On 18/02/2021 12:27, Lennert Buytenhek wrote:
> IORING_OP_GETDENTS behaves much like getdents64(2) and takes the same
> arguments, but with a small twist: it takes an additional offset
> argument, and reading from the specified directory starts at the given
> offset.
>
> For the first IORING_OP_GETDENTS call on a directory, the offset
> parameter can be set to zero, and for subsequent calls, it can be
> set to the ->d_off field of the last struct linux_dirent64 returned
> by the previous IORING_OP_GETDENTS call.
>
> Internally, if necessary, IORING_OP_GETDENTS will vfs_llseek() to
> the right directory position before calling vfs_getdents().
>
> IORING_OP_GETDENTS may or may not update the specified directory's
> file offset, and the file offset should not be relied upon having
> any particular value during or after an IORING_OP_GETDENTS call.
>
> Signed-off-by: Lennert Buytenhek <buytenh@xxxxxxxxxxxxxx>
> ---
> fs/io_uring.c | 73 +++++++++++++++++++++++++++++++++++
> include/uapi/linux/io_uring.h | 1 +
> 2 files changed, 74 insertions(+)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 056bd4c90ade..6853bf48369a 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -635,6 +635,13 @@ struct io_mkdir {
> struct filename *filename;
> };
>
[...]
> +static int io_getdents(struct io_kiocb *req, unsigned int issue_flags)
> +{
> + struct io_getdents *getdents = &req->getdents;
> + bool pos_unlock = false;
> + int ret = 0;
> +
> + /* getdents always requires a blocking context */
> + if (issue_flags & IO_URING_F_NONBLOCK)
> + return -EAGAIN;
> +
> + /* for vfs_llseek and to serialize ->iterate_shared() on this file */
> + if (file_count(req->file) > 1) {
Looks racy, is it safe? E.g. can be concurrently dupped and used, or just
several similar IORING_OP_GETDENTS requests.
> + pos_unlock = true;
> + mutex_lock(&req->file->f_pos_lock);
> + }
> +
> + if (req->file->f_pos != getdents->pos) {
> + loff_t res = vfs_llseek(req->file, getdents->pos, SEEK_SET);
I may be missing the previous discussions, but can this ever become
stateless, like passing an offset? Including readdir.c and beyond.
> + if (res < 0)
> + ret = res;
> + }
> +
> + if (ret == 0) {
> + ret = vfs_getdents(req->file, getdents->dirent,
> + getdents->count);
> + }
> +
> + if (pos_unlock)
> + mutex_unlock(&req->file->f_pos_lock);
> +
> + if (ret < 0) {
> + if (ret == -ERESTARTSYS)
> + ret = -EINTR;
> + req_set_fail_links(req);
> + }
> + io_req_complete(req, ret);
> + return 0;
> +}
[...]
--
Pavel Begunkov
