Bug#977562: systemd: Incorrect order of agetty arguments in serial-getty at ttyS0.service definition file

[Karel Zak]

On Thu, Jan 14, 2021 at 05:26:40PM +0100, Michael Biebl wrote:
> Karel,
> 
> sorry for poking you directly: Could you weigh in here?

agetty accepts both:

        agetty --help

        Usage:
         agetty [options] <line> [<baud_rate>,...] [<termtype>]
         agetty [options] <baud_rate>,... <line> [<termtype>]

and code differentiates between these variants by digits, if the string
contains only "0123456789," than it <baud_rate>.

> > On 1/14/21 3:06 PM, Michael Biebl wrote:
> > > Am 19.12.20 um 16:47 schrieb Andreas Henriksson:
> > > > Control: tags -1 + moreinfo
> > > > 
> > > > On Wed, Dec 16, 2020 at 11:39:06PM +0100, Michael Biebl wrote:
> > > > > Am 16.12.20 um 20:49 schrieb MK:
> > > > > > Package: systemd
> > > > > > Version: 241-7~deb10u5
> > > > > > Severity: normal
> > > > [...]
> > > > > > Incorrect order of arguments to agetty in the
> > > > > > serial-getty at ttyS0.service
> > > > > > unit file.
> > > > > > 
> > > > > > It is:
> > > > > > 
> > > > > > ExecStart=/sbin/agetty --autologin root -8 --keep-baud
> > > > > > 115200,38400,9600 ttyS0 xterm-256color
> > > > > > 
> > > > > > 
> > > > > > While it should be like:
> > > > > > 
> > > > > > ExecStart=/sbin/agetty --autologin root -8 --keep-baud
> > > > > > ttyS0 115200 xterm-256color
> > > > [...]
> > > > > According to the examples in man agetty, both should work.
> > > > > 
> > > > > Andreas, can you comment here?
> > > > > If what MK is saying, should the "EXAMPLE" section in man
> > > > > agetty be updated?

I think the man page is correct.

> > > > I don't really have much prior knowledge about *getty, but in my past
> > > > experience with other util-linux tools it is often the case that
> > > > (likely for historical reasons/compatibility) the arguments that
> > > > doesn't come in a dash-form is attempted to be accepted in either
> > > > order based on guessing which one was specified. In my past experience
> > > > something that was guessable in the past might in later years become
> > > > sometimes impossible to correctly guess right, so sticking with
> > > > what synopsis describes is usually the safest as far as I'm concerned.
> > > > 
> > > > In the agetty case, the guessing is done here:
> > > > https://sources.debian.org/src/util-linux/2.36.1-2/term-utils/agetty.c/#L897
> > > > 
> > > > 
> > > > is_speed basically checks if the current argument only consists of
> > > > either 0-9 or ','.

Yes

> > > > It is not obvious to me how it could go wrong in the example originally
> > > > described in this bug report.
> > > > 
> > > > Please also note that for example sysvinit's inittab also uses getty
> > > > with arguments in both orders.
> > > > 
> > > > Simply it should work either way.
> > > > 
> > > > Please also note that the argument order is not the only thing changed.
> > > > It was also changed from specifying 3 speeds to only 1.
> > > > 
> > > > Maybe the real issue here is that line speed detection isn't working?
> > > > I'd appreciate if the bug reporter could dive a bit deeper into the
> > > > problem.

Yes.

 Karel



-- 
 Karel Zak  <kzak at redhat.com>
 http://karelzak.blogspot.com