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Date: Thu, 21 Jun 2018 11:05:21 +0100
From: Okash Khawaja <osk@...com>
To: Song Liu <songliubraving@...com>
CC: Daniel Borkmann <daniel@...earbox.net>, Martin Lau <kafai@...com>,
Alexei Starovoitov <ast@...nel.org>,
Yonghong Song <yhs@...com>,
Quentin Monnet <quentin.monnet@...ronome.com>,
Jakub Kicinski <jakub.kicinski@...ronome.com>,
"David S. Miller" <davem@...emloft.net>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
Kernel Team <Kernel-team@...com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next 3/3] bpf: btf: json print map dump with btf info
On Thu, Jun 21, 2018 at 12:22:52AM +0100, Song Liu wrote:
>
>
> > On Jun 20, 2018, at 1:30 PM, Okash Khawaja <osk@...com> wrote:
> >
> > This patch modifies `bpftool map dump [-j|-p] id <map-id>` to json-
> > print and pretty-json-print map dump. It calls btf_dumper introduced in
> > previous patch to accomplish this.
> >
> > The patch only prints debug info when -j or -p flags are supplied. Then
> > too, if the map has associated btf data loaded. Otherwise the usual
> > debug-less output is printed.
> >
> > Signed-off-by: Okash Khawaja <osk@...com>
> > Acked-by: Martin KaFai Lau <kafai@...com>
> >
> > ---
> > tools/bpf/bpftool/map.c | 94 ++++++++++++++++++++++++++++++++++++++++++++++--
> > 1 file changed, 91 insertions(+), 3 deletions(-)
> >
> > --- a/tools/bpf/bpftool/map.c
> > +++ b/tools/bpf/bpftool/map.c
> > @@ -43,9 +43,13 @@
> > #include <unistd.h>
> > #include <sys/types.h>
> > #include <sys/stat.h>
> > +#include <linux/err.h>
> >
> > #include <bpf.h>
> >
> > +#include "json_writer.h"
> > +#include "btf.h"
> > +#include "btf_dumper.h"
> > #include "main.h"
> >
> > static const char * const map_type_name[] = {
> > @@ -508,6 +512,83 @@ static int do_show(int argc, char **argv
> > return errno == ENOENT ? 0 : -1;
> > }
> >
> > +
> > +static int do_dump_btf(struct btf *btf, struct bpf_map_info *map_info,
> > + void *key, void *value)
> > +{
> > + int ret;
> > +
> > + jsonw_start_object(json_wtr);
> > + jsonw_name(json_wtr, "key");
> > +
> > + ret = btf_dumper_type(btf, json_wtr, map_info->btf_key_type_id, key);
> > + if (ret)
> > + goto out;
> > +
> > + jsonw_end_object(json_wtr);
> > +
> > + jsonw_start_object(json_wtr);
> > + jsonw_name(json_wtr, "value");
> > +
> > + ret = btf_dumper_type(btf, json_wtr, map_info->btf_value_type_id,
> > + value);
> > +
> > +out:
> > + /* end of root object */
> > + jsonw_end_object(json_wtr);
> > +
> > + return ret;
> > +}
>
> Please add some tests for do_dump_btf(), including some invalid data type/kind.
Sure. I was wondering if we can follow this up with tests afterwards.
However if they are essential now, I can add them.
>
> > +
> > +static struct btf *get_btf(struct bpf_map_info *map_info)
> > +{
> > + int btf_fd = bpf_btf_get_fd_by_id(map_info->btf_id);
> > + struct bpf_btf_info btf_info = { 0 };
> > + __u32 len = sizeof(btf_info);
> > + uint32_t last_size;
> > + int err;
> > + struct btf *btf = NULL;
> > + void *ptr = NULL, *temp_ptr;
> > +
> > + if (btf_fd < 0)
> > + return NULL;
> > +
> > + btf_info.btf_size = 4096;
>
> Is btf_size always a constant of 4096?
We start out with 4096 and in the loop below we increase the size if
needed. It seems like a sane valeu to start with. However if there are
better ideas for start value, we can discuss them.
>
> > + do {
> > + last_size = btf_info.btf_size;
> > + temp_ptr = realloc(ptr, last_size);
> > + if (!temp_ptr) {
> > + p_err("unable allocate memory for debug info.");
> > + goto exit_free;
> > + }
> > +
> > + ptr = temp_ptr;
> > + bzero(ptr, last_size);
> > + btf_info.btf = ptr_to_u64(ptr);
> > + err = bpf_obj_get_info_by_fd(btf_fd, &btf_info, &len);
> > + } while (!err && btf_info.btf_size > last_size && last_size == 4096);
> > +
> > + if (err || btf_info.btf_size > last_size) {
> > + p_info("can't get btf info. debug info won't be displayed. error: %s",
> > + err ? strerror(errno) : "exceeds size retry");
> > + goto exit_free;
> > + }
> > +
> > + btf = btf__new((uint8_t *) btf_info.btf,
> > + btf_info.btf_size, NULL);
> > + if (IS_ERR(btf)) {
> > + printf("error when initialising btf: %s\n",
> > + strerror(PTR_ERR(btf)));
> > + btf = NULL;
> > + }
> > +
> > +exit_free:
> > + close(btf_fd);
> > + free(ptr);
> > +
> > + return btf;
> > +}
> > +
> > static int do_dump(int argc, char **argv)
> > {
> > void *key, *value, *prev_key;
> > @@ -516,6 +597,7 @@ static int do_dump(int argc, char **argv
> > __u32 len = sizeof(info);
> > int err;
> > int fd;
> > + struct btf *btf = NULL;
> >
> > if (argc != 2)
> > usage();
> > @@ -538,6 +620,8 @@ static int do_dump(int argc, char **argv
> > goto exit_free;
> > }
> >
> > + btf = get_btf(&info);
> > +
> > prev_key = NULL;
> > if (json_output)
> > jsonw_start_array(json_wtr);
> > @@ -550,9 +634,12 @@ static int do_dump(int argc, char **argv
> > }
> >
> > if (!bpf_map_lookup_elem(fd, key, value)) {
> > - if (json_output)
> > - print_entry_json(&info, key, value);
> > - else
> > + if (json_output) {
> > + if (btf)
> > + do_dump_btf(btf, &info, key, value);
> > + else
> > + print_entry_json(&info, key, value);
> > + } else
> > print_entry_plain(&info, key, value);
> > } else {
> > if (json_output) {
> > @@ -584,6 +671,7 @@ exit_free:
> > free(key);
> > free(value);
> > close(fd);
> > + btf__free(btf);
> >
> > return err;
> > }
> >
>
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