Question about exec_string()

[Erwan Velu <erwan@enovance.com>]

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