On Mon, 31 Jul 2023 14:59:47 -0700
Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote:
> On Mon, Jul 31, 2023 at 12:30 AM Masami Hiramatsu (Google)
> <mhiramat@xxxxxxxxxx> wrote:
> >
> > From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> >
> > Add btf_find_struct_member() API to search a member of a given data structure
> > or union from the member's name.
> >
> > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> > Reviewed-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> > ---
> > Changes in v3:
> > - Remove simple input check.
> > - Fix unneeded IS_ERR_OR_NULL() check for btf_type_by_id().
> > - Move the code next to btf_get_func_param().
> > - Use for_each_member() macro instead of for-loop.
> > - Use btf_type_skip_modifiers() instead of btf_type_by_id().
> > Changes in v4:
> > - Use a stack for searching in anonymous members instead of nested call.
> > ---
> > include/linux/btf.h | 3 +++
> > kernel/bpf/btf.c | 40 ++++++++++++++++++++++++++++++++++++++++
> > 2 files changed, 43 insertions(+)
> >
> > diff --git a/include/linux/btf.h b/include/linux/btf.h
> > index 20e3a07eef8f..4b10d57ceee0 100644
> > --- a/include/linux/btf.h
> > +++ b/include/linux/btf.h
> > @@ -226,6 +226,9 @@ const struct btf_type *btf_find_func_proto(const char *func_name,
> > struct btf **btf_p);
> > const struct btf_param *btf_get_func_param(const struct btf_type *func_proto,
> > s32 *nr);
> > +const struct btf_member *btf_find_struct_member(struct btf *btf,
> > + const struct btf_type *type,
> > + const char *member_name);
> >
> > #define for_each_member(i, struct_type, member) \
> > for (i = 0, member = btf_type_member(struct_type); \
> > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > index f7b25c615269..8d81a4ffa67b 100644
> > --- a/kernel/bpf/btf.c
> > +++ b/kernel/bpf/btf.c
> > @@ -958,6 +958,46 @@ const struct btf_param *btf_get_func_param(const struct btf_type *func_proto, s3
> > return NULL;
> > }
> >
> > +#define BTF_ANON_STACK_MAX 16
> > +
> > +/*
> > + * Find a member of data structure/union by name and return it.
> > + * Return NULL if not found, or -EINVAL if parameter is invalid.
> > + */
> > +const struct btf_member *btf_find_struct_member(struct btf *btf,
> > + const struct btf_type *type,
> > + const char *member_name)
> > +{
> > + const struct btf_type *anon_stack[BTF_ANON_STACK_MAX];
> > + const struct btf_member *member;
> > + const char *name;
> > + int i, top = 0;
> > +
> > +retry:
> > + if (!btf_type_is_struct(type))
> > + return ERR_PTR(-EINVAL);
> > +
> > + for_each_member(i, type, member) {
> > + if (!member->name_off) {
> > + /* Anonymous union/struct: push it for later use */
> > + type = btf_type_skip_modifiers(btf, member->type, NULL);
> > + if (type && top < BTF_ANON_STACK_MAX)
> > + anon_stack[top++] = type;
> > + } else {
> > + name = btf_name_by_offset(btf, member->name_off);
> > + if (name && !strcmp(member_name, name))
> > + return member;
> > + }
> > + }
> > + if (top > 0) {
> > + /* Pop from the anonymous stack and retry */
> > + type = anon_stack[--top];
> > + goto retry;
> > + }
>
> Looks good, but I don't see a test case for this.
> The logic is a bit tricky. I'd like to have a selftest that covers it.
Thanks, and I agree about selftest.
>
> You probably need to drop Alan's reviewed-by, since the patch is quite
> different from the time he reviewed it.
OK. BTW, I found a problem on this function. I guess the member->offset will
be the offset from the intermediate anonymous union, it is usually 0, but
I need the offset from the given structure. Thus the interface design must
be changed. Passing a 'u32 *offset' and set the correct offset in it. If
it has nested intermediate anonymous unions, that offset must also be pushed.
>
> Assuming that is addressed. How do we merge the series?
> The first 3 patches have serious conflicts with bpf trees.
>
> Maybe send the first 3 with extra selftest for above recursion
> targeting bpf-next then we can have a merge commit that Steven can pull
> into tracing?
>
> Or if we can have acks for patches 4-9 we can pull the whole set into bpf-next.
That's a good question. I don't like splitting the whole series in 2 -next
branches. So I can send this to the bpf-next.
I need to work on another series(*) on fprobes which will not have conflicts with
this series. (*Replacing pt_regs with ftrace_regs on fprobe, which will take longer
time, and need to adjust with eBPF).
Thank you,
--
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
