On Tue, Jan 14, 2020 at 10:04 PM Martin Lau <kafai@xxxxxx> wrote:
>
> On Tue, Jan 14, 2020 at 05:49:00PM -0800, Andrii Nakryiko wrote:
> > On Tue, Jan 14, 2020 at 2:46 PM Martin KaFai Lau <kafai@xxxxxx> wrote:
> > >
> > > This patch makes bpftool support dumping a map's value properly
> > > when the map's value type is a type of the running kernel's btf.
> > > (i.e. map_info.btf_vmlinux_value_type_id is set instead of
> > > map_info.btf_value_type_id). The first usecase is for the
> > > BPF_MAP_TYPE_STRUCT_OPS.
> > >
> > > Signed-off-by: Martin KaFai Lau <kafai@xxxxxx>
> > > ---
> > > tools/bpf/bpftool/map.c | 43 +++++++++++++++++++++++++++++++----------
> > > 1 file changed, 33 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
> > > index 4c5b15d736b6..d25f3b2355ad 100644
> > > --- a/tools/bpf/bpftool/map.c
> > > +++ b/tools/bpf/bpftool/map.c
> > > @@ -20,6 +20,7 @@
> > > #include "btf.h"
> > > #include "json_writer.h"
> > > #include "main.h"
> > > +#include "libbpf_internal.h"
> > >
> > > const char * const map_type_name[] = {
> > > [BPF_MAP_TYPE_UNSPEC] = "unspec",
> > > @@ -252,6 +253,7 @@ static int do_dump_btf(const struct btf_dumper *d,
> > > struct bpf_map_info *map_info, void *key,
> > > void *value)
> > > {
> > > + __u32 value_id;
> > > int ret;
> > >
> > > /* start of key-value pair */
> > > @@ -265,9 +267,12 @@ static int do_dump_btf(const struct btf_dumper *d,
> > > goto err_end_obj;
> > > }
> > >
> > > + value_id = map_info->btf_vmlinux_value_type_id ?
> > > + : map_info->btf_value_type_id;
> > > +
> > > if (!map_is_per_cpu(map_info->type)) {
> > > jsonw_name(d->jw, "value");
> > > - ret = btf_dumper_type(d, map_info->btf_value_type_id, value);
> > > + ret = btf_dumper_type(d, value_id, value);
> > > } else {
> > > unsigned int i, n, step;
> > >
> > > @@ -279,8 +284,7 @@ static int do_dump_btf(const struct btf_dumper *d,
> > > jsonw_start_object(d->jw);
> > > jsonw_int_field(d->jw, "cpu", i);
> > > jsonw_name(d->jw, "value");
> > > - ret = btf_dumper_type(d, map_info->btf_value_type_id,
> > > - value + i * step);
> > > + ret = btf_dumper_type(d, value_id, value + i * step);
> > > jsonw_end_object(d->jw);
> > > if (ret)
> > > break;
> > > @@ -932,6 +936,27 @@ static int maps_have_btf(int *fds, int nb_fds)
> > > return 1;
> > > }
> > >
> > > +static struct btf *get_map_kv_btf(const struct bpf_map_info *info)
> > > +{
> > > + struct btf *btf = NULL;
> > > +
> > > + if (info->btf_vmlinux_value_type_id) {
> > > + btf = bpf_find_kernel_btf();
> >
> > If there are multiple maps we are dumping, it might become quite
> > costly to re-read and re-parse kernel BTF all the time. Can we lazily
> > load it, when required,
> It is loaded lazily.
>
yeah, it was meant as "lazy load and cache" vs "pre-load always"
(which makes caching simpler).
> > and cache instead?
> Cache it in bpftool/map.c? Sure.
yeah, for the duration of dumping
>
> >
> > > + if (IS_ERR(btf))
> > > + p_err("failed to get kernel btf");
> > > + } else if (info->btf_value_type_id) {
> > > + int err;
> > > +
> > > + err = btf__get_from_id(info->btf_id, &btf);
> > > + if (err || !btf) {
> > > + p_err("failed to get btf");
> > > + btf = err ? ERR_PTR(err) : ERR_PTR(-ESRCH);
> > > + }
> > > + }
> > > +
> > > + return btf;
> > > +}
> > > +
> > > static int
> > > map_dump(int fd, struct bpf_map_info *info, json_writer_t *wtr,
> > > bool show_header)
> > > @@ -952,13 +977,11 @@ map_dump(int fd, struct bpf_map_info *info, json_writer_t *wtr,
> > > prev_key = NULL;
> > >
> > > if (wtr) {
> > > - if (info->btf_id) {
> > > - err = btf__get_from_id(info->btf_id, &btf);
> > > - if (err || !btf) {
> > > - err = err ? : -ESRCH;
> > > - p_err("failed to get btf");
> > > - goto exit_free;
> > > - }
> > > + btf = get_map_kv_btf(info);
> > > + if (IS_ERR(btf)) {
> > > + err = PTR_ERR(btf);
> > > + btf = NULL;
> > > + goto exit_free;
> > > }
> > >
> > > if (show_header) {
> > > --
> > > 2.17.1
> > >
