Re: [Xenomai-core] [patch 2/4] RTDM support for select-like service.

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

Jan Kiszka wrote:
 > Gilles Chanteperdrix wrote:
 > > Would not it be simpler to put a pointer to the task_struct ? After all,
 > > it already has a pid, comm and mm, and a file descriptor will not
 > > survive a task_struct thanks to automatic closing of file descriptors.
 > 
 > Hmm, hmm, hmmmm... Sounds reasonable, should be safe.

Actually no, we can not do that because a task_struct may well disappear
and the rtdm_process continue to exist as long as another thread uses the
same mm.

 > 
 > > 
 > >  Could you
 > >  > live without the check until we have per-process fd tabled, or was it
 > >  > essential for the select thing?
 > > 
 > > An application which I ported to Xenomai (and which uses the select
 > > call) closes all file descriptors in a for loop. The purpose of this
 > > loop is, I guess, to avoid leaving a file descriptor opened that was
 > > passed through exec.
 > 
 > OK.
 > 
 > So, will you change rtdm_process too? Thanks.

I commited the select support, without any change to rtdm_context_get or
rtdm_process. So, now, how do you prefer this to be fixed, by adding an
mm struct to the rtdm_process struct ? By the way, after thinking about
it I can live without this fix: I just have to stop the loop closing
file descriptors at 768, so that it will not try to close RTDM file
descriptors.

While commiting the support for select, I also had a dependency problem
in Kconfig: when support for posix select is enabled the posix module
uses a function defined in the RTDM module. So, there is one invalid
configuration: posix built-in with support for select and rtdm built as
a module. I could not find a way to express this condition in the
Kconfig language, so I just made a comment depend on this condition, but
would be happy if anyone found a better solution.

-- 


					    Gilles Chanteperdrix.