On Wed, Mar 23, 2022 at 9:08 AM Benjamin Tissoires
<benjamin.tissoires@xxxxxxxxxx> wrote:
>
> Hi Alexei,
>
> On Tue, Mar 22, 2022 at 11:51 PM Alexei Starovoitov
> <alexei.starovoitov@xxxxxxxxx> wrote:
> >
> > On Fri, Mar 18, 2022 at 9:16 AM Benjamin Tissoires
> > <benjamin.tissoires@xxxxxxxxxx> wrote:
> > >
> > > +u8 *hid_bpf_report_fixup(struct hid_device *hdev, u8 *rdesc, unsigned int *size)
> > > +{
> > > + int ret;
> > > + struct hid_bpf_ctx_kern ctx = {
> > > + .type = HID_BPF_RDESC_FIXUP,
> > > + .hdev = hdev,
> > > + .size = *size,
> > > + };
> > > +
> > > + if (bpf_hid_link_empty(&hdev->bpf, BPF_HID_ATTACH_RDESC_FIXUP))
> > > + goto ignore_bpf;
> > > +
> > > + ctx.data = kmemdup(rdesc, HID_MAX_DESCRIPTOR_SIZE, GFP_KERNEL);
> > > + if (!ctx.data)
> > > + goto ignore_bpf;
> > > +
> > > + ctx.allocated_size = HID_MAX_DESCRIPTOR_SIZE;
> > > +
> > > + ret = hid_bpf_run_progs(hdev, &ctx);
> > > + if (ret)
> > > + goto ignore_bpf;
> > > +
> > > + if (ctx.size > ctx.allocated_size)
> > > + goto ignore_bpf;
> > > +
> > > + *size = ctx.size;
> > > +
> > > + if (*size) {
> > > + rdesc = krealloc(ctx.data, *size, GFP_KERNEL);
> > > + } else {
> > > + rdesc = NULL;
> > > + kfree(ctx.data);
> > > + }
> > > +
> > > + return rdesc;
> > > +
> > > + ignore_bpf:
> > > + kfree(ctx.data);
> > > + return kmemdup(rdesc, *size, GFP_KERNEL);
> > > +}
> > > +
> > > int __init hid_bpf_module_init(void)
> > > {
> > > struct bpf_hid_hooks hooks = {
> > > .hdev_from_fd = hid_bpf_fd_to_hdev,
> > > .pre_link_attach = hid_bpf_pre_link_attach,
> > > + .post_link_attach = hid_bpf_post_link_attach,
> > > .array_detach = hid_bpf_array_detach,
> > > };
> > >
> > > diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
> > > index 937fab7eb9c6..3182c39db006 100644
> > > --- a/drivers/hid/hid-core.c
> > > +++ b/drivers/hid/hid-core.c
> > > @@ -1213,7 +1213,8 @@ int hid_open_report(struct hid_device *device)
> > > return -ENODEV;
> > > size = device->dev_rsize;
> > >
> > > - buf = kmemdup(start, size, GFP_KERNEL);
> > > + /* hid_bpf_report_fixup() ensures we work on a copy of rdesc */
> > > + buf = hid_bpf_report_fixup(device, start, &size);
> >
> > Looking at this patch and the majority of other patches...
> > the code is doing a lot of work to connect HID side with bpf.
> > At the same time the evolution of the patch series suggests
> > that these hook points are not quite stable. More hooks and
> > helpers are being added.
> > It tells us that it's way too early to introduce a stable
> > interface between HID and bpf.
>
> I understand that you might be under the impression that the interface
> is changing a lot, but this is mostly due to my poor knowledge of all
> the arcanes of eBPF.
> The overall way HID-BPF works is to work on a single array, and we
> should pretty much be sorted out. There are a couple of helpers to be
> able to communicate with the device, but the API has been stable in
> the kernel for those for quite some time now.
>
> The variations in the hooks is mostly because I don't know what is the
> best representation we can use in eBPF for those, and the review
> process is changing that.
I think such a big feature as this one, especially that most BPF folks
are (probably) not familiar with the HID subsystem in the kernel,
would benefit from a bit of live discussion during BPF office hours.
Do you think you can give a short overview of what you are trying to
achieve with some background context on HID specifics at one of the
next BPF office hours? We have a meeting scheduled every week on
Thursday, 9am Pacific time. But people need to put their topic onto
the agenda, otherwise the meeting is cancelled. See [0] for
spreadsheet and links to Zoom meeting, agenda, etc.
[0] https://docs.google.com/spreadsheets/d/1LfrDXZ9-fdhvPEp_LHkxAMYyxxpwBXjywWa0AejEveU
[...]
