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

Eric Biggers
2020-07-22T23:26:29Z

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