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
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