On Mon, Sep 18, 2017 at 2:31 AM, Jan Kara [off-list ref] wrote:

On Sun 17-09-17 19:39:45, Christoph Hellwig wrote:

quoted

On Sat, Sep 16, 2017 at 08:44:14PM -0700, Dan Williams wrote:

quoted

So it wasn't all that easy, and Linus declined to take it. I think we
should add a new ->mmap_validate() file operation and save the
tree-wide cleanup until later.

Note that we already have a mmap_capabilities callout for nommu,
I wonder if we could generalize that.

So if I understood Dan right, Linus refused to merge the patch which adds
'flags' argument to ->mmap callback. That is actually logically independent
change from validating flags passed to mmap(2) syscall. Dan did it just to
save himself from adding a VMA flag for MAP_DIRECT.

For validating flags passed to mmap(2), I agree we could use
->mmap_capabilities() instead of mmap_supported_mask Dan has added. But I
don't have a strong opinion there.

The drawback I see with mmap_capabilities is that it requires all mmap
flags to have a corresponding vm_flag. After the cold reaction the
VM_DAX flag received I'd want to be sure they were on board with this
direction.

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