Re: [PATCH 3/4] fs: expose LOOKUP_NONBLOCK through openat2() RESOLVE_NONBLOCK

[Al Viro <viro@zeniv.linux.org.uk>]

On Mon, Dec 14, 2020 at 12:13:23PM -0700, Jens Axboe wrote:
> Now that we support non-blocking path resolution internally, expose it
> via openat2() in the struct open_how ->resolve flags. This allows
> applications using openat2() to limit path resolution to the extent that
> it is already cached.
> 
> If the lookup cannot be satisfied in a non-blocking manner, openat2(2)
> will return -1/-EAGAIN.
> 
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
>  fs/open.c                    | 6 ++++++
>  include/linux/fcntl.h        | 2 +-
>  include/uapi/linux/openat2.h | 4 ++++
>  3 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/open.c b/fs/open.c
> index 9af548fb841b..a83434cfe01c 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -1087,6 +1087,12 @@ inline int build_open_flags(const struct open_how *how, struct open_flags *op)
>  		lookup_flags |= LOOKUP_BENEATH;
>  	if (how->resolve & RESOLVE_IN_ROOT)
>  		lookup_flags |= LOOKUP_IN_ROOT;
> +	if (how->resolve & RESOLVE_NONBLOCK) {
> +		/* Don't bother even trying for create/truncate open */
> +		if (flags & (O_TRUNC | O_CREAT))
> +			return -EAGAIN;

Why not O_TMPFILE here as well?