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Date:   Wed, 24 May 2017 09:49:58 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
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,
        axboe@...nel.dk, linux-api@...r.kernel.org,
        adam.manzanares@....com, viro@...iv.linux.org.uk,
        Goldwyn Rodrigues <rgoldwyn@...e.com>
Subject: Re: [PATCH 09/10] xfs: nowait aio support

On Wed, May 24, 2017 at 11:41:49AM -0500, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@...e.com>
> 
> If IOCB_NOWAIT is set, bail if the i_rwsem is not lockable
> immediately.
> 
> IF IOMAP_NOWAIT is set, return EAGAIN in xfs_file_iomap_begin
> if it needs allocation either due to file extension, writing to a hole,
> or COW or waiting for other DIOs to finish.
> 
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@...e.com>
> Reviewed-by: Christoph Hellwig <hch@....de>

Looks good,
Reviewed-by: Darrick J. Wong <darrick.wong@...cle.com>

--D

> ---
>  fs/xfs/xfs_file.c  | 19 ++++++++++++++-----
>  fs/xfs/xfs_iomap.c | 17 +++++++++++++++++
>  2 files changed, 31 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 35703a801372..b307940e7d56 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -541,8 +541,11 @@ xfs_file_dio_aio_write(
>  		iolock = XFS_IOLOCK_SHARED;
>  	}
>  
> -	xfs_ilock(ip, iolock);
> -
> +	if (!xfs_ilock_nowait(ip, iolock)) {
> +		if (iocb->ki_flags & IOCB_NOWAIT)
> +			return -EAGAIN;
> +		xfs_ilock(ip, iolock);
> +	}
>  	ret = xfs_file_aio_write_checks(iocb, from, &iolock);
>  	if (ret)
>  		goto out;
> @@ -553,9 +556,15 @@ xfs_file_dio_aio_write(
>  	 * otherwise demote the lock if we had to take the exclusive lock
>  	 * for other reasons in xfs_file_aio_write_checks.
>  	 */
> -	if (unaligned_io)
> -		inode_dio_wait(inode);
> -	else if (iolock == XFS_IOLOCK_EXCL) {
> +	if (unaligned_io) {
> +		/* If we are going to wait for other DIO to finish, bail */
> +		if (iocb->ki_flags & IOCB_NOWAIT) {
> +			if (atomic_read(&inode->i_dio_count))
> +				return -EAGAIN;
> +		} else {
> +			inode_dio_wait(inode);
> +		}
> +	} else if (iolock == XFS_IOLOCK_EXCL) {
>  		xfs_ilock_demote(ip, XFS_IOLOCK_EXCL);
>  		iolock = XFS_IOLOCK_SHARED;
>  	}
> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> index 94e5bdf7304c..8b0e3c1e086d 100644
> --- a/fs/xfs/xfs_iomap.c
> +++ b/fs/xfs/xfs_iomap.c
> @@ -1016,6 +1016,15 @@ xfs_file_iomap_begin(
>  
>  	if ((flags & (IOMAP_WRITE | IOMAP_ZERO)) && xfs_is_reflink_inode(ip)) {
>  		if (flags & IOMAP_DIRECT) {
> +			/*
> +			 * A reflinked inode will result in CoW alloc.
> +			 * FIXME: It could still overwrite on unshared extents
> +			 * and not need allocation.
> +			 */
> +			if (flags & IOMAP_NOWAIT) {
> +				error = -EAGAIN;
> +				goto out_unlock;
> +			}
>  			/* may drop and re-acquire the ilock */
>  			error = xfs_reflink_allocate_cow(ip, &imap, &shared,
>  					&lockmode);
> @@ -1033,6 +1042,14 @@ xfs_file_iomap_begin(
>  
>  	if ((flags & IOMAP_WRITE) && imap_needs_alloc(inode, &imap, nimaps)) {
>  		/*
> +		 * If nowait is set bail since we are going to make
> +		 * allocations.
> +		 */
> +		if (flags & IOMAP_NOWAIT) {
> +			error = -EAGAIN;
> +			goto out_unlock;
> +		}
> +		/*
>  		 * We cap the maximum length we map here to MAX_WRITEBACK_PAGES
>  		 * pages to keep the chunks of work done where somewhat symmetric
>  		 * with the work writeback does. This is a completely arbitrary
> -- 
> 2.12.0
> 
> --
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