Commit 189a977e authored by Namhyung Kim's avatar Namhyung Kim
Browse files

perf bpf-filter: Improve error messages 



The BPF filter needs libbpf/BPF-skeleton support and root privilege.
Add error messages to help users understand the problem easily.

When it's not build with BPF support (make BUILD_BPF_SKEL=0).

  $ sudo perf record -e cycles --filter "pid != 0" true
  Error: BPF filter is requested but perf is not built with BPF.
  	Please make sure to build with libbpf and BPF skeleton.

   Usage: perf record [<options>] [<command>]
      or: perf record [<options>] -- <command> [<options>]

          --filter <filter>
                            event filter

When it supports BPF but runs without root or CAP_BPF.  Note that it
also checks pinned BPF filters.

  $ perf record -e cycles --filter "pid != 0" -o /dev/null true
  Error: BPF filter only works for users with the CAP_BPF capability!
  	Please run 'perf record --setup-filter pin' as root first.

   Usage: perf record [<options>] [<command>]
      or: perf record [<options>] -- <command> [<options>]

          --filter <filter>
                            event filter

Reviewed-by: default avatarIan Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250604174835.1852481-1-namhyung@kernel.org


Signed-off-by: default avatarNamhyung Kim <namhyung@kernel.org>
parent 19272b37

tools/perf/util/bpf-filter.c

+28 −0
Original line number Diff line number Diff line
@@ -52,6 +52,7 @@ 
#include <internal/xyarray.h>

#include <perf/threadmap.h>



#include "util/cap.h"

#include "util/debug.h"

#include "util/evsel.h"

#include "util/target.h"
@@ -618,11 +619,38 @@ struct perf_bpf_filter_expr *perf_bpf_filter_expr__new(enum perf_bpf_filter_term 
	return expr;

}



static bool check_bpf_filter_capable(void)

{

	bool used_root;



	if (perf_cap__capable(CAP_BPF, &used_root))

		return true;



	if (!used_root) {

		/* Check if root already pinned the filter programs and maps */

		int fd = get_pinned_fd("filters");



		if (fd >= 0) {

			close(fd);

			return true;

		}

	}



	pr_err("Error: BPF filter only works for %s!\n"

	       "\tPlease run 'perf record --setup-filter pin' as root first.\n",

	       used_root ? "root" : "users with the CAP_BPF capability");



	return false;

}



int perf_bpf_filter__parse(struct list_head *expr_head, const char *str)

{

	YY_BUFFER_STATE buffer;

	int ret;



	if (!check_bpf_filter_capable())

		return -EPERM;



	buffer = perf_bpf_filter__scan_string(str);



	ret = perf_bpf_filter_parse(expr_head);

tools/perf/util/bpf-filter.h

+3 −0
Original line number Diff line number Diff line
@@ -5,6 +5,7 @@ 
#include <linux/list.h>



#include "bpf_skel/sample-filter.h"

#include "util/debug.h"



struct perf_bpf_filter_expr {

	struct list_head list;
@@ -38,6 +39,8 @@ int perf_bpf_filter__unpin(void); 
static inline int perf_bpf_filter__parse(struct list_head *expr_head __maybe_unused,

					 const char *str __maybe_unused)

{

	pr_err("Error: BPF filter is requested but perf is not built with BPF.\n"

		"\tPlease make sure to build with libbpf and BPF skeleton.\n");

	return -EOPNOTSUPP;

}

static inline int perf_bpf_filter__prepare(struct evsel *evsel __maybe_unused,

tools/perf/util/cap.c

+0 −1
Original line number Diff line number Diff line
@@ -7,7 +7,6 @@ 
#include "debug.h"

#include <errno.h>

#include <string.h>

#include <linux/capability.h>

#include <sys/syscall.h>

#include <unistd.h>

tools/perf/util/cap.h

+5 −0
Original line number Diff line number Diff line
@@ -3,6 +3,7 @@ 
#define __PERF_CAP_H



#include <stdbool.h>

#include <linux/capability.h>



/* For older systems */

#ifndef CAP_SYSLOG
@@ -13,6 +14,10 @@ 
#define CAP_PERFMON	38

#endif



#ifndef CAP_BPF

#define CAP_BPF		39

#endif



/* Query if a capability is supported, used_root is set if the fallback root check was used. */

bool perf_cap__capable(int cap, bool *used_root);