Commit a1ac9fd6 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
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libbpf: fallback to tracefs mount point if debugfs is not mounted 



Teach libbpf to fallback to tracefs mount point (/sys/kernel/tracing) if
debugfs (/sys/kernel/debug/tracing) isn't mounted.

Acked-by: default avatarYonghong Song <yhs@fb.com>
Suggested-by: default avatarConnor O'Brien <connoro@google.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20220715185736.898848-1-andrii@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent fd189422

tools/lib/bpf/libbpf.c

+40 −21
Original line number Diff line number Diff line
@@ -9864,6 +9864,34 @@ static int append_to_file(const char *file, const char *fmt, ...) 
	return err;

}



#define DEBUGFS "/sys/kernel/debug/tracing"

#define TRACEFS "/sys/kernel/tracing"



static bool use_debugfs(void)

{

	static int has_debugfs = -1;



	if (has_debugfs < 0)

		has_debugfs = access(DEBUGFS, F_OK) == 0;



	return has_debugfs == 1;

}



static const char *tracefs_path(void)

{

	return use_debugfs() ? DEBUGFS : TRACEFS;

}



static const char *tracefs_kprobe_events(void)

{

	return use_debugfs() ? DEBUGFS"/kprobe_events" : TRACEFS"/kprobe_events";

}



static const char *tracefs_uprobe_events(void)

{

	return use_debugfs() ? DEBUGFS"/uprobe_events" : TRACEFS"/uprobe_events";

}



static void gen_kprobe_legacy_event_name(char *buf, size_t buf_sz,

					 const char *kfunc_name, size_t offset)

{
@@ -9876,9 +9904,7 @@ static void gen_kprobe_legacy_event_name(char *buf, size_t buf_sz, 
static int add_kprobe_event_legacy(const char *probe_name, bool retprobe,

				   const char *kfunc_name, size_t offset)

{

	const char *file = "/sys/kernel/debug/tracing/kprobe_events";



	return append_to_file(file, "%c:%s/%s %s+0x%zx",

	return append_to_file(tracefs_kprobe_events(), "%c:%s/%s %s+0x%zx",

			      retprobe ? 'r' : 'p',

			      retprobe ? "kretprobes" : "kprobes",

			      probe_name, kfunc_name, offset);
@@ -9886,18 +9912,16 @@ static int add_kprobe_event_legacy(const char *probe_name, bool retprobe, 


static int remove_kprobe_event_legacy(const char *probe_name, bool retprobe)

{

	const char *file = "/sys/kernel/debug/tracing/kprobe_events";



	return append_to_file(file, "-:%s/%s", retprobe ? "kretprobes" : "kprobes", probe_name);

	return append_to_file(tracefs_kprobe_events(), "-:%s/%s",

			      retprobe ? "kretprobes" : "kprobes", probe_name);

}



static int determine_kprobe_perf_type_legacy(const char *probe_name, bool retprobe)

{

	char file[256];



	snprintf(file, sizeof(file),

		 "/sys/kernel/debug/tracing/events/%s/%s/id",

		 retprobe ? "kretprobes" : "kprobes", probe_name);

	snprintf(file, sizeof(file), "%s/events/%s/%s/id",

		 tracefs_path(), retprobe ? "kretprobes" : "kprobes", probe_name);



	return parse_uint_from_file(file, "%d\n");

}
@@ -10347,9 +10371,7 @@ static void gen_uprobe_legacy_event_name(char *buf, size_t buf_sz, 
static inline int add_uprobe_event_legacy(const char *probe_name, bool retprobe,

					  const char *binary_path, size_t offset)

{

	const char *file = "/sys/kernel/debug/tracing/uprobe_events";



	return append_to_file(file, "%c:%s/%s %s:0x%zx",

	return append_to_file(tracefs_uprobe_events(), "%c:%s/%s %s:0x%zx",

			      retprobe ? 'r' : 'p',

			      retprobe ? "uretprobes" : "uprobes",

			      probe_name, binary_path, offset);
@@ -10357,18 +10379,16 @@ static inline int add_uprobe_event_legacy(const char *probe_name, bool retprobe, 


static inline int remove_uprobe_event_legacy(const char *probe_name, bool retprobe)

{

	const char *file = "/sys/kernel/debug/tracing/uprobe_events";



	return append_to_file(file, "-:%s/%s", retprobe ? "uretprobes" : "uprobes", probe_name);

	return append_to_file(tracefs_uprobe_events(), "-:%s/%s",

			      retprobe ? "uretprobes" : "uprobes", probe_name);

}



static int determine_uprobe_perf_type_legacy(const char *probe_name, bool retprobe)

{

	char file[512];



	snprintf(file, sizeof(file),

		 "/sys/kernel/debug/tracing/events/%s/%s/id",

		 retprobe ? "uretprobes" : "uprobes", probe_name);

	snprintf(file, sizeof(file), "%s/events/%s/%s/id",

		 tracefs_path(), retprobe ? "uretprobes" : "uprobes", probe_name);



	return parse_uint_from_file(file, "%d\n");

}
@@ -10916,9 +10936,8 @@ static int determine_tracepoint_id(const char *tp_category, 
	char file[PATH_MAX];

	int ret;



	ret = snprintf(file, sizeof(file),

		       "/sys/kernel/debug/tracing/events/%s/%s/id",

		       tp_category, tp_name);

	ret = snprintf(file, sizeof(file), "%s/events/%s/%s/id",

		       tracefs_path(), tp_category, tp_name);

	if (ret < 0)

		return -errno;

	if (ret >= sizeof(file)) {