dbclient using 100% CPU

[Jamie Lokier]

I'm using dbclient on an ARM + uClinux device, and I see that it's
using 100% CPU although it has nothing to do.

The command looks like this:

    dbclient -T -i /root/.ssh/id_rsa.db 192.168.0.100 -R 10136:127.0.0.1:23 'while :; do echo keepalive; sleep 20; done'

The standard input and standard output are both /dev/null.  ( If
standard output is not /dev/null, I don't see 100% CPU, but the same
"select for read on standard output" behaviour described below occurs. )

The output of strace explains the 100% CPU:

    select(4, [1 3], [], NULL, {20, 0})     = 1 (in [1], left {20, 0})
    gettimeofday({1105499730, 917033}, NULL) = 0
    write(1, NULL, 0)                       = 0
    select(4, [1 3], [], NULL, {20, 0})     = 1 (in [1], left {20, 0})
    gettimeofday({1105499731, 117149}, NULL) = 0
    write(1, NULL, 0)                       = 0
    ... repeating ...

Why is it selecting for _read_ on the standard _output_ file
descriptor?  That looks like a bug to me.

The function setchannelfds() in common-channel.c may be the culprit.

The code and comments in setchannelfds() contradict the comments in
channel.h, concerning roles of channel->infd and channel->outfd:

	/* Stuff to put over the wire */
	if (channel->transwindow > 0) {
		if (channel->outfd >= 0) {
			FD_SET(channel->outfd, readfd);

	/* Stuff from the wire, to local program/shell/user etc */
	if ((channel->infd >= 0 && cbuf_getused(channel->writebuf) > 0 )
			|| channel->initconn) {
		FD_SET(channel->infd, writefd);

but:

	int infd; /* data to send over the wire */
	int outfd; /* data for consumption, what was in writebuf */

Thanks,
-- Jamie