libbpf-tools: optimize fentry_exists helper

chenhengqi · yonghong-song · commit b2a76fa63f19 · 2021-06-10T09:29:27.000-07:00
The previous implementation checks fentry support either in vmlinux
or module BTF. So we need two calls to fentry_exists to verify that
whether a symbol exists. This commit updates this behavior to use
the module name provided as a hint, and fallback to vmlinux if module
BTF is not available.

Signed-off-by: Hengqi Chen &lt;chenhengqi@outlook.com&gt;
diff --git a/libbpf-tools/fsdist.c b/libbpf-tools/fsdist.c
@@ -230,8 +230,7 @@ static bool check_fentry()
 	for (i = 0; i < MAX_OP; i++) {
 		fn_name = fs_configs[fs_type].op_funcs[i];
 		module = fs_configs[fs_type].fs;
-		if (fn_name && !fentry_exists(fn_name, NULL)
-		    && !fentry_exists(fn_name, module)) {
+		if (fn_name && !fentry_exists(fn_name, module)) {
 			support_fentry = false;
 			break;
 		}
diff --git a/libbpf-tools/fsslower.c b/libbpf-tools/fsslower.c
@@ -202,8 +202,7 @@ static bool check_fentry()
 	for (i = 0; i < MAX_OP; i++) {
 		fn_name = fs_configs[fs_type].op_funcs[i];
 		module = fs_configs[fs_type].fs;
-		if (fn_name && !fentry_exists(fn_name, NULL)
-		    && !fentry_exists(fn_name, module)) {
+		if (fn_name && !fentry_exists(fn_name, module)) {
 			support_fentry = false;
 			break;
 		}
diff --git a/libbpf-tools/trace_helpers.c b/libbpf-tools/trace_helpers.c
@@ -1013,16 +1013,18 @@ bool fentry_exists(const char *name, const char *mod)
 			sysfs_vmlinux, strerror(-libbpf_get_error(base)));
 		goto err_out;
 	}
-	if (mod) {
+	if (mod && module_btf_exists(mod)) {
 		snprintf(sysfs_mod, sizeof(sysfs_mod), "/sys/kernel/btf/%s", mod);
 		btf = btf__parse_split(sysfs_mod, base);
 		if (libbpf_get_error(btf)) {
 			fprintf(stderr, "failed to load BTF from %s: %s\n",
 				sysfs_mod, strerror(-libbpf_get_error(btf)));
-			goto err_out;
+			btf = base;
+			base = NULL;
 		}
 	} else {
 		btf = base;
+		base = NULL;
 	}
 
 	id = btf__find_by_name_kind(btf, "bpf_attach_type", BTF_KIND_ENUM);
@@ -1044,8 +1046,7 @@ bool fentry_exists(const char *name, const char *mod)
 	}
 
 err_out:
-	if (mod)
-		btf__free(btf);
+	btf__free(btf);
 	btf__free(base);
 	return id > 0;
 }
diff --git a/libbpf-tools/trace_helpers.h b/libbpf-tools/trace_helpers.h
@@ -75,8 +75,8 @@ bool is_kernel_module(const char *name);
  *
  * *name* is the name of a kernel function to be attached to, which can be
  * from vmlinux or a kernel module.
- * *mod* is the name of a kernel module, if NULL, it means *name*
- * belongs to vmlinux.
+ * *mod* is a hint that indicates the *name* may reside in module BTF,
+ * if NULL, it means *name* belongs to vmlinux.
  */
 bool fentry_exists(const char *name, const char *mod);
 

Original file line number	Diff line number	Diff line change
`@@ -1013,16 +1013,18 @@ bool fentry_exists(const char name, const char mod)`
`1013`	`1013`	`sysfs_vmlinux, strerror(-libbpf_get_error(base)));`
`1014`	`1014`	`goto err_out;`
`1015`	`1015`	`}`
`1016`		`- if (mod) {`
	`1016`	`+ if (mod && module_btf_exists(mod)) {`
`1017`	`1017`	`snprintf(sysfs_mod, sizeof(sysfs_mod), "/sys/kernel/btf/%s", mod);`
`1018`	`1018`	`btf = btf__parse_split(sysfs_mod, base);`
`1019`	`1019`	`if (libbpf_get_error(btf)) {`
`1020`	`1020`	`fprintf(stderr, "failed to load BTF from %s: %s\n",`
`1021`	`1021`	`sysfs_mod, strerror(-libbpf_get_error(btf)));`
`1022`		`- goto err_out;`
	`1022`	`+ btf = base;`
	`1023`	`+ base = NULL;`
`1023`	`1024`	`}`
`1024`	`1025`	`} else {`
`1025`	`1026`	`btf = base;`
	`1027`	`+ base = NULL;`
`1026`	`1028`	`}`
`1027`	`1029`
`1028`	`1030`	`id = btf__find_by_name_kind(btf, "bpf_attach_type", BTF_KIND_ENUM);`
`@@ -1044,8 +1046,7 @@ bool fentry_exists(const char name, const char mod)`
`1044`	`1046`	`}`
`1045`	`1047`
`1046`	`1048`	`err_out:`
`1047`		`- if (mod)`
`1048`		`- btf__free(btf);`
	`1049`	`+ btf__free(btf);`
`1049`	`1050`	`btf__free(base);`
`1050`	`1051`	`return id > 0;`
`1051`	`1052`	`}`