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

[Al Viro]

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.

s/HUGETLBFS/HUGEPAGES/, please.

> While cleaning things up, change the name of is_file_hugepages() to
> is_file_hugetlbfs().  The term hugepages is a bit ambiguous.

Don't, especially since the very next patch adds such on overlayfs...

Incidentally, can a hugetlbfs be a lower layer, while the upper one
is a normal filesystem?  What should happen on copyup?