Re: [PATCH 2.6.27-rc5] Allow set RLIMIT_NOFILE to RLIM_INFINITY

[Adam Tkac <vonsch@gmail.com>]

On Wed, Sep 10, 2008 at 02:31:41PM -0700, Andrew Morton wrote:
> On Tue, 9 Sep 2008 09:14:07 +0200
> Adam Tkac <vonsch@gmail.com> wrote:
> 
> > when process wants set limit of open files to RLIM_INFINITY it gets
> > EPERM even if it has CAP_SYS_RESOURCE capability. Attached patch
> > should fix the problem. Please add me to CC of your responses because
> > I'm not member of list.
> > 
> > Regards, Adam
> > 
> > -- 
> > Adam Tkac
> > 
> > 
> > [linux26-openfiles.patch  text/plain (634B)]
> > --- a/kernel/sys.c
> > +++ b/kernel/sys.c
> > @@ -1458,8 +1458,14 @@ asmlinkage long sys_setrlimit(unsigned i
> >  	if ((new_rlim.rlim_max > old_rlim->rlim_max) &&
> >  	    !capable(CAP_SYS_RESOURCE))
> >  		return -EPERM;
> > -	if (resource == RLIMIT_NOFILE && new_rlim.rlim_max > sysctl_nr_open)
> > -		return -EPERM;
> > +	if (resource == RLIMIT_NOFILE) {
> > +		if (new_rlim.rlim_max == RLIM_INFINITY)
> > +			new_rlim.rlim_max = sysctl_nr_open;
> > +		if (new_rlim.rlim_cur == RLIM_INFINITY)
> > +			new_rlim.rlim_cur = sysctl_nr_open;
> > +		if (new_rlim.rlim_max > sysctl_nr_open)
> > +			return -EPERM;
> > +	}
> 
> The kernel has had this behaviour for a long time.  2.6.13 had:
> 
> 	if ((new_rlim.rlim_max > old_rlim->rlim_max) &&
> 	    !capable(CAP_SYS_RESOURCE))
> 		return -EPERM;
> 	if (resource == RLIMIT_NOFILE && new_rlim.rlim_max > NR_OPEN)
> 			return -EPERM;
> 
> I don't immediately see a problem with your change, but what makes you
> believe that it is needed?  Is there some standard which we're
> violating?  Is there some operational situation in which the current
> behaviour is causing a problem?
> 
> Thanks.

Well, this change is not _absolutely_ needed because everyone who wants
unlimited file descriptors he could set it to NR_OPEN. Look on
example (from BIND):

...
#elif defined(NR_OPEN) && defined(__linux__)
        /*
         * Some Linux kernels don't accept RLIM_INFINIT; the maximum
         * possible value is the NR_OPEN defined in linux/fs.h.
         */
        if (resource == isc_resource_openfiles && rlim_value == RLIM_INFINITY) {
                rl.rlim_cur = rl.rlim_max = NR_OPEN;
                unixresult = setrlimit(unixresource, &rl);
                if (unixresult == 0)
                        return (ISC_R_SUCCESS);
        }
#elif ...

I think that when you allow set RLIMIT_NOFILE to RLIM_INFINITY you
increase portability - you don't have to check if OS is linux and then
use different schema for limits.

Regards, Adam

-- 
Adam Tkac