Re: [Sshpass-devel] SIGCHLD blocking?

[Martin G. <omg...@gm...>]

Hi Shachar, thanks for the answer.

2018-07-05 14:39 GMT-03:00 Shachar Shemesh <sh...@sh...>:
> In sshpass's particular case, however, you are right - there is a race in
> the use case you mention. The reason there is a case is not because the
> child might send a SIGCHLD before we block it. It is because we call
> "waitpid" after we call pselect (thus, if the signal arrives before we block
> it, we won't get around to releasing the process until the select returns
> for whatever other reason).

Why would pselect return, other than if there happens to be some
output on the term? I don't fully understand the PTY magic here, so
bear with me.

While we're at that, there's a comment saying that handleoutput will
return a negative value if the slave end of the PTY is closed.
However, looking at handleoutput I couldn't find a case where the
return value would be negative. Am I missing something?

And since it can't hurt to ask: I noticed there's a check for
'terminate' at the beginning of the do-while loop. If terminate is not
zero, we'll do wait_id=waitpid( childpid, &status, 0 );. Is this just
a way to make sure we wait on the child process in case SSH (or
whatever program we end up running) errored out? Also, what if pselect
returns -1 for some reason other than us getting a signal (e.g.
ENOMEM)? Wouldn't we be stuck in an infinite loop since the WNOHANG
waitpid would always set wait_id to zero?