Re: [PATCH v5 2/2] mm: guestmem: Convert address_space operations to guestmem library

[Matthew Wilcox <willy@infradead.org>]

On Fri, Nov 22, 2024 at 09:29:39AM -0800, Elliot Berman wrote:
> A few near-term features are coming to guest_memfd which make sense to
> create a built-in library.

You haven't created a library, you've created a middle-layer.  This
file primarily consists of functions which redispatch to a function
pointer.  I think you'd be better off creating a library!  That is,
have the consumers register their own address_space_operations and
have functions in this library which provide useful implementations.

That's, eg, how iomap works:

const struct address_space_operations xfs_address_space_operations = {
        .read_folio             = xfs_vm_read_folio,
        .readahead              = xfs_vm_readahead,
        .writepages             = xfs_vm_writepages,
        .dirty_folio            = iomap_dirty_folio,
        .release_folio          = iomap_release_folio,
        .invalidate_folio       = iomap_invalidate_folio,
        .bmap                   = xfs_vm_bmap,
        .migrate_folio          = filemap_migrate_folio,
        .is_partially_uptodate  = iomap_is_partially_uptodate,
        .error_remove_folio     = generic_error_remove_folio,
        .swap_activate          = xfs_iomap_swapfile_activate,
};

Some of these functions are xfs specific, some are iomap specific and
some are the generic VFS implementations.