Re: [PATCH bpf-next v5 4/5] bpf: Make fs kfuncs available for SYSCALL and TRACING program types

[Juntong Deng]

On 2024/12/10 18:58, Alexei Starovoitov wrote:
> On Tue, Dec 10, 2024 at 6:43 AM Christian Brauner <brauner@xxxxxxxxxx> wrote:
> > On Tue, Dec 10, 2024 at 02:03:53PM +0000, Juntong Deng wrote:
> > > Currently fs kfuncs are only available for LSM program type, but fs
> > > kfuncs are generic and useful for scenarios other than LSM.
> > >
> > > This patch makes fs kfuncs available for SYSCALL and TRACING
> > > program types.
> >
> > I would like a detailed explanation from the maintainers what it means
> > to make this available to SYSCALL program types, please.
>
> Sigh.
> This is obviously not safe from tracing progs.
>
>  From BPF_PROG_TYPE_SYSCALL these kfuncs should be safe to use,
> since those progs are not attached to anything.
> Such progs can only be executed via sys_bpf syscall prog_run command.
> They're sleepable, preemptable, faultable, in task ctx.
>
> But I'm not sure what's the value of enabling these kfuncs for
> BPF_PROG_TYPE_SYSCALL.

Thanks for your reply.

Song said here that we need some of these kfuncs to be available for
tracing functions [0].

If Song saw this email, could you please join the discussion?

[0]: 
https://lore.kernel.org/bpf/CAPhsuW6ud21v2xz8iSXf=CiDL+R_zpQ+p8isSTMTw=EiJQtRSw@xxxxxxxxxxxxxx/

For BPF_PROG_TYPE_SYSCALL, I think BPF_PROG_TYPE_SYSCALL has now
exceeded its original designed purpose and has become a more general
program type.

Currently BPF_PROG_TYPE_SYSCALL is widely used in HID drivers, and there
are some use cases in sched-ext (CRIB is also a use case, although still
in infancy).

As BPF_PROG_TYPE_SYSCALL becomes more general, it would be valuable to
make more kfuncs available for BPF_PROG_TYPE_SYSCALL.