On Tue, Sep 16, 2014 at 11:30 PM, Kirill Batuzov <batuz...@ispras.ru> wrote: > On Tue, 16 Sep 2014, Markus Armbruster wrote: > >> >> Kirill, you added the code being changed. Could you review the patch? >> > > I'll try but this is more about GIOConditions which I do not understand > well. See below. > > Zifei Tong <zifeit...@gmail.com> writes: > >> After commit 812c1057f6175ac9a9829fa2920a2b5783814193 (Handle G_IO_HUP >> in tcp_chr_read for tcp chardev), the connection is disconnected when in >> G_IO_HUP condition. >> >> However, it's possible that the channel is in G_IO_IN condition at the >> same time, meaning there is data for reading. In that case, the >> remaining data is not handled. >> >> I saw a related bug when running socat in write-only mode, with >> >> $ echo "quit" | socat -u - UNIX-CONNECT:qemu-monitor >> >> the monitor won't not run the 'quit' command. >> CC: Kirill Batuzov <batuz...@ispras.ru> >> CC: Nikolay Nikolaev <n.nikol...@virtualopensystems.com> >> CC: Anthony Liguori <aligu...@amazon.com> >> Signed-off-by: Zifei Tong <zifeit...@gmail.com> >> --- >> qemu-char.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/qemu-char.c b/qemu-char.c >> index 1a8d9aa..5018c3a 100644 >> --- a/qemu-char.c >> +++ b/qemu-char.c >> @@ -2706,7 +2706,7 @@ static gboolean tcp_chr_read(GIOChannel *chan, >> GIOCondition cond, void *opaque) >> uint8_t buf[READ_BUF_LEN]; >> int len, size; >> >> - if (cond & G_IO_HUP) { >> + if (!(cond & G_IO_IN) && (cond & G_IO_HUP)) { >> /* connection closed */ >> tcp_chr_disconnect(chr); >> return TRUE;
Hi Kirill, Thanks for your review and detailed analysis. > I've tried running the above code and watching in debugger what is > happening. I wanted to know that tcp_chr_disconnect is called properly > so I replaced the 'quit' command with 'help'. From the way code works I > have a feeling that we are using some undocumented linux-specific > behaviour here. > > What I saw: > - Sometimes all three (G_IO_IN, G_IO_HUP and G_IO_ERR) conditions are > asserted, sometimes only two of them (G_IO_IN and G_IO_HUP). > - G_IO_IN is *never* de-asserted. Even after all data is depleted it is > still up. > - When G_IO_ERR is asserted and all data have been read one call to > tcp_chr_recv returns -1. Subsequent calls return 0. > > GIOCondition behaviour in corner cases is puzzling and can differ from OS > to OS (commit 812c105 is an example, there also were freebsd-specific > bugfixes if I remember correctly). > > I suggest we remove condition checks completely and use more reliable > and better documented source of information - return value of > tcp_chr_recv (which is just return value of recvmsg). All we need to do > is to handle 'size < 0' and not forget about EAGAIN case. This sounds good to me. I'll send a V2 patch based on this. Thanks, Zifei > Currently we have a mix of GLib conditions and POSIX return values to > handle all cases and we can not do it with GLib alone (I do not know a > way to tell if there is data in channel or not when G_IO_HUP is asserted). > > All these problems were before this patch, but I think it is better to > fix it once than add patch over patch fighting GIOCondition's weird > behaviour. > > -- > Kirill