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Re: channel_write will fail if large amount of data are being written (0.4 branch)


Vic,

Sorry I just realized I did not finish and sent the email in which I suggested you to do so. Good thing it resolved your issue.

Regards,

Aris

Vic Lee a écrit :
Hi Aris,

It seems it's ok after I remove the ssh_set_blocking call. So probably
we don't need this patch for 0.4.

Thanks,

Vic

On Sat, 2010-01-23 at 01:13 +0800, Vic Lee wrote:
Hi Aris,

It's the ssh_set_blocking() call in session.c. Maybe I shouldn't use it?
If I don't set blocking to false, will there be any impact on
channel_read_nonblocking?

I also attach a patch which works for me, though I am not very sure if I
am doing the right thing here.

Thanks,

Vic

On Thu, 2010-01-21 at 22:22 +0100, Aris Adamantiadis wrote:
Hi Vic,

Could you try to get a backtrace at this place ?
I wonder why ssh_socket_nonblocking_flush is called. I put a breakpoint on this function and was not able to trigger it using samplessh. Could you also check session->blocking value ? normaly it's set to 1 in ssh_new and I could not find any other place where it's changed.

Thanks,

Aris

Vic Lee a écrit :
Hi,

I found another bug in channel_write() which make it fail to tunnel an
xterm over SSH.

According to the description, channel_write() is a blocking write until
all data written or until error. However, in the following call
sequence:

channel_write -> packet_send -> packet_send2 -> packet_write ->
packet_flush (at packet.c:456), it uses a non-blocking call:

  rc = packet_flush(session, 0);

which will almost always return SSH_AGAIN if large amount of data are
being flushed, and SSH_AGAIN will eventually returned by packet_send.
However, when channel_write calls packet_send it does not check for
SSH_AGAIN and simply think anything other than SSH_OK is an error.

This bug makes it impossible to tunnel an xterm (it's funny somehow
xterm has large data transmit). I temporarily change the packet_flush to
a blocking call fix the issue. But I think a right patch should be on
channel_write, checking SSH_AGAIN.

Your comments?

Thanks,

Vic








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