Re: [RFC PATCH v1 4/9] uaccess: Introduce copy_{to/from}_user_partial()

Geert Uytterhoeven <[email protected]> Tue, 28 Apr 2026 11:25:11 +0200
Newsgroups gmane.comp.freedesktop.xorg.drivers.intel,gmane.linux.ports.alpha,gmane.linux.kernel,gmane.linux.kernel.arc,gmane.linux.ports.arm.kernel,gmane.linux.ports.mips,gmane.linux.ports.ppc64.devel,gmane.comp.emulators.kvm.devel,gmane.linux.ports.riscv,gmane.linux.ports.sparc,gmane.linux.uml.devel,gmane.linux.kernel.efi,gmane.comp.freedesktop.amd-gfx,gmane.comp.video.dri.devel,gmane.linux.network,gmane.linux.kernel.wireless.general,gmane.linux.kernel.spi.devel,gmane.linux.drivers.video-input-infrastructure,gmane.linux.serial,gmane.linux.usb.general,gmane.comp.emulators.xen.devel,gmane.linux.file-systems,gmane.linux.kernel.bpf,gmane.linux.kernel.mm,gmane.linux.x25,gmane.linux.kernel.rust,gmane.linux.sound,gmane.linux.ports.hexagon,gmane.linux.ports.parisc,gmane.linux.ports.sh.devel,gmane.linux.kernel.cross-arch
Message-ID <CAMuHMdUvTBWoDN_wUo2n8-gkoheJ+-rbwew53OvoAwo8G5n1qg@mail.gmail.com> 
Hi Christophe,

Thanks for your patch!

On Mon, 27 Apr 2026 at 19:18, Christophe Leroy (CS GROUP)
<[email protected]> wrote:
> Today there are approximately 3000 calls for copy_to_user() and
> 3000 calls to copy_from_user().
>
> The majority of callers of copy_{to/from}_user() don't care about the
> return value, they only check whether it is 0 or not, and when it is
> not 0 they handle it as a -EACCES.

I think the "a" can be dropped.

> In order to allow better optimisation of copy_{to/from}_user() when
> the size of the copy is known at build time, create new fonctions

functions

> named copy_{to/from}_user_partial() to be used by the few callers
> that are interested in partial copies and need to now how many

know

> bytes remain at the end of the copy.
>
> For the time being it is just the same as copy_{to/from}_user().
>
> Signed-off-by: Christophe Leroy (CS GROUP) <[email protected]>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds