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Date: Thu,  2 Sep 2010 15:24:49 -0400
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Subject: Re: [9fans] P9p on Fedora 12
From: Russ Cox <rsc@swtch.com>
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
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On Mon, Aug 30, 2010 at 7:22 PM, Charles Forsyth <forsyth@terzarima.net> wr=
ote:
> in rcinputproc
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0s =3D setecho(sfd,=
 0);
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0if(write(rcfd, pai=
r.s, pair.ns) < 0)
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0threadexitsall(nil);
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0if(s)
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0setecho(sfd, s);
>
> there's a race between setting echo off, writing to rcfd, resetting echo =
and
> the reader of the other side of rcfd. a sleep(1) before if(s) makes it le=
ss frequent
> because the reader gets to read the data in the right mode.
> i haven't really looked at what linux is doing that allows that,
> or what changed between revisions.
>
> it's not my observation, it was on a list or issue comment somewhere,
> presumably for p9p. i can't find the bookmark.

thanks for this.  sleep(1) helped only rarely,
sleep(10) helps most of the time.  unfortunately
then there's a race between the invoked program
turning off echo and 9term turning it back on.
so "sudo sh" is pretty likely to echo the password
with the sleep in there.

what a mess.

russ