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SubjectRe: [PATCH] nextfd(2)
On Sun, Apr 01, 2012 at 05:43:25PM +0200, Eric Dumazet wrote:
> On Sun, 2012-04-01 at 15:57 +0300, Alexey Dobriyan wrote:
>
> > +
> > +/* Return first opened file descriptor which is >= than the argument. */
> > +SYSCALL_DEFINE1(nextfd, unsigned int, fd)
> > +{
> > + struct files_struct *files = current->files;
> > + struct fdtable *fdt;
> > +
> > + rcu_read_lock();
> > + fdt = files_fdtable(files);
> > + while (fd < fdt->max_fds) {
> > + struct file *file;
> > +
> > + file = rcu_dereference_check_fdtable(files, fdt->fd[fd]);
> > + if (file) {
> > + rcu_read_unlock();
> > + return fd;
> > + }
> > + fd++;
> > + }
> > + rcu_read_unlock();
> > + return -ESRCH;
> > +}
>
> Interesting idea but what about using fdt->open_fds bitmap to have a
> fast search and less cache pollution ?
>
> alloc_fd(start, flags) uses find_next_zero_bit(), you could use
> find_next_bit().

Indeed.
I've copied code from /proc/*/fd implementation which does loop.

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