On 11/07/2017 14:37, Daniel P. Berrange wrote: > On Tue, Jul 11, 2017 at 02:21:08PM +0200, Paolo Bonzini wrote: >> On 11/07/2017 11:15, Daniel P. Berrange wrote: >>> On Tue, Jul 11, 2017 at 10:30:14AM +0200, Paolo Bonzini wrote: >>>> On 11/07/2017 13:47, Peng Hao wrote: >>>>> Parallel device don't register be->chr_can_read function, but remote >>>>> disconnect event is handled in chr_read.So connected parallel device >>>>> can not detect remote disconnect event. The chardevs with >>>>> chr_can_read=NULL >>>>> has the same problem. >>>>> >>>>> Signed-off-by: Peng Hao <peng.h...@zte.com.cn> >>>>> Reviewed-by: Wang Yechao <wang.yechao...@zte.com.cn> >>>>> --- >>>>> chardev/char-socket.c | 11 +++++++++++ >>>>> chardev/char.c | 10 ++++++++++ >>>>> include/chardev/char.h | 9 +++++++++ >>>>> 3 files changed, 30 insertions(+) >>>>> >>>>> diff --git a/chardev/char-socket.c b/chardev/char-socket.c >>>>> index ccc499c..aa44f8f 100644 >>>>> --- a/chardev/char-socket.c >>>>> +++ b/chardev/char-socket.c >>>>> @@ -139,6 +139,9 @@ static int tcp_chr_read_poll(void *opaque) >>>>> return 0; >>>>> } >>>>> s->max_size = qemu_chr_be_can_write(chr); >>>>> + if (qemu_chr_null_be_can_read(chr)) { >>>>> + return 1; >>>>> + } >>>>> return s->max_size; >>>>> } >>>>> >>>>> @@ -422,6 +425,14 @@ static gboolean tcp_chr_read(QIOChannel *chan, >>>>> GIOCondition cond, void *opaque) >>>>> uint8_t buf[CHR_READ_BUF_LEN]; >>>>> int len, size; >>>>> >>>>> + if (qemu_chr_null_be_can_read(chr)) { >>>>> + size = tcp_chr_recv(chr, (void *)buf, CHR_READ_BUF_LEN); >>>> >>>> It would be better not to destroy data in the channel, because the >>>> device could set handlers later. >>>> >>>> Daniel, maybe QIOChannel could have a function to check for hung-up >>>> channels and return a bool? For file descriptors it would poll the file >>>> descriptor and check for POLLHUP, while other channels would have a more >>>> or less obvious implementation. >>> >>> IMHO the chardev code all needs to switch over to using even driven I/O >>> using the qio_channel_add_watch() function. >> >> This is a slightly different case; qio_channel_add_watch() is for the >> write side, while in this case we're concerned with the read side. >> >> The read-side watch is managed automatically by common chardev code. >> I'll see if we can change that code to set up a G_IO_HUP watch in >> addition to G_IO_IN. > > NB You don't ever need to use G_IO_HUP as an explicit input flag - poll() > will always report G_IO_HUP if you asked it to monitor for G_IO_IN.
Right, but in this case we don't want to monitor G_IO_IN, because there is no listener. The parallel port is a special case but actually the same would happen for any other device whose can_read callback can return zero. Some Unix variants require you to specify G_IO_HUP in the events (FreeBSD), others don't (Linux). Paolo