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

From: Eric Biggers <ebiggers@kernel.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Satya Tangirala <satyat@google.com>,
	linux-fscrypt@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-f2fs-devel@lists.sourceforge.net,
	linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org
Subject: Re: [PATCH v4 3/7] iomap: support direct I/O with fscrypt using blk-crypto
Date: Wed, 22 Jul 2020 16:26:25 -0700	[thread overview]
Message-ID: <20200722232625.GB83434@sol.localdomain> (raw)
In-Reply-To: <20200722223404.GA76479@sol.localdomain>

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