[Toybox] ps -t is cheating.

[Rob Landley]

On 10/19/2015 11:40 PM, Isaac Dunham wrote:
> On Mon, Oct 19, 2015 at 12:09:17AM -0500, Rob Landley wrote:
>> So posix says this:
>>
>> -t  termlist
>>   Write information for processes associated with terminals given in
>>   termlist. The application shall ensure that the termlist is a single
>>   argument in the form of a <blank> or <comma>-separated list. Terminal
>>   identifiers shall be given in an implementation-defined format. [XSI]
>>   [Option Start]  On XSI-conformant systems, they shall be given in one
>>   of two forms: the device's filename (for example, tty04) or, if the
>>   device's filename starts with tty, just the identifier following the
>>   characters tty (for example, "04" ). [Option End]
>>
>> And once again posix is somewhere back before the 1980's because
>> pseudo-terminals do not start with "/dev/tty". In the case of linux,
>> they've been /dev/pts/12 since, apparently, 1998.
> 
> VTs start with /dev/tty, as do all interfaces that are theoretically
> serial-based. Note that 'if'.
> 
> /dev/pts is actually the result of another part of POSIX (posix_openpt & co.)

There's a kernel .config option for legacy "unix98" ptys...

>> The ps man page says:
>>
>>   -t ttylist
>>        Select by tty.  This selects the processes associated with the
>>        terminals given in ttylist.  Terminals (ttys, or screens for
>>        text output) can be specified in several forms: /dev/ttyS1,
>>        ttyS1, S1.  A plain "-" may be used to select processes not
>>        attached to any terminal.
>>
>> Which is, once again, outright lying, because "-t 41" matches pts/41 but
>> -t 5 does _not_ match tty5. You have to say "-t tty5" to get the getty
>> instance on there.
>>
>> Meanwhile procutils "ps -t pts/41" works as does "ps -t pts/../tty5"
>> which is just _creepy_ and I'm not doing that bit. And -tty S0 is of
>> course /dev/ttyS0 not /dev/pts/S0.
>>
>> I pine for a spec that means something,
>>
>> Rob
>>
>> P.S.  Once again, the hard part is writing help text so ps --help can
>> explain the expected behavior succinctly. Yeah, I can do that, but how
>> do I explain it in a way that makes it sound intentional: -t ## is a pts
>> (unless maybe there isn't one? Does it fall back to tty5 if there's no
>> pts5? Hard to test right now because I've got /dev/pts/68 but only
>> /dev/tty63). Grrr. STOP TRYING TO BE CLEVER IN WAYS YOU DON'T EXPLAIN TO
>> YOUR USERS IN THE MAN PAGE. Right special case "-t number" to be pts/
>> instead of tty, accept pts/ to _not_ mean implicit tty prefix...
> 
> accept the following:
> * filenames relative to /dev

ps -t urandom

Yup, it took it.

> * filenames relative to /dev/pts

Like /dev/pts/../zero?

Oddly it doesn't seem to like symlinks. ln -s /dev/urandom 1234 neither
"ps -t 1234" or "ps -t ./1234" go through. But if I "cp -a /dev/zero"
zero and then "ps -t ./zero"...

Ah. 'mv zero zzero" then "ps -t ./zzero" and it won't find it, the
problem is it forces relative paths to be vs /dev (but doesn't stop you
from .. back out of them, so "ps -t ../$HOME/zzero" finds it.

What a mess.

> * fallback to "/dev/tty<arg>".
> No need to special case numbers.

The reference question "What does busybox do?" has the answer "Not
implement -t." (The option is in posix but not busybox...)

> This is *roughly* what procutils is doing, apart from that 'no need to
> special-case numbers' I'd assume.

Except "ps -t S0" is /dev/ttyS0...

> HTH,
> Isaac

Eh, I can work it out. It's just annoying.

Rob

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