Re: [PATCH 2/6] iomap: move bdev and dax_dev in a union

Darrick J. Wong
2018-06-19T06:25:57Z

On Thu, Jun 14, 2018 at 02:04:53PM +0200, Christoph Hellwig wrote:
> We always either ask for a block device or DAX device mapping, so we can
> use the same space for both.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> fs/ext2/inode.c | 6 ++++--
> fs/ext4/inode.c | 6 ++++--
> fs/xfs/xfs_iomap.c | 6 ++++--
> include/linux/iomap.h | 6 ++++--
> 4 files changed, 16 insertions(+), 8 deletions(-)
>
> diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
> index 71635909df3b..8aead4e9dbc1 100644
> --- a/fs/ext2/inode.c
> +++ b/fs/ext2/inode.c
> @@ -815,9 +815,11 @@ static int ext2_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
> return ret;
>
> iomap->flags = 0;
> - iomap->bdev = inode->i_sb->s_bdev;
> iomap->offset = (u64)first_block << blkbits;
> - iomap->dax_dev = sbi->s_daxdev;
> + if (IS_DAX(inode))
> + iomap->dax_dev = sbi->s_daxdev;
> + else
> + iomap->bdev = inode->i_sb->s_bdev;
>
> if (ret == 0) {
> iomap->type = IOMAP_HOLE;
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 2ea07efbe016..79027e99118f 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3524,8 +3524,10 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
> iomap->flags = 0;
> if (ext4_inode_datasync_dirty(inode))
> iomap->flags |= IOMAP_F_DIRTY;
> - iomap->bdev = inode->i_sb->s_bdev;
> - iomap->dax_dev = sbi->s_daxdev;
> + if (IS_DAX(inode))
> + iomap->dax_dev = sbi->s_daxdev;
> + else
> + iomap->bdev = inode->i_sb->s_bdev;
> iomap->offset = (u64)first_block << blkbits;
> iomap->length = (u64)map.m_len << blkbits;
>
> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> index c6ce6f9335b6..c9c3d0df5e4c 100644
> --- a/fs/xfs/xfs_iomap.c
> +++ b/fs/xfs/xfs_iomap.c
> @@ -70,8 +70,10 @@ xfs_bmbt_to_iomap(
> }
> iomap->offset = XFS_FSB_TO_B(mp, imap->br_startoff);
> iomap->length = XFS_FSB_TO_B(mp, imap->br_blockcount);
> - iomap->bdev = xfs_find_bdev_for_inode(VFS_I(ip));
> - iomap->dax_dev = xfs_find_daxdev_for_inode(VFS_I(ip));
> + if (IS_DAX(VFS_I(ip)))
> + iomap->dax_dev = xfs_find_daxdev_for_inode(VFS_I(ip));
> + else
> + iomap->bdev = xfs_find_bdev_for_inode(VFS_I(ip));
> }
>
> xfs_extlen_t
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index a044a824da85..212f4d59bcbf 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -53,8 +53,10 @@ struct iomap {
> u64 length; /* length of mapping, bytes */
> u16 type; /* type of mapping */
> u16 flags; /* flags for mapping */
> - struct block_device *bdev; /* block device for I/O */
> - struct dax_device *dax_dev; /* dax_dev for dax operations */
> + union {
> + struct block_device *bdev;
> + struct dax_device *dax_dev;

Is this going to blow up iomap_dax_zero? It seems to use both bdev and
dax_dev on __dax_zero_page_range, which definitely uses both.

(Or did all that get rearranged when I wasn't looking?)

Also, I guess this will break iomap swapfiles since it checks
iomap->bdev which we stop supplying with this patch...
though I have no idea if DAX swapfiles are even supported.

What's the harm in supplying both pointers?

--D

> + };
> };
>
> /*
> --
> 2.17.1
>
> --
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