Re: [PATCH 3/17] afs: convert afs_dir_get_page to read_kmap_page

[David Howells <dhowells@redhat.com>]

Nate Diller <nate.diller@gmail.com> wrote:

> but that's a lot of code to avoid a single stack allocation.  The
> whole fake file pointer thing still strikes me as a little ugly, and
> you're definitely not the first one who needed this sort of hackery.
> ugh

A better way might be to stick a void * in struct file and pass that through
to readpage() and readpages() instead of the struct file *.  That way, anyone
who wants the traditional arrangement can just point that extra void * at the
struct file.

Of course, I'm in favour of making it a struct key * like this:

	struct address_space_operations {
	...
		int (*readpage)(struct key *, struct page *);
	...
		int (*readpages)(struct key *, struct address_space *,
				struct list_head *, unsigned);
	...
	};

	struct file {
	...
		struct key *f_key;
	};

	struct page *filemap_nopage(struct vm_area_struct *area, ...)
	{
	...
		struct file *file = area->vm_file;
	...
		error = mapping->a_ops->readpage(file->f_key, page);
	...
	}
	
But I'm not sure the NFS crew, for instance, would be happy with that.  Maybe
passing file->private_data through would do.  That's basically what NFS and
FUSE, for instance, want, and it would also do for AFS.

David