From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <13426df10712171736i60f181aax4fdf2cf57594fa87@mail.gmail.com>
Date: Mon, 17 Dec 2007 17:36:43 -0800
From: "ron minnich" <rminnich@gmail.com>
To: "Fans of the OS Plan 9 from Bell Labs" <9fans@cse.psu.edu>
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Subject: [9fans] a question on APE
Topicbox-Message-UUID: 1c015a2a-ead3-11e9-9d60-3106f5b1d025

we're doing some work here with Andrey's port of ssh2. It *almost*
works. But I'm seeing a stack trace I don't understand.

I can't give you all the details -- it's ssh, therefore it is pretty
awful -- but here is the short form: There is a proc called fromnet()
which has this inner loop:
	for(;;){
		if((n = libssh2_channel_read(c, buf, Bufsize)) > 0)
			write(1, buf, n);
		else
			goto Donenet;
	}

When this proc is entered, ape has forked off two procs to handle the
fd 'c'. From the fromnet function, we see the libssh2_channel_read
does a select. here is where I get confused. The stk() for the two
procs looks like this:
pread()+0x7 /sys/src/libc/9syscall/pread.s:5
read(fd=0x5,buf=0x110414,n=0x1000)+0x2f /sys/src/libc/9sys/read.c:7
recv(flags=0x0,fd=0x5,a=0x110414,n=0x1000)+0x3e /sys/src/ape/lib/bsd/send.c:30
libssh2_packet_read(session=0x1102f8)+0x176
/usr/bootes/libssh2/libssh2-0.18/src/transport.c:326
libssh2_channel_read_ex(channel=0x114460,buflen=0x1000,stream_id=0x0,buf=0xdfffdee8)+0x2a7
/usr/bootes/libssh2/libssh2-0.18/src/channel.c:1442
fromnet(c=0x114460,s=0x1102f8)+0x2e
/usr/bootes/libssh2/libssh2-0.18/clients/ssh2.c:75
main(argc=0x2,argv=0xdfffef94)+0x47c
/usr/bootes/libssh2/libssh2-0.18/clients/ssh2.c:253
_main+0x31 /sys/src/libc/386/main9.s:16

The the read on fd 5. That's the socket. Here is the other proc.

_PREAD()+0x7 /sys/src/ape/lib/ap/syscall/_PREAD.s:5
_READ(fd=0x5,buf=0x600003c,n=0x2000)+0x2f /sys/src/ape/lib/ap/plan9/9read.c:10
_copyproc(b=0x6000028,fd=0x5)+0x86 /sys/src/ape/lib/ap/plan9/_buf.c:166
_startbuf(fd=0x5)+0x1dd /sys/src/ape/lib/ap/plan9/_buf.c:107
select(timeout=0xdfffde90,rfds=0xdfffde80,wfds=0x0,efds=0x0,nfds=0x6)+0xe9
/sys/src/ape/lib/ap/plan9/_buf.c:292
libssh2_waitsocket(session=0x1102f8,seconds=0x0)+0x7b
/usr/bootes/libssh2/libssh2-0.18/src/packet.c:1054
libssh2_channel_read_ex(channel=0x114460,buflen=0x1000,stream_id=0x0,buf=0xdfffdee8)+0x69
/usr/bootes/libssh2/libssh2-0.18/src/channel.c:1408
fromnet(c=0x114460,s=0x1102f8)+0x2e
/usr/bootes/libssh2/libssh2-0.18/clients/ssh2.c:75
main(argc=0x2,argv=0xdfffef94)+0x47c
/usr/bootes/libssh2/libssh2-0.18/clients/ssh2.c:253
_main+0x31 /sys/src/libc/386/main9.s:16

ok, I think this stack is a bit messed up, since I don't see how we
can have the coyproc in the call chain from select(), but ... is it?

I realize there is very little information here, sorry ... here's what
is bothering me. It seems we have two procs hanging on a read on fd 5.
I think the copyproc and some other proc are in conflict but ... I am
unsure. The problems we are seeing might be explained by the wrong
proc grabbing output at the wrong time -- it feels like a race
condition. And acid trips we can take to hammer this one down?

Anyone ever done a select on a socket in ape?