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SubjectRe: [PATCH 1/2] open: add close_range()
Date
Al Viro <viro@zeniv.linux.org.uk> wrote:

> Umm... That's going to be very painful if you dup2() something to MAX_INT and
> then run that; roughly 2G iterations of bouncing ->file_lock up and down,
> without anything that would yield CPU in process.
>
> If anything, I would suggest something like
>
> fd = *start_fd;
> grab the lock
> fdt = files_fdtable(files);
> more:
> look for the next eviction candidate in ->open_fds, starting at fd
> if there's none up to max_fd
> drop the lock
> return NULL
> *start_fd = fd + 1;
> if the fscker is really opened and not just reserved
> rcu_assign_pointer(fdt->fd[fd], NULL);
> __put_unused_fd(files, fd);
> drop the lock
> return the file we'd got
> if (unlikely(need_resched()))
> drop lock
> cond_resched();
> grab lock
> fdt = files_fdtable(files);
> goto more;
>
> with the main loop being basically
> while ((file = pick_next(files, &start_fd, max_fd)) != NULL)
> filp_close(file, files);

If we can live with close_from(int first) rather than close_range(), then this
can perhaps be done a lot more efficiently by:

new = alloc_fdtable(first);
spin_lock(&files->file_lock);
old = files_fdtable(files);
copy_fds(new, old, 0, first - 1);
rcu_assign_pointer(files->fdt, new);
spin_unlock(&files->file_lock);
clear_fds(old, 0, first - 1);
close_fdt_from(old, first);
kfree_rcu(old);

David

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