On Thu 11-05-17 14:17:04, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
>
> RWF_NOWAIT informs kernel to bail out if an AIO request will block
> for reasons such as file allocations, or a writeback triggered,
> or would block while allocating requests while performing
> direct I/O.
>
> RWF_NOWAIT is translated to IOCB_NOWAIT for iocb->ki_flags.
>
> The check for -EOPNOTSUPP is placed in generic_file_write_iter(). This
> is called by most filesystems, either through fsops.write_iter() or through
> the function defined by write_iter(). If not, we perform the check defined
> by .write_iter() which is called for direct IO specifically.
>
> Filesystems xfs, btrfs and ext4 would be supported in the following patches.
...
> diff --git a/fs/aio.c b/fs/aio.c
> index 020fa0045e3c..34027b67e2f4 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -1592,6 +1592,12 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
> goto out_put_req;
> }
>
> + if ((req->common.ki_flags & IOCB_NOWAIT) &&
> + !(req->common.ki_flags & IOCB_DIRECT)) {
> + ret = -EOPNOTSUPP;
> + goto out_put_req;
> + }
> +
> ret = put_user(KIOCB_KEY, &user_iocb->aio_key);
> if (unlikely(ret)) {
> pr_debug("EFAULT: aio_key\n");
I think you need to also check here that the IO is write. So that NOWAIT
reads don't silently pass.
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
