On Tue, Jul 18, 2017 at 04:21:07PM -0400, Joe Lawrence wrote: > On Mon, Jul 17, 2017 at 05:29:41PM +0200, Miroslav Benes wrote: > > > > On Wed, 28 Jun 2017, Joe Lawrence wrote: > > > > > +Brief API summary > > > +----------------- > > > + [ ... snip ...] > > > +* klp_shadow_detach() - detach and free all <*, num> shadow variables > > > + - find and remove any <*, num> references from hashtable > > > + - if found, release shadow variable > > > > I think that the second one should be klp_shadow_detach_all(), shouldn't > > it? > > Good catch, I'll fixup in v3. > > > > +static DEFINE_HASHTABLE(klp_shadow_hash, 12); > > > > Is there a reason, why you pick 12? I'm just curious. > > The hashtable bit-size was inherited from the kpatch implementation. > Perhaps Josh knows why this value was picked? My thinking was that it gives you about 4096 unique hash table entries for 32k of RAM. It was a rough guess. It's hard to really predict what size you need. > Aside: we could have per-livepatch hashtables if that was desired, this > value could be then adjusted accordingly. We haven't needed them for > kpatch, so I didn't see good reason to complicate things. I think a global hash table is much better because it allows you to deal more gracefully with patch upgrades. > > > + * > > > + * Note: allocates @new_size space for shadow variable data and copies > > > + * @new_size bytes from @new_data into the shadow varaible's own @new_data > > > + * space. If @new_data is NULL, @new_size is still allocated, but no > > > + * copy is performed. > > > > I must say I'm not entirely happy with this. I don't know if this is what > > Petr had in mind (I'm sure he'll get to the patch set soon). Calling > > memcpy instead of a simple assignment in v1 seems worse. > > This change was a bit of a experiment on my part in reaction to > adding klp_shadow_get_or_attach(). > > I like the simplicity of v1's pointer assignment -- in fact, moving all > allocation responsiblity (klp_shadow meta-data and data[] area) out to > the caller is doable, though implementing klp_shadow_get_or_attach() and > and klp_shadow_detach_all() complicates matters, for example, adding an > alloc/release callback. I originally attempted this for v2, but turned > back when the API and implementation grew complicated. If the memcpy > and gfp_flag restrictions are too ugly, I can try revisting that > approach. Ideas welcome :) Personally I'm not a fan of the callbacks, I like the v2 API. -- Josh -- To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
