linux-ext4 - Re: [PATCH v4 3/7] iomap: support direct I/O with fscrypt using blk-crypto

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Date:   Wed, 22 Jul 2020 16:26:25 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Dave Chinner <david@...morbit.com>
Cc:     Satya Tangirala <satyat@...gle.com>, linux-fscrypt@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, linux-ext4@...r.kernel.org,
        linux-xfs@...r.kernel.org
Subject: Re: [PATCH v4 3/7] iomap: support direct I/O with fscrypt using
 blk-crypto

On Wed, Jul 22, 2020 at 03:34:04PM -0700, Eric Biggers wrote:
> So, something like this:
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 44bad4bb8831..2816194db46c 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3437,6 +3437,15 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
>  	map.m_len = min_t(loff_t, (offset + length - 1) >> blkbits,
>  			  EXT4_MAX_LOGICAL_BLOCK) - map.m_lblk + 1;
>  
> +	/*
> +	 * When inline encryption is enabled, sometimes I/O to an encrypted file
> +	 * has to be broken up to guarantee DUN contiguity.  Handle this by
> +	 * limiting the length of the mapping returned.
> +	 */
> +	if (!(flags & IOMAP_REPORT))
> +		map.m_len = fscrypt_limit_io_blocks(inode, map.m_lblk,
> +						    map.m_len);
> +
>  	if (flags & IOMAP_WRITE)
>  		ret = ext4_iomap_alloc(inode, &map, flags);
>  	else
> 
> 
> That also avoids any confusion between pages and blocks, which is nice.

Correction: for fiemap, ext4 actually uses ext4_iomap_begin_report() instead of
ext4_iomap_begin().  So we don't need to check for !IOMAP_REPORT.

Also it could make sense to limit map.m_len after ext4_iomap_alloc() rather than
before, so that we don't limit the length of the extent that gets allocated but
rather just the length that gets returned to iomap.

- Eric