src/libbpf.c | 32 +++++++++++++++++++++++++------- 1 file changed, 25 insertions(+), 7 deletions(-)
libbpf looks for tracefs files only under debugfs, but tracefs may be
mounted even if debugfs is not. When /sys/kernel/debug/tracing is
absent, try looking under /sys/kernel/tracing instead.
Signed-off-by: Connor O'Brien <connoro@google.com>
---
v1->v2: cache result of debugfs check.
src/libbpf.c | 32 +++++++++++++++++++++++++-------
1 file changed, 25 insertions(+), 7 deletions(-)
diff --git a/src/libbpf.c b/src/libbpf.c
index 2262bcd..cc47c52 100644
--- a/src/libbpf.c
+++ b/src/libbpf.c
@@ -9945,10 +9945,22 @@ static void gen_kprobe_legacy_event_name(char *buf, size_t buf_sz,
__sync_fetch_and_add(&index, 1));
}
+static bool debugfs_available(void)
+{
+ static bool initialized = false, available;
+
+ if (!initialized) {
+ available = !access("/sys/kernel/debug/tracing", F_OK);
+ initialized = true;
+ }
+ return available;
+}
+
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";
+ const char *file = debugfs_available() ? "/sys/kernel/debug/tracing/kprobe_events" :
+ "/sys/kernel/tracing/kprobe_events";
return append_to_file(file, "%c:%s/%s %s+0x%zx",
retprobe ? 'r' : 'p',
@@ -9958,7 +9970,8 @@ 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";
+ const char *file = debugfs_available() ? "/sys/kernel/debug/tracing/kprobe_events" :
+ "/sys/kernel/tracing/kprobe_events";
return append_to_file(file, "-:%s/%s", retprobe ? "kretprobes" : "kprobes", probe_name);
}
@@ -9968,7 +9981,8 @@ static int determine_kprobe_perf_type_legacy(const char *probe_name, bool retpro
char file[256];
snprintf(file, sizeof(file),
- "/sys/kernel/debug/tracing/events/%s/%s/id",
+ debugfs_available() ? "/sys/kernel/debug/tracing/events/%s/%s/id" :
+ "/sys/kernel/tracing/events/%s/%s/id",
retprobe ? "kretprobes" : "kprobes", probe_name);
return parse_uint_from_file(file, "%d\n");
@@ -10144,7 +10158,8 @@ 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";
+ const char *file = debugfs_available() ? "/sys/kernel/debug/tracing/uprobe_events" :
+ "/sys/kernel/tracing/uprobe_events";
return append_to_file(file, "%c:%s/%s %s:0x%zx",
retprobe ? 'r' : 'p',
@@ -10154,7 +10169,8 @@ 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";
+ const char *file = debugfs_available() ? "/sys/kernel/debug/tracing/uprobe_events" :
+ "/sys/kernel/tracing/uprobe_events";
return append_to_file(file, "-:%s/%s", retprobe ? "uretprobes" : "uprobes", probe_name);
}
@@ -10164,7 +10180,8 @@ static int determine_uprobe_perf_type_legacy(const char *probe_name, bool retpro
char file[512];
snprintf(file, sizeof(file),
- "/sys/kernel/debug/tracing/events/%s/%s/id",
+ debugfs_available() ? "/sys/kernel/debug/tracing/events/%s/%s/id" :
+ "/sys/kernel/tracing/events/%s/%s/id",
retprobe ? "uretprobes" : "uprobes", probe_name);
return parse_uint_from_file(file, "%d\n");
@@ -10295,7 +10312,8 @@ static int determine_tracepoint_id(const char *tp_category,
int ret;
ret = snprintf(file, sizeof(file),
- "/sys/kernel/debug/tracing/events/%s/%s/id",
+ debugfs_available() ? "/sys/kernel/debug/tracing/events/%s/%s/id" :
+ "/sys/kernel/tracing/events/%s/%s/id",
tp_category, tp_name);
if (ret < 0)
return -errno;
--
2.36.1.124.g0e6072fb45-goog
On Mon, May 23, 2022 at 2:28 PM Connor O'Brien <connoro@google.com> wrote: > > libbpf looks for tracefs files only under debugfs, but tracefs may be > mounted even if debugfs is not. When /sys/kernel/debug/tracing is > absent, try looking under /sys/kernel/tracing instead. > > Signed-off-by: Connor O'Brien <connoro@google.com> > --- > v1->v2: cache result of debugfs check. > > src/libbpf.c | 32 +++++++++++++++++++++++++------- > 1 file changed, 25 insertions(+), 7 deletions(-) > > diff --git a/src/libbpf.c b/src/libbpf.c > index 2262bcd..cc47c52 100644 > --- a/src/libbpf.c > +++ b/src/libbpf.c > @@ -9945,10 +9945,22 @@ static void gen_kprobe_legacy_event_name(char *buf, size_t buf_sz, > __sync_fetch_and_add(&index, 1)); > } > > +static bool debugfs_available(void) > +{ > + static bool initialized = false, available; > + > + if (!initialized) { > + available = !access("/sys/kernel/debug/tracing", F_OK); > + initialized = true; > + } > + return available; > +} so thinking about this caching a bit, I'm not so sure we want to cache this decision. Mounting and unmounting of tracefs can happen after BPF application starts, so this debugfs_available flag can actually change while program is running. On the other hand, we don't do this check all that frequently, only during attach/detach, so it might be ok not to cache this result at all? WDYT? > + > 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"; > + const char *file = debugfs_available() ? "/sys/kernel/debug/tracing/kprobe_events" : > + "/sys/kernel/tracing/kprobe_events"; reading through this patch, it's now quite hard to see what differs, to be honest. While I do like full file path spelled out, now that we have two different prefixes it seems better to have prefixes separate. How about we do #define TRACEFS_PFX "/sys/kernel/tracing" #define DEBUGFS_PFX "/sys/kernel/debug/tracing" and then use that to construct strings. Like in the above example const char *file = has_debugfs() ? DEBUGFS_PFX "/kprobe_events" : TRACEFS_PFX "/kprobe_events"; and similarly below. That way at least we see clearly the part that's not dependent on debugfs/tracefs differences. > > return append_to_file(file, "%c:%s/%s %s+0x%zx", > retprobe ? 'r' : 'p', > @@ -9958,7 +9970,8 @@ 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"; > + const char *file = debugfs_available() ? "/sys/kernel/debug/tracing/kprobe_events" : > + "/sys/kernel/tracing/kprobe_events"; > > return append_to_file(file, "-:%s/%s", retprobe ? "kretprobes" : "kprobes", probe_name); > } > @@ -9968,7 +9981,8 @@ static int determine_kprobe_perf_type_legacy(const char *probe_name, bool retpro > char file[256]; > > snprintf(file, sizeof(file), > - "/sys/kernel/debug/tracing/events/%s/%s/id", > + debugfs_available() ? "/sys/kernel/debug/tracing/events/%s/%s/id" : > + "/sys/kernel/tracing/events/%s/%s/id", > retprobe ? "kretprobes" : "kprobes", probe_name); > > return parse_uint_from_file(file, "%d\n"); > @@ -10144,7 +10158,8 @@ 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"; > + const char *file = debugfs_available() ? "/sys/kernel/debug/tracing/uprobe_events" : > + "/sys/kernel/tracing/uprobe_events"; > > return append_to_file(file, "%c:%s/%s %s:0x%zx", > retprobe ? 'r' : 'p', > @@ -10154,7 +10169,8 @@ 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"; > + const char *file = debugfs_available() ? "/sys/kernel/debug/tracing/uprobe_events" : > + "/sys/kernel/tracing/uprobe_events"; > > return append_to_file(file, "-:%s/%s", retprobe ? "uretprobes" : "uprobes", probe_name); > } > @@ -10164,7 +10180,8 @@ static int determine_uprobe_perf_type_legacy(const char *probe_name, bool retpro > char file[512]; > > snprintf(file, sizeof(file), > - "/sys/kernel/debug/tracing/events/%s/%s/id", > + debugfs_available() ? "/sys/kernel/debug/tracing/events/%s/%s/id" : > + "/sys/kernel/tracing/events/%s/%s/id", like here, "events/%s/%s/id" is important to separate, so snprintf(file, sizeof(file), "%s/events/%s/%s/id", has_debugfs() ? DEBUGFS_PFX : TRACEFS_PFX, retprobe ? "uretprobes" : "uprobes", probe_name); seems easier to follow? > retprobe ? "uretprobes" : "uprobes", probe_name); > > return parse_uint_from_file(file, "%d\n"); > @@ -10295,7 +10312,8 @@ static int determine_tracepoint_id(const char *tp_category, > int ret; > > ret = snprintf(file, sizeof(file), > - "/sys/kernel/debug/tracing/events/%s/%s/id", > + debugfs_available() ? "/sys/kernel/debug/tracing/events/%s/%s/id" : > + "/sys/kernel/tracing/events/%s/%s/id", > tp_category, tp_name); > if (ret < 0) > return -errno; > -- > 2.36.1.124.g0e6072fb45-goog >
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