linux-ext4 - Re: [PATCH 04/10] fs: Introduce RWF

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Date:   Mon, 15 May 2017 11:47:09 +0200
From:   Jan Kara <jack@...e.cz>
To:     Goldwyn Rodrigues <rgoldwyn@...e.de>
Cc:     linux-fsdevel@...r.kernel.org, jack@...e.com, hch@...radead.org,
        linux-block@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        sagi@...mberg.me, avi@...lladb.com, axboe@...nel.dk,
        linux-api@...r.kernel.org, Goldwyn Rodrigues <rgoldwyn@...e.com>
Subject: Re: [PATCH 04/10] fs: Introduce RWF_NOWAIT

On Thu 11-05-17 14:17:04, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@...e.com>
> 
> 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@...e.com>
SUSE Labs, CR