[Qemu-devel] [PATCH] qemu-char: Do not disconnect when there's data for reading
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
CC: Nikolay Nikolaev
CC: Anthony Liguori
Signed-off-by: Zifei Tong
---
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;
--
2.1.0
Re: [Qemu-devel] [PATCH] qemu-char: Do not disconnect when there's data for reading
Friendly ping.
Also CC to qemu-trivial.
On Sun, Sep 7, 2014 at 8:24 PM, Zifei Tong wrote:
> 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
> CC: Nikolay Nikolaev
> CC: Anthony Liguori
> Signed-off-by: Zifei Tong
> ---
> 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;
> --
> 2.1.0
>
Re: [Qemu-devel] [PATCH] qemu-char: Do not disconnect when there's data for reading
Cc'ing Gerd for additional chardev expertise.
Zifei Tong 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.
Reproduced.
Is this a regression caused by command 812c105?
> CC: Kirill Batuzov
> CC: Nikolay Nikolaev
> CC: Anthony Liguori
> Signed-off-by: Zifei Tong
> ---
> 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;
Kirill, you added the code being changed. Could you review the patch?
Re: [Qemu-devel] [PATCH] qemu-char: Do not disconnect when there's data for reading
On Tue, Sep 16, 2014 at 2:06 PM, Markus Armbruster wrote:
> Cc'ing Gerd for additional chardev expertise.
>
> Zifei Tong 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.
>
> Reproduced.
>
> Is this a regression caused by command 812c105?
The first bad commit is cdaa86 ("Add G_IO_HUP handler for socket
chardev"), which is reverted and reimplemented by 812c105.
>> CC: Kirill Batuzov
>> CC: Nikolay Nikolaev
>> CC: Anthony Liguori
>> Signed-off-by: Zifei Tong
>> ---
>> 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;
>
> Kirill, you added the code being changed. Could you review the patch?
Re: [Qemu-devel] [PATCH] qemu-char: Do not disconnect when there's data for reading
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 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
> CC: Nikolay Nikolaev
> CC: Anthony Liguori
> Signed-off-by: Zifei Tong
> ---
> 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;
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.
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
Re: [Qemu-devel] [PATCH] qemu-char: Do not disconnect when there's data for reading
On Tue, Sep 16, 2014 at 11:30 PM, Kirill Batuzov 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 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
>> CC: Nikolay Nikolaev
>> CC: Anthony Liguori
>> Signed-off-by: Zifei Tong
>> ---
>> 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
