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 needed to properly handle non-blocking I/O, to replace the workaround done in commit 6ab3fc32ea640026726bc5f9f4db622d0954fb8a Author: Daniel P. Berrange <berra...@redhat.com> Date: Tue Sep 6 14:56:04 2016 +0100 hw: replace most use of qemu_chr_fe_write with qemu_chr_fe_write_all Some places in the chardev code in fact alreadying use watches for a few actions, but then use sync i/o for other stuff. So using events will give a consistent model. Once you're doing proper event driven I/O, then detecting hangup is also trivial. IOW, I don't think we need add anything to QIOChannel - just continue to cleanup the chardev backends to better use the functionality that already exists. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|