linux-ext4 - Re: [PATCH 5/7] nonblocking aio: ext4

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Date:   Tue, 14 Feb 2017 12:52:17 -0700
From:   Andreas Dilger <adilger@...ger.ca>
To:     Goldwyn Rodrigues <rgoldwyn@...e.de>
Cc:     linux-fsdevel@...r.kernel.org, jack@...e.cz,
        Goldwyn Rodrigues <rgoldwyn@...e.com>,
        linux-ext4@...r.kernel.org
Subject: Re: [PATCH 5/7] nonblocking aio: ext4


> On Feb 13, 2017, at 7:46 PM, Goldwyn Rodrigues <rgoldwyn@...e.de> wrote:
> 
> From: Goldwyn Rodrigues <rgoldwyn@...e.com>
> 
> Return EAGAIN if any of the following checks fail for direct I/O:
> + i_rwsem is lockable
> + Writing beyond end of file (will trigger allocation)
> + Blocks are allocated at the write location
> 
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@...e.com>
> ---
> fs/ext4/file.c | 28 ++++++++++++++++++++++------
> 1 file changed, 22 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index 2a822d3..c8d1e41 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -93,11 +93,16 @@ ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
> {
> 	struct inode *inode = file_inode(iocb->ki_filp);
> 	int o_direct = iocb->ki_flags & IOCB_DIRECT;
> +	int nonblocking = iocb->ki_flags & IOCB_NONBLOCKING;
> 	int unaligned_aio = 0;
> 	int overwrite = 0;
> 	ssize_t ret;
> 
> -	inode_lock(inode);
> +	if (o_direct && nonblocking) {
> +		if (!inode_trylock(inode))
> +			return -EAGAIN;

Why do these all return -EAGAIN instead of -EWOULDBLOCK?  -EAGAIN is already
used in a number of places, and -EWOULDBLOCK seems more correct in the
"nonblocking" case?

> +	} else
> +		inode_lock(inode);

(style) "else" blocks should have braces when the "if" block has braces

> 	ret = generic_write_checks(iocb, from);
> 	if (ret <= 0)
> 		goto out;
> @@ -132,12 +137,18 @@ ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
> 	if (o_direct) {
> 		size_t length = iov_iter_count(from);
> 		loff_t pos = iocb->ki_pos;
> +		unsigned int blkbits = inode->i_blkbits;
> +
> +		if (nonblocking
> +			&& (pos + length > EXT4_BLOCK_ALIGN(i_size_read(inode), blkbits))) {

(style) "&&" should go at the end of the previous line
(style) continued lines should align after '(' on previous line
(style) no need for parenthesis around that comparison

> +			ret = -EAGAIN;
> +			goto out;
> +		}
> 
> 		/* check whether we do a DIO overwrite or not */
> -		if (ext4_should_dioread_nolock(inode) && !unaligned_aio &&
> -		    pos + length <= i_size_read(inode)) {
> +		if ((ext4_should_dioread_nolock(inode) && !unaligned_aio &&
> +			    pos + length <= i_size_read(inode)) || nonblocking) {

(style) continued line should align after second '(' of previous line

> 			struct ext4_map_blocks map;
> -			unsigned int blkbits = inode->i_blkbits;
> 			int err, len;
> 
> 			map.m_lblk = pos >> blkbits;
> @@ -157,8 +168,13 @@ ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
> 			 * non-flags are returned.  So we should check
> 			 * these two conditions.
> 			 */
> -			if (err == len && (map.m_flags & EXT4_MAP_MAPPED))
> -				overwrite = 1;
> +			if (err == len) {
> +			       if (map.m_flags & EXT4_MAP_MAPPED)
> +				       overwrite = 1;
> +			} else if (nonblocking) {
> +				ret = -EAGAIN;
> +				goto out;
> +			}
> 		}
> 	}
> 
> --
> 2.10.2
> 


Cheers, Andreas






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