On Thu, Jun 27, 2024 at 11:28 PM Masami Hiramatsu wrote:
>
> On Thu, 27 Jun 2024 09:47:10 -0700
> Andrii Nakryiko wrote:
>
> > On Thu, Jun 27, 2024 at 6:04 AM Masami Hiramatsu
> > wrote:
> > >
> > > On Mon, 24 Jun 2024 17:21:38 -0700
> > > Andrii Nakryiko wrote:
> > >
> > > > -static int __uprobe_register(struct inode *inode, loff_t offset,
> > > > - loff_t ref_ctr_offset, struct
> > > > uprobe_consumer *uc)
> > > > +int uprobe_register_batch(struct inode *inode, int cnt,
> > > > + uprobe_consumer_fn get_uprobe_consumer, void
> > > > *ctx)
> > >
> > > Is this interface just for avoiding memory allocation? Can't we just
> > > allocate a temporary array of *uprobe_consumer instead?
> >
> > Yes, exactly, to avoid the need for allocating another array that
> > would just contain pointers to uprobe_consumer. Consumers would never
> > just have an array of `struct uprobe_consumer *`, because
> > uprobe_consumer struct is embedded in some other struct, so the array
> > interface isn't the most convenient.
>
> OK, I understand it.
>
> >
> > If you feel strongly, I can do an array, but this necessitates
> > allocating an extra array *and keeping it* for the entire duration of
> > BPF multi-uprobe link (attachment) existence, so it feels like a
> > waste. This is because we don't want to do anything that can fail in
> > the detachment logic (so no temporary array allocation there).
>
> No need to change it, that sounds reasonable.
>
Great, thanks.
> >
> > Anyways, let me know how you feel about keeping this callback.
>
> IMHO, maybe the interface function is better to change to
> `uprobe_consumer *next_uprobe_consumer(void **data)`. If caller
> side uses a linked list of structure, index access will need to
> follow the list every time.
This would be problematic. Note how we call get_uprobe_consumer(i,
ctx) with i going from 0 to N in multiple independent loops. So if we
are only allowed to ask for the next consumer, then
uprobe_register_batch and uprobe_unregister_batch would need to build
its own internal index and remember ith instance. Which again means
more allocations and possibly failing uprobe_unregister_batch(), which
isn't great.
For now this API works well, I propose to keep it as is. For linked
list case consumers would need to allocate one extra array or pay the
price of O(N) search (which might be ok, depending on how many uprobes
are being attached). But we don't have such consumers right now,
thankfully.
>
> Thank you,
>
>
> >
> > >
> > > Thank you,
> > >
> > > --
> > > Masami Hiramatsu (Google)
>
>
> --
> Masami Hiramatsu (Google)
