[PATCH v4 40/68] cachefiles: Implement cache registration and withdrawal

[David Howells]

Jeff Layton <jlayton at kernel.org> wrote:

> > +	/* check parameters */
> > +	ret = -EOPNOTSUPP;
> > +	if (d_is_negative(root) ||
> > +	    !d_backing_inode(root)->i_op->lookup ||
> > +	    !d_backing_inode(root)->i_op->mkdir ||
> > +	    !(d_backing_inode(root)->i_opflags & IOP_XATTR) ||
> > +	    !root->d_sb->s_op->statfs ||
> > +	    !root->d_sb->s_op->sync_fs ||
> > +	    root->d_sb->s_blocksize > PAGE_SIZE)
> > +		goto error_unsupported;
> > +
> 
> That's quite a collection of tests.
> 
> Most are obvious, but some comments explaining the need for others would
> not be a bad thing. In particular, why is s_blocksize > PAGE_SIZE
> unsupported?

It can't do page-sized DIO requests to a filesystem with a block size larger
than a page.  In the future I can work around that in conjunction with
netfslib by expanding read and write sizes.

> Also, should you vet whether the fs supports i_op->tmpfile here ?

That's a good idea.

David