[bug] renice not POSIX compliant

[bug] renice not POSIX compliant

[Stephane Chazelas]

Hi, there are a few POSIX compliance issues with the "renice"
command from util-linux.

First and more importantly, per POSIX, like for "nice", "-n"
is meant to take an "increment"/"adjustment", not an absolute
value.

As in

renice -n 5 "$pid"

is meant to increase the nice value by 5. While the traditional,
BSD-style:

renice 5 "$pid"

sets its absolute value to 5.

util-linux added "-n" in 2009 for POSIX compliance (see
https://git.kernel.org/pub/scm/utils/util-linux/util-linux.git/commit/?id=7cfbafda9c484a8cadefc47ee115086e803d9391),
but the "-n" is just ignored. Since 2010, the --help message
does say that -n/--priority takes an "increment"
(https://git.kernel.org/pub/scm/utils/util-linux/util-linux.git/commit/?id=296351b0f112c821bffbe8ce7aa35d716251051d)
but that's not what happens in practice (it still sets the
niceness to the value specified).

$ nice -n 1 sh -c 'renice -n 2 "$$"; ps -o nice,comm -p "$$"; exit'
29606 (process ID) old priority 1, new priority 2
 NI COMMAND
  2 sh


Also, a POSIX renice utility is meant to parse the options the
usual (getopt(3)) way. In particular,

renice -gn 1 -- 123

Is meant to increase the niceness of pgid 123 by 1, but fails in
util-linux renice.

$ renice -gn 1 -- "$$"
renice: invalid priorty '-gn'
Try 'renice --help' for more information.

-p, -g, -u are meant to specify how *all* operands are to be
interpreted, they are not options that take arguments.

renice +1 123
renice +1 123 -u me

are unspecified by POSIX, so it's fine for util-linux to handle
the BSD way, but

renice -n 1 -u me -p 123

Is meant to increase the niceness of users "me", "-p" and "123".

Also, calling it "--priority" is quite misleading as the
niceness is rather the opposite of priority. GNU "nice" uses
"--adjustment" as the long-option equivalent of "-n" (note that
FreeBSD also calls it "priority" though)..

IMO, the best way to handle it would be to do a BSD-style
parsing when the first argument matches the [-+]?\d+ RE, and do
a POSIX getopt_long parsing otherwise with:

Change the (POSIX style) options to:

  -n/--adjustment <num>: niceness increment
  -v/--value (deprecated: --priority) <num>: exact niceness value
  -g/--pgrp (no arg): interpret operands as gids.
  -u/--user (no arg): interpret operands as user names/ids
  -p/-pid (no arg): interpret operands as pids.
  --help/--version...

And keep the

renice niceness [[-p/--pid] pid ...] [[-g/--pgrp] pgid ...] [[-u/--user] user ...]

usage for backward compatibility and BSD compatibility.

Note that there's currently a bug in the latest version of the
POSIX specification in that it says that positive increments
should *decrease* the niceness
(http://austingroupbugs.net/view.php?id=1286).

See
https://unix.stackexchange.com/questions/541673/how-do-i-start-a-shell-the-way-all-the-processes-ran-from-within-it-and-processe/541691#541691
for more details.

-- 
Stephane

Re: [bug] renice not POSIX compliant

[Karel Zak]

 Hi,

(sorry for delay)

On Sat, Sep 14, 2019 at 02:55:37PM +0100, Stephane Chazelas wrote:
> util-linux added "-n" in 2009 for POSIX compliance (see
> https://git.kernel.org/pub/scm/utils/util-linux/util-linux.git/commit/?id=7cfbafda9c484a8cadefc47ee115086e803d9391),
> but the "-n" is just ignored. Since 2010, the --help message
> does say that -n/--priority takes an "increment"
> (https://git.kernel.org/pub/scm/utils/util-linux/util-linux.git/commit/?id=296351b0f112c821bffbe8ce7aa35d716251051d)
> but that's not what happens in practice (it still sets the
> niceness to the value specified).

I have fixed the --help and removed "increment".

> Also, a POSIX renice utility is meant to parse the options the
> usual (getopt(3)) way. In particular,
> 
> renice -gn 1 -- 123
> 
> Is meant to increase the niceness of pgid 123 by 1, but fails in
> util-linux renice.
> 
> $ renice -gn 1 -- "$$"
> renice: invalid priorty '-gn'
> Try 'renice --help' for more information.
> 
> -p, -g, -u are meant to specify how *all* operands are to be
> interpreted, they are not options that take arguments.

well, this is --help stupidity, man page is better. Fixed.

> renice +1 123
> renice +1 123 -u me
> 
> are unspecified by POSIX, so it's fine for util-linux to handle
> the BSD way, but
> 
> renice -n 1 -u me -p 123
> 
> Is meant to increase the niceness of users "me", "-p" and "123".
> 
> Also, calling it "--priority" is quite misleading as the
> niceness is rather the opposite of priority. GNU "nice" uses
> "--adjustment" as the long-option equivalent of "-n" (note that
> FreeBSD also calls it "priority" though)..
> 
> IMO, the best way to handle it would be to do a BSD-style
> parsing when the first argument matches the [-+]?\d+ RE, and do
> a POSIX getopt_long parsing otherwise with:

hmm... but it will introduce regression as -n is interpreted as
absolute number now, no increment. And at first glance at Google you
can see that -n is in almost all how-to articles ;-(

I think we need to keep -n in the game for BSD-style too.

> Change the (POSIX style) options to:
> 
>   -n/--adjustment <num>: niceness increment

>   -v/--value (deprecated: --priority) <num>: exact niceness value
>   -g/--pgrp (no arg): interpret operands as gids.
>   -u/--user (no arg): interpret operands as user names/ids
>   -p/-pid (no arg): interpret operands as pids.
>   --help/--version...
> 
> And keep the
> 
> renice niceness [[-p/--pid] pid ...] [[-g/--pgrp] pgid ...] [[-u/--user] user ...]
> 
> usage for backward compatibility and BSD compatibility.

What about:

  renice [-n] [+-]<prio> [[-p/--pid] pid ...] [[-g/--pgrp] pgid ...] [[-u/--user] user ...]

and keep <prio> is absolute number if without +/-; and as relative
if prefixed with + or - ?

It means people who use 

  renice -n 10 [-p ... -g ... -u ... ]

will not see any regression, and people who use

  renice -n +2 [-p ... -g ... -u ... ]

will see that it work as expected :-)


For POSIX-like getopt_long() way, how does it support more arguments?
For example in BSD way you can use:

    renice 10 -p 1 -p 2 -p 3

to apply 10 for processes 1, 2 and 3. How you can write it in POSIX way?

    Karel

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