Messages in this thread | | | Date | Wed, 09 Aug 2023 20:08:30 +0200 | From | Takashi Iwai <> | Subject | Re: [PATCH RFC] Introduce uniptr_t as a generic "universal" pointer |
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On Wed, 09 Aug 2023 19:01:50 +0200, Linus Torvalds wrote: > > On Wed, 9 Aug 2023 at 09:05, Takashi Iwai <tiwai@suse.de> wrote: > > > > OTOH, it simplifies the code well for us; as of now, we have two > > callbacks for copying PCM memory from/to the device, distinct for > > kernel and user pointers. It's basically either copy_from_user() or > > memcpy() of the given size depending on the caller. The sockptr_t or > > its variant would allow us to unify those to a single callback. > > I didn't see the follow-up patches that use this, but... > > > (And yeah, iov_iter is there, but it's definitely overkill for the > > purpose.) > > You can actually use a "simplified form" of iov_iter, and it's not all that bad. > > If the actual copying operation is just a memcpy, you're all set: just > do copy_to/from_iter(), and it's a really nice interface, and you > don't have to carry "ptr+size" things around. > > And we now have a simple way to generate simple iov_iter's, so > *creating* the iter is trivial too: > > struct iov_iter iter; > int ret = import_ubuf(ITER_SRC/DEST, uptr, len, &iter); > > if (unlikely(ret < 0)) > return ret; > > and you're all done. You can now pass '&iter' around, and it has a > nice user pointer and a range in it, and copying that thing is easy. > > Perhaps somewhat strangely (*) we don't have the same for a simple > kernel buffer, but adding that wouldn't be hard. You either end up > using a 'kvec', or we could even add something like ITER_KBUF if it > really matters. > > Right now the kernel buffer init is a *bit* more involved than the > above ubuf case: > > struct iov_iter iter; > struct kvec kvec = { kptr, len}; > > iov_iter_kvec(&iter, ITER_SRC/DEST, &kvec, 1, len); > > and that's maybe a *bit* annoying, but we could maybe simplify this > with some helper macros even without ITER_KBUF. > > So yes, iov_iter does have some abstraction overhead, but it really > isn't that bad. And it *does* allow you to do a lot of things, and can > actually simplify the users quite a bit, exactly because it allows you > to just pass that single iter pointer around, and you automatically > have not just the user/kernel distinction, you have the buffer size, > and you have a lot of helper functions to use it. > > I really think that if you want a user-or-kernel buffer interface, you > should use these things. > > Please? At least look into it.
All sounds convincing, I'll take a look tomorrow. Thanks!
Takashi
> > Linus > > (*) Well, not so strange - we've just never needed it. >
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