Re: [RFC PATCH v3 21/37] bpf tools: Create eBPF maps defined in an object file

Arnaldo Carvalho de Melo
2015-05-18T20:37:07Z

Em Mon, May 18, 2015 at 11:48:57AM -0700, Alexei Starovoitov escreveu:
> On 5/17/15 3:56 AM, Wang Nan wrote:
> >This patch creates maps based on 'map' section in object file using
> >bpf_create_map(), and store the fds into an array in
> >'struct bpf_object'. Since the byte order of the object may differ
> >from the host, swap map definition before processing.
> >
> >This is the first patch in 'loading' phase. Previous patches parse ELF
> >object file and create needed data structure, but doesnnt play with
> >kernel. They belong to 'opening' phase.
> >
> >Signed-off-by: Wang Nan <wangnan0@huawei.com>
> ...
> >+ for (j = 0; j < i; j++) {
> >+ close(obj->maps_fds[j]);
> >+ obj->maps_fds[j] = -1;
>
> this line is unnecessary, since you're freeing the whole array
> at the line below:

I guess this is kinda of a zfree() that he wants to achieve, i.e. if a
bug creeps in that makes some code use the deleted maps_fds, he rather
wants it to access a -1 fd than an some reused fd, no?

> >+ }
> >+ free(obj->maps_fds);

> >+ obj->maps_fds = NULL;
>
> ...
>
> > void bpf_close_object(struct bpf_object *obj)
> > {
> > if (!obj)
> > return;
> >
> > bpf_obj_clear_elf(obj);
> >+ bpf_unload_object(obj);
>
> just realized that this API keeps elf file open for the whole
> life time. I think that should be split up.
> bpf_open_object() can do elf parsing, creation of maps and
> bpf loading.
> bpf_close_object() can unload programs, maps. That's fine,
> but closing of elf file and freeing memory associated
> with parsing sections should be a separate call.