linux-ext4 - Re: [PATCH 2/8] nowait aio: Introduce RWF

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Date:   Thu, 11 May 2017 00:42:18 -0700
From:   Christoph Hellwig <hch@...radead.org>
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, willy@...radead.org,
        tom.leiming@...il.com, Goldwyn Rodrigues <rgoldwyn@...e.com>
Subject: Re: [PATCH 2/8] nowait aio: Introduce RWF_NOWAIT

On Tue, May 09, 2017 at 07:22:13AM -0500, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@...e.com>
> 
> This flag 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.
> 
> Unfortunately, aio_flags is not checked for validity, which would
> break existing applications which have it set to anything besides zero
> or IOCB_FLAG_RESFD. So, we are using aio_reserved1 and renaming it
> to aio_rw_flags.
> 
> 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.
> 
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@...e.com>
> ---
>  fs/9p/vfs_file.c        | 3 +++
>  fs/aio.c                | 6 ++++++
>  fs/ceph/file.c          | 3 +++
>  fs/cifs/file.c          | 3 +++
>  fs/fuse/file.c          | 3 +++
>  fs/nfs/direct.c         | 3 +++
>  fs/ocfs2/file.c         | 3 +++
>  include/linux/fs.h      | 5 ++++-
>  include/uapi/linux/fs.h | 1 +
>  mm/filemap.c            | 3 +++
>  10 files changed, 32 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/9p/vfs_file.c b/fs/9p/vfs_file.c
> index 3de3b4a89d89..403681db7723 100644
> --- a/fs/9p/vfs_file.c
> +++ b/fs/9p/vfs_file.c
> @@ -411,6 +411,9 @@ v9fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
>  	loff_t origin;
>  	int err = 0;
>  
> +	if (iocb->ki_flags & IOCB_NOWAIT)
> +		return -EOPNOTSUPP;
> +
>  	retval = generic_write_checks(iocb, from);
>  	if (retval <= 0)
>  		return retval;
> diff --git a/fs/aio.c b/fs/aio.c
> index 020fa0045e3c..ea9f8581d902 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)) {

Weird indentation.  Either align after the opening if brace:

	if ((req->common.ki_flags & IOCB_NOWAIT) &&
	    !(req->common.ki_flags & IOCB_DIRECT)) {

or using two tabs:

	if ((req->common.ki_flags & IOCB_NOWAIT) &&
			!(req->common.ki_flags & IOCB_DIRECT)) {

if the first version looks confusing, but never using the same
indentation level as the following code.

Except for that the patch looks fine to me:

Reviewed-by: Christoph Hellwig <hch@....de>