On Mon, Sep 15, 2025 at 09:42:59AM -0300, Jason Gunthorpe wrote:
> On Mon, Sep 15, 2025 at 01:23:30PM +0100, Lorenzo Stoakes wrote:
> > On Mon, Sep 15, 2025 at 09:11:12AM -0300, Jason Gunthorpe wrote:
> > > On Wed, Sep 10, 2025 at 09:22:03PM +0100, Lorenzo Stoakes wrote:
> > > > +static inline void mmap_action_remap(struct mmap_action *action,
> > > > + unsigned long addr, unsigned long pfn, unsigned long
> > > > size,
> > > > + pgprot_t pgprot)
> > > > +{
> > > > + action->type = MMAP_REMAP_PFN;
> > > > +
> > > > + action->remap.addr = addr;
> > > > + action->remap.pfn = pfn;
> > > > + action->remap.size = size;
> > > > + action->remap.pgprot = pgprot;
> > > > +}
> > >
> > > These helpers drivers are supposed to call really should have kdocs.
> > >
> > > Especially since 'addr' is sort of ambigous.
> >
> > OK.
> >
> > >
> > > And I'm wondering why they don't take in the vm_area_desc? Eg shouldn't
> > > we be strongly discouraging using anything other than
> > > vma->vm_page_prot as the last argument?
> >
> > I need to abstract desc from action so custom handlers can perform
> > sub-actions. It's unfortunate but there we go.
>
> Why? I don't see this as required
>
> Just mark the functions as manipulating the action using the 'action'
> in the fuction name.
Because now sub-callers that partially map using one method and partially map
using another now need to have a desc too that they have to 'just know' which
fields to update or artificially set up.
The vmcore case does something like this.
Instead, we have actions where it's 100% clear what's going to happen.
>
> > > I'd probably also have a small helper wrapper for the very common case
> > > of whole vma:
> > >
> > > /* Fill the entire VMA with pfns starting at pfn. Caller must have
> > > * already checked desc has an appropriate size */
> > > mmap_action_remap_full(struct vm_area_desc *desc, unsigned long pfn)
> >
> > See above re: desc vs. action.
>
> Yet, this is the API most places actually want.
>
> > It'd be hard to know how to get the context right that'd need to be
> > supplied to
> > the callback.
> >
> > In kcov's case it'd be kcov->area + an offset.
>
> Just use pgoff
>
> > So we'd need an offset parameter, the struct file *, whatever else to be
> > passed.
>
> Yes
>
> > And then we'll find a driver where that doesn't work and we're screwed.
>
> Bah, you keep saying that but we also may never even find one.
OK let me try something like this, then. I guess I can update it later if
we discover such a dirver.
>
> Jason
Cheers, Lorenzo
