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

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Date:	Mon, 18 May 2015 11:48:57 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Wang Nan <wangnan0@...wei.com>, paulus@...ba.org,
	a.p.zijlstra@...llo.nl, mingo@...hat.com, acme@...nel.org,
	namhyung@...nel.org, jolsa@...nel.org, dsahern@...il.com,
	daniel@...earbox.net, brendan.d.gregg@...il.com,
	masami.hiramatsu.pt@...achi.com
CC:	lizefan@...wei.com, linux-kernel@...r.kernel.org, pi3orama@....com
Subject: Re: [RFC PATCH v3 21/37] bpf tools: Create eBPF maps defined in an
 object file

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@...wei.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:

> +			}
> +			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.

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