linux-kernel - Re: [PATCH v2 2/5] fs, xfs: introduce FALLOC_FL_SEAL_BLOCK

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Date:   Fri, 4 Aug 2017 16:43:50 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Dave Chinner <david@...morbit.com>
Cc:     "Darrick J. Wong" <darrick.wong@...cle.com>,
        Jan Kara <jack@...e.cz>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-xfs@...r.kernel.org, Jeff Moyer <jmoyer@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andy Lutomirski <luto@...nel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2 2/5] fs, xfs: introduce FALLOC_FL_SEAL_BLOCK_MAP

On Fri, Aug 4, 2017 at 4:31 PM, Dave Chinner <david@...morbit.com> 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.