Question about exec_string()

Question about exec_string()

[Erwan Velu]

Hi,

I'm continuing my experiments with fio and adding features to genfio.
I'm currently adding to genfio the exec_{pre|post}run support.

I'm benching some ceph and so need to reset OSD's caches with echoing in 
drop_cache.
To achieve that, I'm using kash (from kanif) and having the following 
syntaxt :

kash -n m1sw1 -n m1sw2 -n m1sw3 -n m2sw1 -n m2sw3 -- echo 3 > 
/proc/sys/vm/drop_caches

To be able to ssh all this nodes, I need my env to be kept as it relies 
on my ssh-agent.
That's where I do my troubles.

exec_prerun uses exec_string() with does a "sh -c %s'". That does loose 
my env and prevents me from executing my command.

I've been testing by removing the "sh -c" and only keep "%s" which works 
perfectly.
I'm so wondering what was the targeted role of executing sh instead of 
running the command directly.
If you agree about this change, I can provide the patch.

Note also it would be lovely to have an explicit redirection of the 
output as unless it's pretty hard to understand if the command got run 
with its associated output.

Cheers,
Erwan

Re: Question about exec_string()

[Jens Axboe]

On Tue, Jul 16 2013, Erwan Velu wrote:
> Hi,
> 
> I'm continuing my experiments with fio and adding features to genfio.
> I'm currently adding to genfio the exec_{pre|post}run support.
> 
> I'm benching some ceph and so need to reset OSD's caches with echoing in
> drop_cache.
> To achieve that, I'm using kash (from kanif) and having the following
> syntaxt :
> 
> kash -n m1sw1 -n m1sw2 -n m1sw3 -n m2sw1 -n m2sw3 -- echo 3 >
> /proc/sys/vm/drop_caches
> 
> To be able to ssh all this nodes, I need my env to be kept as it relies on
> my ssh-agent.
> That's where I do my troubles.
> 
> exec_prerun uses exec_string() with does a "sh -c %s'". That does loose my
> env and prevents me from executing my command.
> 
> I've been testing by removing the "sh -c" and only keep "%s" which works
> perfectly.
> I'm so wondering what was the targeted role of executing sh instead of
> running the command directly.
> If you agree about this change, I can provide the patch.

I suspect that would be fine.

> Note also it would be lovely to have an explicit redirection of the output
> as unless it's pretty hard to understand if the command got run with its
> associated output.

I'll happily take a patch to include the output into the general logging
:-). That's the way it should work.

-- 
Jens Axboe

Re: Question about exec_string()

[Erwan Velu]

On 16/07/2013 22:58, Jens Axboe wrote:
>
> I'll happily take a patch to include the output into the general logging
> :-). That's the way it should work.
That could be very verbose. Isn't that a problem ?
I though to split it to let user read it later if needed instead of 
flooding the current console.

Re: Question about exec_string()

[Jens Axboe]

On Tue, Jul 16 2013, Erwan Velu wrote:
> On 16/07/2013 22:58, Jens Axboe wrote:
> >
> >I'll happily take a patch to include the output into the general logging
> >:-). That's the way it should work.
> That could be very verbose. Isn't that a problem ?
> I though to split it to let user read it later if needed instead of flooding
> the current console.

Sure, that'd be fine too. You could have jobname-prerun.txt etc created.
I'm fine with either approach.

-- 
Jens Axboe