On Fri, Jan 13, 2023 at 10:09:32AM +0100, Benjamin Tissoires wrote: > Previously, HID-BPF was relying on a bpf tracing program to be notified > when a program was released from userspace. This is error prone, as > LLVM sometimes inline the function and sometimes not. > > So instead of messing up with the bpf prog ref count, we can use the > bpf_link concept which actually matches exactly what we want: > - a bpf_link represents the fact that a given program is attached to a > given HID device > - as long as the bpf_link has fd opened (either by the userspace program > still being around or by pinning the bpf object in the bpffs), the > program stays attached to the HID device > - once every user has closed the fd, we get called by > hid_bpf_link_release() that we no longer have any users, and we can > disconnect the program to the device in 2 passes: first atomically clear > the bit saying that the link is active, and then calling release_work in > a scheduled work item. > > This solves entirely the problems of BPF tracing not showing up and is > definitely cleaner. > > Signed-off-by: Benjamin Tissoires <benjamin.tissoires@xxxxxxxxxx> Acked-by: Alexei Starovoitov <ast@xxxxxxxxxx>
