Re: [PATCH 3/3] fs: support RWF_NOWAIT for buffered reads

[Goldwyn Rodrigues <rgoldwyn@suse.de>]

On 06/29/2017 04:25 PM, Christoph Hellwig wrote:
> This is based on the old idea and code from Milosz Tanski.  With the
> aio nowait code it becomes mostly trivial now.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/aio.c           |  6 ------
>  fs/btrfs/file.c    |  2 +-
>  fs/ext4/file.c     |  6 +++---
>  fs/xfs/xfs_file.c  | 11 +++++++++--
>  include/linux/fs.h |  6 +++---
>  5 files changed, 16 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/aio.c b/fs/aio.c
> index dcad3a66748c..d93daa076726 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -1593,12 +1593,6 @@ 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");
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index 59e2dccdf75b..f82dad241b39 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -3088,7 +3088,7 @@ static loff_t btrfs_file_llseek(struct file *file, loff_t offset, int whence)
>  
>  static int btrfs_file_open(struct inode *inode, struct file *filp)
>  {
> -	filp->f_mode |= FMODE_AIO_NOWAIT;
> +	filp->f_mode |= FMODE_NOWAIT;
>  	return generic_file_open(inode, filp);
>  }
>  

We should modify the NOWAIT check in btrfs_file_write_iter() to return
-EAGAIN for buffered writes.


> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index 58e2eeaa0bc4..5330ea99681a 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -223,6 +223,8 @@ ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
>  	if (IS_DAX(inode))
>  		return ext4_dax_write_iter(iocb, from);
>  #endif
> +	if (!o_direct && (iocb->ki_flags & IOCB_NOWAIT))
> +		return -EAGAIN;
>  
>  	if (!inode_trylock(inode)) {
>  		if (iocb->ki_flags & IOCB_NOWAIT)
> @@ -455,9 +457,7 @@ static int ext4_file_open(struct inode * inode, struct file * filp)
>  			return ret;
>  	}
>  
> -	/* Set the flags to support nowait AIO */
> -	filp->f_mode |= FMODE_AIO_NOWAIT;
> -
> +	filp->f_mode |= FMODE_NOWAIT;
>  	return dquot_file_open(inode, filp);
>  }
>  
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 17f27a2fb5e2..1068f0b01090 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -259,7 +259,11 @@ xfs_file_buffered_aio_read(
>  
>  	trace_xfs_file_buffered_read(ip, iov_iter_count(to), iocb->ki_pos);
>  
> -	xfs_ilock(ip, XFS_IOLOCK_SHARED);
> +	if (!xfs_ilock_nowait(ip, XFS_IOLOCK_SHARED)) {
> +		if (iocb->ki_flags & IOCB_NOWAIT)
> +			return -EAGAIN;
> +		xfs_ilock(ip, XFS_IOLOCK_SHARED);
> +	}
>  	ret = generic_file_read_iter(iocb, to);
>  	xfs_iunlock(ip, XFS_IOLOCK_SHARED);
>  
> @@ -636,6 +640,9 @@ xfs_file_buffered_aio_write(
>  	int			enospc = 0;
>  	int			iolock;
>  
> +	if (iocb->ki_flags & IOCB_NOWAIT)
> +		return -EAGAIN;
> +
>  write_retry:
>  	iolock = XFS_IOLOCK_EXCL;
>  	xfs_ilock(ip, iolock);
> @@ -911,7 +918,7 @@ xfs_file_open(
>  		return -EFBIG;
>  	if (XFS_FORCED_SHUTDOWN(XFS_M(inode->i_sb)))
>  		return -EIO;
> -	file->f_mode |= FMODE_AIO_NOWAIT;
> +	file->f_mode |= FMODE_NOWAIT;
>  	return 0;
>  }
>  
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 65adbddb3163..a78834bedb61 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -144,8 +144,8 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
>  /* File was opened by fanotify and shouldn't generate fanotify events */
>  #define FMODE_NONOTIFY		((__force fmode_t)0x4000000)
>  
> -/* File is capable of returning -EAGAIN if AIO will block */
> -#define FMODE_AIO_NOWAIT	((__force fmode_t)0x8000000)
> +/* File is capable of returning -EAGAIN if I/O will block */
> +#define FMODE_NOWAIT	((__force fmode_t)0x8000000)
>  
>  /*
>   * Flag for rw_copy_check_uvector and compat_rw_copy_check_uvector
> @@ -3092,7 +3092,7 @@ static inline int kiocb_set_rw_flags(struct kiocb *ki, int flags)
>  		return -EOPNOTSUPP;
>  
>  	if (flags & RWF_NOWAIT) {
> -		if (!(ki->ki_filp->f_mode & FMODE_AIO_NOWAIT))
> +		if (!(ki->ki_filp->f_mode & FMODE_NOWAIT))
>  			return -EOPNOTSUPP;
>  		ki->ki_flags |= IOCB_NOWAIT;
>  	}
> 

-- 
Goldwyn