Re: [PATCH v4 1/2] hugetlb: use f_mode & FMODE_HUGETLBFS to identify hugetlbfs files

[Matthew Wilcox]

On Thu, Jun 11, 2020 at 05:46:43PM -0700, Mike Kravetz wrote:
> The routine is_file_hugepages() checks f_op == hugetlbfs_file_operations
> to determine if the file resides in hugetlbfs.  This is problematic when
> the file is on a union or overlay.  Instead, define a new file mode
> FMODE_HUGETLBFS which is set when a hugetlbfs file is opened.  The mode
> can easily be copied to other 'files' derived from the original hugetlbfs
> file.
> 
> With this change hugetlbfs_file_operations can be static as it should be.
> 
> There is also a (duplicate) set of shm file operations used for the routine
> is_file_shm_hugepages().  Instead of setting/using special f_op's, just
> propagate the FMODE_HUGETLBFS mode.  This means is_file_shm_hugepages() and
> the duplicate f_ops can be removed.
> 
> While cleaning things up, change the name of is_file_hugepages() to
> is_file_hugetlbfs().  The term hugepages is a bit ambiguous.

I was going to have objections to this before I read it more carefully
and realised that the "shm" here is sysvipc and doesn't have anything
to do with the huge page support in shmfs.

> A subsequent patch will propagate FMODE_HUGETLBFS in overlayfs.
> 
> Suggested-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>

Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>

I might have suggested splitting the rename of is_file_hugetlbfs() from
the rest of this patch, but I wouldn't resend to change that.