support for limit of open file descriptors for a child process

support for limit of open file descriptors for a child process

[Ram Gupta]

Hi,
    I came across a problem regarding the issue of number of open
file descriptors.The scenario is as below.
 I have a controlling process which launches other different
apllication including third party ones. It also enforces various
resource limits including number of open file descriptors. This
process forks & reads the resource limits from a configuration files,
applies the resource limits & then execs for the corresponding
application. The process has its own various number of open file
descriptors. If the limit of open file descriptor for the child
application is less than the number of file descriptors  of the parent
process, then the child application file can not be opened & exec
fails in this case.

I searched solution for this problem but could not find an existing
way to solve it. I thought of couple of ways to do it. One idea is to
create another flag for clone which makes it not to inherit the open
file descriptors & use clone with that flag instead of fork .The other
approach is to create a new system call & parent process can call that
system call before calling the setrlimit.

I am looking for your opinion about the better way . Further if it is helpful
 then I can submit the patch also.

Thanks in advance
regards
Ram Gupta

Re: support for limit of open file descriptors for a child process

[Bernd Petrovitsch]

On Thu, 2006-09-14 at 10:21 -0500, Ram Gupta wrote:
> Hi,
>     I came across a problem regarding the issue of number of open
> file descriptors.The scenario is as below.
>  I have a controlling process which launches other different
> apllication including third party ones. It also enforces various
> resource limits including number of open file descriptors. This
> process forks & reads the resource limits from a configuration files,
> applies the resource limits & then execs for the corresponding
> application. The process has its own various number of open file
> descriptors. If the limit of open file descriptor for the child
> application is less than the number of file descriptors  of the parent
> process, then the child application file can not be opened & exec
> fails in this case.
> 
> I searched solution for this problem but could not find an existing
> way to solve it. I thought of couple of ways to do it. One idea is to

-) simply close(2) the superfluous file descriptors unconditionally
   before exec(2)ing the child process 
-) set the close-on-exec flag via fcntl(2) on these file descriptors
   after opening them

	Bernd
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