Re: [PATCH 1/3] ext4: Add alignment check for DAX mount
On 05/01/2016 08:31 PM, Christoph Hellwig wrote:
On Fri, Apr 29, 2016 at 02:39:33PM -0600, Toshi Kani wrote:
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 304c712..90a8670 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3421,6 +3421,12 @@ static int ext4_fill_super(struct super_block *sb, void *data,
int silent)
> "error: unsupported blocksize for dax");
> goto failed_mount;
> }
> + if (sb->s_bdev->bd_part->start_sect % (PAGE_SIZE / 512) ||
> + sb->s_bdev->bd_part->nr_sects % (PAGE_SIZE / 512)) {
> + ext4_msg(sb, KERN_ERR,
> + "error: unaligned partition for dax");
> + goto failed_mount;
> + }
> if (!sb->s_bdev->bd_disk->fops->direct_access) {
> ext4_msg(sb, KERN_ERR,
> "error: device does not support dax");
Factor your new checks and the ->direct_access into a new helper. It
should take the block device as file systems might have multiple
underlying devices.
This already exists as part of bdev_direct_access()
All the code needs to do is call bdev_direct_access() on sector ZERO and
see if it is successful. If the alignment is broken it will fail.
Infact the FS does not even need the second if (!...bd_disk->fops->direct_access)
check either because it is also done inside bdev_direct_access(). The only check
needed is calling bdev_direct_access() and the generic layer does all the
checks needed already.
Cheers
Boaz