580,10 @@ int main(int argc, char **argv)
>      sa_sigterm.sa_handler = termsig_handler;
>      sigaction(SIGTERM, &sa_sigterm, NULL);
>  
> +#ifdef CONFIG_POSIX
> +    signal(SIGPIPE, SIG_IGN);
> +#endif
> +
>      module_call_init(MODULE_INIT_TRACE);
>      qcrypto_init(&error_fatal);
>  
> 

Queued, thanks.