linux-ext4 - Re: [PATCH v2 4/6] ext4: reorder map.m_flags checks in ext4_iomap

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Message-Id: <20190909083040.8126B4204B@d06av24.portsmouth.uk.ibm.com>
Date:   Mon, 9 Sep 2019 14:00:39 +0530
From:   Ritesh Harjani <riteshh@...ux.ibm.com>
To:     Matthew Bobrowski <mbobrowski@...browski.org>, tytso@....edu,
        jack@...e.cz, adilger.kernel@...ger.ca
Cc:     linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        david@...morbit.com, hch@...radead.org, darrick.wong@...cle.com
Subject: Re: [PATCH v2 4/6] ext4: reorder map.m_flags checks in
 ext4_iomap_begin()



On 9/9/19 4:49 AM, Matthew Bobrowski wrote:
> For iomap direct IO write code path changes, we need to accommodate
> for the case where the block mapping flags passed to ext4_map_blocks()
> will result in m_flags having both EXT4_MAP_MAPPED and
> EXT4_MAP_UNWRITTEN bits set. In order for the allocated unwritten
> extents to be converted properly in the end_io handler, iomap->type
> must be set to IOMAP_UNWRITTEN, so we need to reshuffle the
> conditional statement in order to achieve this.
> 
> This change is a no-op for DAX code path as the block mapping flag
> passed to ext4_map_blocks() when IS_DAX(inode) never results in
> EXT4_MAP_MAPPED and EXT4_MAP_UNWRITTEN being set at once.
> 
> Signed-off-by: Matthew Bobrowski <mbobrowski@...browski.org>

Looks good to me.

Reviewed-by: Ritesh Harjani <riteshh@...ux.ibm.com>


> ---
>   fs/ext4/inode.c | 17 ++++++++++++++---
>   1 file changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 761ce6286b05..efb184928e51 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3581,10 +3581,21 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
>   		iomap->type = delalloc ? IOMAP_DELALLOC : IOMAP_HOLE;
>   		iomap->addr = IOMAP_NULL_ADDR;
>   	} else {
> -		if (map.m_flags & EXT4_MAP_MAPPED) {
> -			iomap->type = IOMAP_MAPPED;
> -		} else if (map.m_flags & EXT4_MAP_UNWRITTEN) {
> +		/*
> +		 * Flags passed to ext4_map_blocks() for direct IO
> +		 * writes can result in m_flags having both
> +		 * EXT4_MAP_MAPPED and EXT4_MAP_UNWRITTEN bits set. In
> +		 * order for allocated unwritten extents to be
> +		 * converted to written extents in the end_io handler
> +		 * correctly, we need to ensure that the iomap->type
> +		 * is also set appropriately in that case. Thus, we
> +		 * need to check whether EXT4_MAP_UNWRITTEN is set
> +		 * first.
> +		 */
> +		if (map.m_flags & EXT4_MAP_UNWRITTEN) {
>   			iomap->type = IOMAP_UNWRITTEN;
> +		} else if (map.m_flags & EXT4_MAP_MAPPED) {
> +			iomap->type = IOMAP_MAPPED;
>   		} else {
>   			WARN_ON_ONCE(1);
>   			return -EIO;
>