Re: [PATCH 1/2] perf util: move bperf definitions to a libperf header

[Jiri Olsa <jolsa@redhat.com>]

On Fri, Apr 02, 2021 at 05:29:37PM -0700, Song Liu wrote:
> By following the same protocol, other tools can share hardware PMCs with
> perf. Move perf_event_attr_map_entry and BPERF_DEFAULT_ATTR_MAP_PATH to
> bperf.h for other tools to use.

hi,
so is this necessary for some other tool now?

> 
> Also add bperf_attr_map_compatible() to check whether existing attr_map
> is compatible with current perf binary.

please separate this change

> 
> Signed-off-by: Song Liu <song@kernel.org>
> ---
>  tools/lib/perf/include/perf/bperf.h | 29 +++++++++++++++++++
>  tools/perf/util/bpf_counter.c       | 44 ++++++++++++++---------------
>  2 files changed, 50 insertions(+), 23 deletions(-)
>  create mode 100644 tools/lib/perf/include/perf/bperf.h
> 
> diff --git a/tools/lib/perf/include/perf/bperf.h b/tools/lib/perf/include/perf/bperf.h
> new file mode 100644
> index 0000000000000..02b2fd5e50c75
> --- /dev/null
> +++ b/tools/lib/perf/include/perf/bperf.h

I wonder we want to call it bpf_perf.h to be more generic?
or best just bpf.h ... but that might give us some conflict
headache in future ;-)

> @@ -0,0 +1,29 @@
> +/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
> +#ifndef __LIBPERF_BPERF_H
> +#define __LIBPERF_BPERF_H
> +
> +/*
> + * bperf uses a hashmap, the attr_map, to track all the leader programs.
> + * The hashmap is pinned in bpffs. flock() on this file is used to ensure
> + * no concurrent access to the attr_map.  The key of attr_map is struct
> + * perf_event_attr, and the value is struct perf_event_attr_map_entry.
> + *
> + * struct perf_event_attr_map_entry contains two __u32 IDs, bpf_link of the
> + * leader prog, and the diff_map. Each perf-stat session holds a reference
> + * to the bpf_link to make sure the leader prog is attached to sched_switch
> + * tracepoint.
> + *
> + * Since the hashmap only contains IDs of the bpf_link and diff_map, it
> + * does not hold any references to the leader program. Once all perf-stat
> + * sessions of these events exit, the leader prog, its maps, and the
> + * perf_events will be freed.
> + */
> +struct perf_event_attr_map_entry {
> +	__u32 link_id;
> +	__u32 diff_map_id;
> +};

this header file should be self contained,
so you need __u32 definitions


> +
> +/* pin the map at sysfs__mountpoint()/BPERF_DEFAULT_ATTR_MAP_PATH */
> +#define BPERF_DEFAULT_ATTR_MAP_PATH "fs/bpf/perf_attr_map"

if we are going to expose this, I think we should expose just
"perf_attr_map" ... without the 'fs/bpf' part, because that
could be mounted anywhere

thanks,
jirka

> +
> +#endif /* __LIBPERF_BPERF_H */
> diff --git a/tools/perf/util/bpf_counter.c b/tools/perf/util/bpf_counter.c
> index 81d1df3c4ec0e..df70c8dcf7850 100644
> --- a/tools/perf/util/bpf_counter.c
> +++ b/tools/perf/util/bpf_counter.c
> @@ -14,6 +14,7 @@
>  #include <bpf/btf.h>
>  #include <bpf/libbpf.h>
>  #include <api/fs/fs.h>
> +#include <perf/bperf.h>
>  
>  #include "bpf_counter.h"
>  #include "counts.h"
> @@ -29,28 +30,6 @@
>  #include "bpf_skel/bperf_leader.skel.h"
>  #include "bpf_skel/bperf_follower.skel.h"
>  
> -/*
> - * bperf uses a hashmap, the attr_map, to track all the leader programs.
> - * The hashmap is pinned in bpffs. flock() on this file is used to ensure
> - * no concurrent access to the attr_map.  The key of attr_map is struct
> - * perf_event_attr, and the value is struct perf_event_attr_map_entry.
> - *
> - * struct perf_event_attr_map_entry contains two __u32 IDs, bpf_link of the
> - * leader prog, and the diff_map. Each perf-stat session holds a reference
> - * to the bpf_link to make sure the leader prog is attached to sched_switch
> - * tracepoint.
> - *
> - * Since the hashmap only contains IDs of the bpf_link and diff_map, it
> - * does not hold any references to the leader program. Once all perf-stat
> - * sessions of these events exit, the leader prog, its maps, and the
> - * perf_events will be freed.
> - */
> -struct perf_event_attr_map_entry {
> -	__u32 link_id;
> -	__u32 diff_map_id;
> -};
> -
> -#define DEFAULT_ATTR_MAP_PATH "fs/bpf/perf_attr_map"
>  #define ATTR_MAP_SIZE 16
>  
>  static inline void *u64_to_ptr(__u64 ptr)
> @@ -333,6 +312,20 @@ static __u32 bpf_map_get_id(int fd)
>  	return map_info.id;
>  }
>  
> +static bool bperf_attr_map_compatible(int attr_map_fd)
> +{
> +	struct bpf_map_info map_info = {0};
> +	__u32 map_info_len = sizeof(map_info);
> +	int err;
> +
> +	err = bpf_obj_get_info_by_fd(attr_map_fd, &map_info, &map_info_len);
> +
> +	if (err)
> +		return false;
> +	return (map_info.key_size == sizeof(struct perf_event_attr)) &&
> +		(map_info.value_size == sizeof(struct perf_event_attr_map_entry));
> +}
> +
>  static int bperf_lock_attr_map(struct target *target)
>  {
>  	char path[PATH_MAX];
> @@ -342,7 +335,7 @@ static int bperf_lock_attr_map(struct target *target)
>  		scnprintf(path, PATH_MAX, "%s", target->attr_map);
>  	} else {
>  		scnprintf(path, PATH_MAX, "%s/%s", sysfs__mountpoint(),
> -			  DEFAULT_ATTR_MAP_PATH);
> +			  BPERF_DEFAULT_ATTR_MAP_PATH);
>  	}
>  
>  	if (access(path, F_OK)) {
> @@ -367,6 +360,11 @@ static int bperf_lock_attr_map(struct target *target)
>  			return -1;
>  	}
>  
> +	if (!bperf_attr_map_compatible(map_fd)) {
> +		close(map_fd);
> +		return -1;
> +
> +	}
>  	err = flock(map_fd, LOCK_EX);
>  	if (err) {
>  		close(map_fd);
> -- 
> 2.30.2
>