Re: [PATCH 1/3] fs, xfs: introduce S_IOMAP_IMMUTABLE

From	Colin Walters <walters@verbum.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH 1/3] fs, xfs: introduce S_IOMAP_IMMUTABLE
Date	2017-08-01 04:20 +0200
Message-ID	<u9uWS-5OL-9@gated-at.bofh.it> (permalink)
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On Mon, Jul 31, 2017, at 02:23 PM, Darrick J. Wong wrote:

> I don't think F_SEAL_{SHRINK,GROW} prevents reflinking or CoW of file data,
> which are two things that cannot happen under S_IOMAP_IMMUTABLE that
> aren't size changes.  From the implementation it looks like shrink and
> grow are only supposed to disallow changes to i_size, not i_blocks (or
> the file block map).

True. 

> Then again, I suppose F_SEAL_* only work on shmem, so maybe it simply
> isn't defined for any other filesystem...?  e.g. it doesn't prohibit
> reflink, but the only fs implementing seals doesn't support reflink.
> 
> <shrug>
> 
> Seals cannot be removed, which is too strict for the S_IOMAP_IMMUTABLE
> user cases being presented.

To be clear, the set of use cases is swap files and DAX, right?  Or is there anything else?
I can't imagine why anyone would want to turn a swap file back into a regular file.
I haven't fully followed DAX, but I'd take your word for it if people want to
be able to remove the flag after.

Anyways, I think your broader point is right; the use cases are different enough
that it doesn't make sense to try to add S_CONTENT_IMMUTABLE (or however 
one decides to call it) at the same time.

Thread

Re: [PATCH 1/3] fs, xfs: introduce S_IOMAP_IMMUTABLE Colin Walters <walters@verbum.org> - 2017-07-31 18:10 +0200
  Re: [PATCH 1/3] fs, xfs: introduce S_IOMAP_IMMUTABLE Colin Walters <walters@verbum.org> - 2017-07-31 18:40 +0200
    Re: [PATCH 1/3] fs, xfs: introduce S_IOMAP_IMMUTABLE Colin Walters <walters@verbum.org> - 2017-07-31 19:50 +0200
      Re: [PATCH 1/3] fs, xfs: introduce S_IOMAP_IMMUTABLE "Darrick J. Wong" <darrick.wong@oracle.com> - 2017-07-31 20:30 +0200
        Re: [PATCH 1/3] fs, xfs: introduce S_IOMAP_IMMUTABLE Colin Walters <walters@verbum.org> - 2017-08-01 04:20 +0200
          Re: [PATCH 1/3] fs, xfs: introduce S_IOMAP_IMMUTABLE Dave Chinner <david@fromorbit.com> - 2017-08-01 04:50 +0200
            Re: [PATCH 1/3] fs, xfs: introduce S_IOMAP_IMMUTABLE Christoph Hellwig <hch@lst.de> - 2017-08-05 11:50 +0200
  Re: [PATCH 1/3] fs, xfs: introduce S_IOMAP_IMMUTABLE Dan Williams <dan.j.williams@intel.com> - 2017-07-31 18:40 +0200

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