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

Oleg Nesterov
2019-05-22T16:57:37Z

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;
}

?

Then close_range() can do

while (fd < max_fd)
fd = close_next_fd(fd, maxfd);

Oleg.