On 25/01/2018 08:51, Klim Kireev wrote:
> The following behavior was observed for QEMU configured by libvirt
> to use guest agent as usual for the guests without virtio-serial
> driver (Windows or the guest remaining in BIOS stage).
>
> In QEMU on first connect to listen character device socket
> the listen socket is removed from poll just after the accept().
> virtio_serial_guest_ready() returns 0 and the descriptor
> of the connected Unix socket is removed from poll and it will
> not be present in poll() until the guest will initialize the driver
> and change the state of the serial to "guest connected".
>
> In libvirt connect() to guest agent is performed on restart and
> is run under VM state lock. Connect() is blocking and can
> wait forever.
> In this case libvirt can not perform ANY operation on that VM.
>
> The bug can be easily reproduced this way:
>
> Terminal 1:
> qemu-system-x86_64 -m 512 -device pci-serial,chardev=serial1 -chardev
> socket,id=serial1,path=/tmp/console.sock,server,nowait
> (virtio-serial and isa-serial also fit)
>
> Terminal 2:
> minicom -D unix\#/tmp/console.sock
> (type something and press enter)
> C-a x (to exit)
>
> Do 3 times:
> minicom -D unix\#/tmp/console.sock
> C-a x
>
> It needs 4 connections, because the first one is accepted by QEMU, then two
> are queued by
> the kernel, and the 4th blocks.
>
> The problem is that QEMU doesn't add a read watcher after succesful read
> until the guest device wants to acquire recieved data, so
> I propose to install a separate pullhup watcher regardless of
> whether the device waits for data or not.
>
> Signed-off-by: Klim Kireev <klim.kir...@virtuozzo.com>
> ---
> Changelog:
> v2: Remove timer as a redundant feature
>
> v3: Remove read call and return G_SOURCE_REMOVE
>
> v4: Move to GSource API
>
> v5: Fix git typos
>
> chardev/char-socket.c | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/chardev/char-socket.c b/chardev/char-socket.c
> index 77cdf487eb..a340af6cd3 100644
> --- a/chardev/char-socket.c
> +++ b/chardev/char-socket.c
> @@ -42,6 +42,7 @@ typedef struct {
> QIOChannel *ioc; /* Client I/O channel */
> QIOChannelSocket *sioc; /* Client master channel */
> QIONetListener *listener;
> + GSource *hup_source;
> QCryptoTLSCreds *tls_creds;
> int connected;
> int max_size;
> @@ -352,6 +353,12 @@ static void tcp_chr_free_connection(Chardev *chr)
> s->read_msgfds_num = 0;
> }
>
> + if (s->hup_source != NULL) {
> + g_source_destroy(s->hup_source);
> + g_source_unref(s->hup_source);
> + s->hup_source = NULL;
> + }
> +
> tcp_set_msgfds(chr, NULL, 0);
> remove_fd_in_watch(chr);
> object_unref(OBJECT(s->sioc));
> @@ -455,6 +462,15 @@ static gboolean tcp_chr_read(QIOChannel *chan,
> GIOCondition cond, void *opaque)
> return TRUE;
> }
>
> +static gboolean tcp_chr_hup(QIOChannel *channel,
> + GIOCondition cond,
> + void *opaque)
> +{
> + Chardev *chr = CHARDEV(opaque);
> + tcp_chr_disconnect(chr);
> + return G_SOURCE_REMOVE;
> +}
> +
> static int tcp_chr_sync_read(Chardev *chr, const uint8_t *buf, int len)
> {
> SocketChardev *s = SOCKET_CHARDEV(chr);
> @@ -528,6 +544,12 @@ static void tcp_chr_connect(void *opaque)
> tcp_chr_read,
> chr, chr->gcontext);
> }
> +
> + s->hup_source = qio_channel_create_watch(s->ioc, G_IO_HUP);
> + g_source_set_callback(s->hup_source, (GSourceFunc)tcp_chr_hup,
> + chr, NULL);
> + g_source_attach(s->hup_source, chr->gcontext);
> +
> qemu_chr_be_event(chr, CHR_EVENT_OPENED);
> }
>
>
Queued, thanks.
Paolo
