Re: [PATCH] btrfs-progs: add dev stats returncode option

["Austin S. Hemmelgarn" <ahferroin7@gmail.com>]

On 2016-12-01 15:32, Mike Fleetwood wrote:
> On 1 December 2016 at 18:43, Austin S. Hemmelgarn <ahferroin7@gmail.com> wrote:
>> Currently, `btrfs device stats` returns non-zero only when there was an
>> error getting the counter values.  This is fine for when it gets run by a
>> user directly, but is a serious pain when trying to use it in a script or
>> for monitoring since you need to parse the (not at all machine friendly)
>> output to check the counter values.
>>
>> This patch adds an option ('-s') which causes `btrfs device stats`
>> to set bit 7 in the return code if any of the counters are non-zero.
>> This greatly simplifies checking from a script or monitoring software
>> if any errors have been recorded.  In the event that this switch is
>> passed and an error occurs reading the stats, the return code will have
>> bit 0 set (so if there are errors reading counters, and the counters
>> which were read were non-zero, the return value will be 129).
>
> I don't think using bit 7 is a good idea.  Bash (and I think all
> shells) report exist status 128+SIGNUM when the process is killed by a
> signal.  I.e. status 129 would be returned when a process is killed by
> SIGHUP.
>
> Perhaps bit 6 would be OK to use.
Ah, you're right, I actually completely forgot about this.  I'll send an 
updated version later today.
>
> Thanks,
> Mike
>
> https://tiswww.case.edu/php/chet/bash/bashref.html#Exit-Status
> "Exit statuses fall between 0 and 255, though, as explained below, the
> shell may use values above 125 specially. ...
>
> When a command terminates on a fatal signal whose number is N, Bash
> uses the value 128+N as the exit status. ...
>
> If a command is not found, the child process created to execute it
> returns a status of 127. If a command is found but is not executable,
> the return status is 126."