Re: [PATCH 06/12] uprobes: add batch uprobe register/unregister APIs

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Thu, 27 Jun 2024 09:47:10 -0700
Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:

> On Thu, Jun 27, 2024 at 6:04 AM Masami Hiramatsu <mhiramat@kernel.org> wrote:
> >
> > On Mon, 24 Jun 2024 17:21:38 -0700
> > Andrii Nakryiko <andrii@kernel.org> 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.

> 
> 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.

Thank you,


> 
> >
> > Thank you,
> >
> > --
> > Masami Hiramatsu (Google) <mhiramat@kernel.org>


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>