Re: [PATCH v1 1/2] open: add close_range()

Christian Brauner
2019-05-23T14:14:48Z

On Thu, May 23, 2019 at 01:51:18PM +0200, Christian Brauner wrote:
> On Wed, May 22, 2019 at 06:57:37PM +0200, Oleg Nesterov wrote:
> > On 05/22, Christian Brauner wrote:
> > >
> > > +static struct file *pick_file(struct files_struct *files, unsigned fd)
> > > {
> > > - struct file *file;
> > > + struct file *file = NULL;
> > > struct fdtable *fdt;
> > >
> > > spin_lock(&files->file_lock);
> > > @@ -632,15 +629,65 @@ int __close_fd(struct files_struct *files, unsigned fd)
> > > goto out_unlock;
> > > rcu_assign_pointer(fdt->fd[fd], NULL);
> > > __put_unused_fd(files, fd);
> > > - spin_unlock(&files->file_lock);
> > > - return filp_close(file, files);
> > >
> > > out_unlock:
> > > spin_unlock(&files->file_lock);
> > > - return -EBADF;
> > > + return file;
> >
> > ...
> >
> > > +int __close_range(struct files_struct *files, unsigned fd, unsigned max_fd)
> > > +{
> > > + unsigned int cur_max;
> > > +
> > > + if (fd > max_fd)
> > > + return -EINVAL;
> > > +
> > > + rcu_read_lock();
> > > + cur_max = files_fdtable(files)->max_fds;
> > > + rcu_read_unlock();
> > > +
> > > + /* cap to last valid index into fdtable */
> > > + if (max_fd >= cur_max)
> > > + max_fd = cur_max - 1;
> > > +
> > > + while (fd <= max_fd) {
> > > + struct file *file;
> > > +
> > > + file = pick_file(files, fd++);
> >
> > Well, how about something like
> >
> > static unsigned int find_next_opened_fd(struct fdtable *fdt, unsigned start)
> > {
> > unsigned int maxfd = fdt->max_fds;
> > unsigned int maxbit = maxfd / BITS_PER_LONG;
> > unsigned int bitbit = start / BITS_PER_LONG;
> >
> > bitbit = find_next_bit(fdt->full_fds_bits, maxbit, bitbit) * BITS_PER_LONG;
> > if (bitbit > maxfd)
> > return maxfd;
> > if (bitbit > start)
> > start = bitbit;
> > return find_next_bit(fdt->open_fds, maxfd, start);
> > }
>
> >
> > unsigned close_next_fd(struct files_struct *files, unsigned start, unsigned maxfd)
> > {
> > unsigned fd;
> > struct file *file;
> > struct fdtable *fdt;
> >
> > spin_lock(&files->file_lock);
> > fdt = files_fdtable(files);
> > fd = find_next_opened_fd(fdt, start);
> > if (fd >= fdt->max_fds || fd > maxfd) {
> > fd = -1;
> > goto out;
> > }
> >
> > file = fdt->fd[fd];
> > rcu_assign_pointer(fdt->fd[fd], NULL);
> > __put_unused_fd(files, fd);
> > out:
> > spin_unlock(&files->file_lock);
> >
> > if (fd = -1u)
> > return fd;
> >
> > filp_close(file, files);
> > return fd + 1;
> > }
>
> Thanks, Oleg!
>
> I kept it dumb and was about to reply that your solution introduces more
> code when it seemed we wanted to keep this very simple for now.
> But then I saw that find_next_opened_fd() already exists as
> find_next_fd(). So it's actually not bad compared to what I sent in v1.
> So - with some small tweaks (need to test it and all now) - how do we
> feel about?:

That's obviously not correct atm but I'll send out a tweaked version in
a bit.

Christian