Re: [PATCH bpf-next v3 18/21] tools/bpftool: add bpf_iter support for bptool

Yonghong Song
2020-05-09T05:27:13Z

On 5/8/20 12:51 PM, Andrii Nakryiko wrote:
> On Wed, May 6, 2020 at 10:40 PM Yonghong Song <yhs@fb.com> wrote:
>>
>> Currently, only one command is supported
>> bpftool iter pin <bpf_prog.o> <path>
>>
>> It will pin the trace/iter bpf program in
>> the object file <bpf_prog.o> to the <path>
>> where <path> should be on a bpffs mount.
>>
>> For example,
>> $ bpftool iter pin ./bpf_iter_ipv6_route.o \
>> /sys/fs/bpf/my_route
>> User can then do a `cat` to print out the results:
>> $ cat /sys/fs/bpf/my_route
>> fe800000000000000000000000000000 40 00000000000000000000000000000000 ...
>> 00000000000000000000000000000000 00 00000000000000000000000000000000 ...
>> 00000000000000000000000000000001 80 00000000000000000000000000000000 ...
>> fe800000000000008c0162fffebdfd57 80 00000000000000000000000000000000 ...
>> ff000000000000000000000000000000 08 00000000000000000000000000000000 ...
>> 00000000000000000000000000000000 00 00000000000000000000000000000000 ...
>>
>> The implementation for ipv6_route iterator is in one of subsequent
>> patches.
>>
>> This patch also added BPF_LINK_TYPE_ITER to link query.
>>
>> In the future, we may add additional parameters to pin command
>> by parameterizing the bpf iterator. For example, a map_id or pid
>> may be added to let bpf program only traverses a single map or task,
>> similar to kernel seq_file single_open().
>>
>> We may also add introspection command for targets/iterators by
>> leveraging the bpf_iter itself.
>>
>> Signed-off-by: Yonghong Song <yhs@fb.com>
>> ---
>> .../bpftool/Documentation/bpftool-iter.rst | 83 ++++++++++++++++++
>> tools/bpf/bpftool/bash-completion/bpftool | 13 +++
>> tools/bpf/bpftool/iter.c | 84 +++++++++++++++++++
>> tools/bpf/bpftool/link.c | 1 +
>> tools/bpf/bpftool/main.c | 3 +-
>> tools/bpf/bpftool/main.h | 1 +
>> 6 files changed, 184 insertions(+), 1 deletion(-)
>> create mode 100644 tools/bpf/bpftool/Documentation/bpftool-iter.rst
>> create mode 100644 tools/bpf/bpftool/iter.c
>>
>
> [...]
>
>> diff --git a/tools/bpf/bpftool/iter.c b/tools/bpf/bpftool/iter.c
>> new file mode 100644
>> index 000000000000..a8fb1349c103
>> --- /dev/null
>> +++ b/tools/bpf/bpftool/iter.c
>> @@ -0,0 +1,84 @@
>> +// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>> +// Copyright (C) 2020 Facebook
>> +
>> +#define _GNU_SOURCE
>> +#include <linux/err.h>
>> +#include <bpf/libbpf.h>
>> +
>> +#include "main.h"
>> +
>> +static int do_pin(int argc, char **argv)
>> +{
>> + const char *objfile, *path;
>> + struct bpf_program *prog;
>> + struct bpf_object *obj;
>> + struct bpf_link *link;
>> + int err;
>> +
>> + if (!REQ_ARGS(2))
>> + usage();
>> +
>> + objfile = GET_ARG();
>> + path = GET_ARG();
>> +
>> + obj = bpf_object__open(objfile);
>> + if (IS_ERR_OR_NULL(obj)) {
>
> nit: can't be NULL

Ack. Will change.

>
>> + p_err("can't open objfile %s", objfile);
>> + return -1;
>> + }
>> +
>> + err = bpf_object__load(obj);
>> + if (err) {
>> + p_err("can't load objfile %s", objfile);
>> + goto close_obj;
>> + }
>> +
>> + prog = bpf_program__next(NULL, obj);
>
> check for null and printf error? Crashing is not good.

Make sense. Will change.

>
>> + link = bpf_program__attach_iter(prog, NULL);
>> + if (IS_ERR(link)) {
>> + err = PTR_ERR(link);
>> + p_err("attach_iter failed for program %s",
>> + bpf_program__name(prog));
>> + goto close_obj;
>> + }
>> +
>> + err = mount_bpffs_for_pin(path);
>> + if (err)
>> + goto close_link;
>> +
>> + err = bpf_link__pin(link, path);
>> + if (err) {
>> + p_err("pin_iter failed for program %s to path %s",
>> + bpf_program__name(prog), path);
>> + goto close_link;
>> + }
>> +
>> +close_link:
>> + bpf_link__disconnect(link);
>
> this is wrong, just destroy()

Will change.

>
>> + bpf_link__destroy(link);
>> +close_obj:
>> + bpf_object__close(obj);
>> + return err;
>> +}
>> +
>
> [...]
>