Re: [PATCH v2 2/5] fs, xfs: introduce FALLOC_FL_SEAL_BLOCK_MAP

[Dan Williams]

On Fri, Aug 4, 2017 at 4:31 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
> On Thu, Aug 03, 2017 at 07:28:17PM -0700, Dan Williams wrote:
>> diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
>> index fe0f8f7f4bb7..46d8eb9e19fc 100644
>> --- a/fs/xfs/xfs_bmap_util.c
>> +++ b/fs/xfs/xfs_bmap_util.c
>> @@ -1393,6 +1393,107 @@ xfs_zero_file_space(
>>
>>  }
>>
>> +/* Return 1 if hole detected, 0 if not, and < 0 if fail to determine */
>> +STATIC int
>> +xfs_file_has_holes(
>> +     struct xfs_inode        *ip)
>> +{
>
> Why do we need this function?
>
> We've just run xfs_alloc_file_space() across the entire range we
> are sealing, so we've already guaranteed that it won't have holes
> in it.

I'm sure this is due to my ignorance of the scope of XFS_IOLOCK_EXCL
vs XFS_ILOCK_EXCL. I had assumed that since we drop and retake
XFS_ILOCK_EXCL that we need to re-validate the block map before
setting S_IOMAP_IMMUTABLE.