Re: modutils (Re: cipe 1.2.0 & kernel 2.2.x)
Richard Gooch (rgooch@atnf.csiro.au)
Fri, 26 Mar 1999 07:43:11 +1100
Malcolm Beattie writes:
> Olaf Titz writes:
> > I assume this is just this code in ciped:
> > for (i=getdtablesize()-1; i>2; --i)
> > (void) close(i);
> > which makes sure all fds are closed (and deliberately ignores the
> > errors). Are your 1000 really 253 or do you use an -ac kernel with
> > higher fd limit? :-)
> >
> > This "close everything but standard fds" is employed by a number of
> > programs, among them shells and perl, to avoid fd leakage. It is
> > harmless.
>
> On our heavily loaded Digital UNIX Alphaserver (which defaults to 4096
> file descriptors per process), each "close everything but standard fds"
> hits the system with another 4093 syscalls. When that's done frequently
> (up to a few logins per second) it becomes a significant fraction of
> the syscalls/sec which seems to correlate fairly well with the whole
> system's performance.
>
> Since Linux is now entering the realms of plenty of file descriptors,
> I wonder if it's worth having a closefdset() syscall used as follows:
>
> fd_set most;
> FD_ZERO(&most);
> for (i=getdtablesize()-1; i>2; --i)
> FD_SET(i, &most);
> closefdset(&most);
>
> On the positive side, it reduces all those extra syscalls at a stroke
> and it's simple to write. On the negative side, it's a non-standard
> interface and could easily be considered a unnecessary wart. It also
> can't return any errors beyond "at least one close failed" but that
> doesn't matter for the purposes it would be used for.
If you really want to do this, use a poll(2)-like interface
instead. poll(2) is more scalable than select(2) and a structure like
struct follfd could return status information about each FD.
Regards,
Richard....
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