On Thu, Apr 18, 2024 at 9:35 AM Kui-Feng Lee <thinker.li@xxxxxxxxx> wrote: > > Add the "open" operator for the inodes of BPF links to allow applications > to obtain a file descriptor of a struct_ops link from a pinned path. > > Applications have the ability to update a struct_ops link with another > struct_ops map. However, they were unable to open pinned paths of the links > with this patch. This implies that updating a link through its pinned paths > was not feasible. > > This patch adds the "open" operator to bpf_link_ops and uses bpf_link_ops > as the i_fop for inodes of struct_ops links. "open" will be called to open > the pinned path represented by an inode. Additionally, bpf_link_ops will be > used as the f->f_ops of the opened "file" to provide operators for the > "file". > > Signed-off-by: Kui-Feng Lee <thinker.li@xxxxxxxxx> > --- > include/linux/bpf.h | 6 ++++++ > kernel/bpf/bpf_struct_ops.c | 10 ++++++++++ > kernel/bpf/inode.c | 11 ++++++++--- > kernel/bpf/syscall.c | 16 +++++++++++++++- > 4 files changed, 39 insertions(+), 4 deletions(-) > This is already supported, but you don't do it with open() syscall. bpf() syscall provides BPF_OBJ_GET as a counterpart to BPF_OBJ_PIN. So what you/your users want to do should be already supported through libbpf's bpf_obj_get()/bpf_obj_get_ops() APIs. Have you tried that? > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > index 5034c1b4ded7..a0c0234d754b 100644 > --- a/include/linux/bpf.h > +++ b/include/linux/bpf.h > @@ -2160,6 +2160,12 @@ extern const struct super_operations bpf_super_ops; > extern const struct file_operations bpf_map_fops; > extern const struct file_operations bpf_prog_fops; > extern const struct file_operations bpf_iter_fops; > +extern const struct file_operations bpf_link_fops; > + [...]
