Re: [PATCH liburing] man/io_uring_enter.2: add notes about direct open/accept

[Jens Axboe <axboe@kernel.dk>]

On 8/31/21 1:52 PM, Pavel Begunkov wrote:
> Add a few lines describing openat/openat2/accept bypassing normal file
> tables and installing files right into the fixed file table.
> 
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>  man/io_uring_enter.2 | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> diff --git a/man/io_uring_enter.2 b/man/io_uring_enter.2
> index 9ccedef..52a5e13 100644
> --- a/man/io_uring_enter.2
> +++ b/man/io_uring_enter.2
> @@ -511,6 +511,18 @@ field. See also
>  .BR accept4(2)
>  for the general description of the related system call. Available since 5.5.
>  
> +If the
> +.I file_index
> +field is set to a non-negative number, the file won't be installed into the
> +normal file table as usual but will be placed into the fixed file table at index
> +.I file_index - 1.
> +In this case, instead of returning a file descriptor, the result will contain
> +0 on success or an error. If there is already a file registered at this index,

I don't think non-negative is correct, it has to be set to a positive
number. non-negative would include 0, which isn't correct.

Should also include a note on if these types of file are used, they
won't work in anything but io_uring. That's obvious to us, but should be
noted that they then only live within the realm of the ring itself, not
the system as a whole.

-- 
Jens Axboe