On Thu, 28 Jul 2022 at 07:25, Kui-Feng Lee <kuifeng@xxxxxx> wrote:
>
> On Wed, 2022-07-27 at 10:19 +0200, Kumar Kartikeya Dwivedi wrote:
> > On Wed, 27 Jul 2022 at 09:01, Kui-Feng Lee <kuifeng@xxxxxx> wrote:
> > >
> > > On Tue, 2022-07-26 at 14:13 +0200, Jiri Olsa wrote:
> > > > On Mon, Jul 25, 2022 at 10:17:11PM -0700, Kui-Feng Lee wrote:
> > > > > Allow creating an iterator that loops through resources of one
> > > > > task/thread.
> > > > >
> > > > > People could only create iterators to loop through all
> > > > > resources of
> > > > > files, vma, and tasks in the system, even though they were
> > > > > interested
> > > > > in only the resources of a specific task or process. Passing
> > > > > the
> > > > > additional parameters, people can now create an iterator to go
> > > > > through all resources or only the resources of a task.
> > > > >
> > > > > Signed-off-by: Kui-Feng Lee <kuifeng@xxxxxx>
> > > > > ---
> > > > > include/linux/bpf.h | 4 ++
> > > > > include/uapi/linux/bpf.h | 23 ++++++++++
> > > > > kernel/bpf/task_iter.c | 81 +++++++++++++++++++++++++-
> > > > > ----
> > > > > ----
> > > > > tools/include/uapi/linux/bpf.h | 23 ++++++++++
> > > > > 4 files changed, 109 insertions(+), 22 deletions(-)
> > > > >
> > > > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > > > > index 11950029284f..c8d164404e20 100644
> > > > > --- a/include/linux/bpf.h
> > > > > +++ b/include/linux/bpf.h
> > > > > @@ -1718,6 +1718,10 @@ int bpf_obj_get_user(const char __user
> > > > > *pathname, int flags);
> > > > >
> > > > > struct bpf_iter_aux_info {
> > > > > struct bpf_map *map;
> > > > > + struct {
> > > > > + __u32 tid;
> > > >
> > > > should be just u32 ?
> > >
> > > Or, should change the following 'type' to __u8?
> >
> > Would it be better to use a pidfd instead of a tid here? Unset pidfd
> > would mean going over all tasks, and any fd > 0 implies attaching to
> > a
> > specific task (as is the convention in BPF land). Most of the new
> > UAPIs working on processes are using pidfds (to work with a stable
> > handle instead of a reusable ID).
> > The iterator taking an fd also gives an opportunity to BPF LSMs to
> > attach permissions/policies to it (once we have a file local storage
> > map) e.g. whether creating a task iterator for that specific pidfd
> > instance (backed by the struct file) would be allowed or not.
> > You are using getpid in the selftest and keeping track of last_tgid
> > in
> > the iterator, so I guess you don't even need to extend pidfd_open to
> > work on thread IDs right now for your use case (and fdtable and mm
> > are
> > shared for POSIX threads anyway, so for those two it won't make a
> > difference).
> >
> > What is your opinion?
>
> Do you mean removed both tid and type, and replace them with a pidfd?
> We can do that in uapi, struct bpf_link_info. But, the interal types,
> ex. bpf_iter_aux_info, still need to use tid or struct file to avoid
> getting file from the per-process fdtable. Is that what you mean?
>
Yes, just for the UAPI, it is similar to taking map_fd for map iter.
In bpf_link_info we should report just the tid, just like map iter
reports map_id.
