[PATCHv2 RFC bpf-next 4/7] libbpf: Add btf__find_by_pattern_kind function

[Jiri Olsa <jolsa@kernel.org>]

Adding btf__find_by_pattern_kind function that returns
array of BTF ids for given function name pattern.

Using libc's regex.h support for that.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 tools/lib/bpf/btf.c | 68 +++++++++++++++++++++++++++++++++++++++++++++
 tools/lib/bpf/btf.h |  3 ++
 2 files changed, 71 insertions(+)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index d30e67e7e1e5..e193713b9d56 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
 /* Copyright (c) 2018 Facebook */
 
+#define _GNU_SOURCE
 #include <byteswap.h>
 #include <endian.h>
 #include <stdio.h>
@@ -16,6 +17,7 @@
 #include <linux/err.h>
 #include <linux/btf.h>
 #include <gelf.h>
+#include <regex.h>
 #include "btf.h"
 #include "bpf.h"
 #include "libbpf.h"
@@ -712,6 +714,72 @@ __s32 btf__find_by_name_kind(const struct btf *btf, const char *type_name,
 	return -ENOENT;
 }
 
+static bool is_wildcard(char c)
+{
+	static const char *wildchars = "*?[|";
+
+	return strchr(wildchars, c);
+}
+
+int btf__find_by_pattern_kind(const struct btf *btf,
+			      const char *type_pattern, __u32 kind,
+			      __s32 **__ids)
+{
+	__u32 i, nr_types = btf__get_nr_types(btf);
+	__s32 *ids = NULL;
+	int cnt = 0, alloc = 0, ret;
+	regex_t regex;
+	char *pattern;
+
+	if (kind == BTF_KIND_UNKN || !strcmp(type_pattern, "void"))
+		return 0;
+
+	/* When the pattern does not start with wildcard, treat it as
+	 * if we'd want to match it from the beginning of the string.
+	 */
+	asprintf(&pattern, "%s%s",
+		 is_wildcard(type_pattern[0]) ? "^" : "",
+		 type_pattern);
+
+	ret = regcomp(&regex, pattern, REG_EXTENDED);
+	if (ret) {
+		pr_warn("failed to compile regex\n");
+		free(pattern);
+		return -EINVAL;
+	}
+
+	free(pattern);
+
+	for (i = 1; i <= nr_types; i++) {
+		const struct btf_type *t = btf__type_by_id(btf, i);
+		const char *name;
+		__s32 *p;
+
+		if (btf_kind(t) != kind)
+			continue;
+		name = btf__name_by_offset(btf, t->name_off);
+		if (name && regexec(&regex, name, 0, NULL, 0))
+			continue;
+		if (cnt == alloc) {
+			alloc = max(100, alloc * 3 / 2);
+			p = realloc(ids, alloc * sizeof(__u32));
+			if (!p) {
+				free(ids);
+				regfree(&regex);
+				return -ENOMEM;
+			}
+			ids = p;
+		}
+
+		ids[cnt] = i;
+		cnt++;
+	}
+
+	regfree(&regex);
+	*__ids = ids;
+	return cnt ?: -ENOENT;
+}
+
 static bool btf_is_modifiable(const struct btf *btf)
 {
 	return (void *)btf->hdr != btf->raw_data;
diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
index b54f1c3ebd57..036857aded94 100644
--- a/tools/lib/bpf/btf.h
+++ b/tools/lib/bpf/btf.h
@@ -371,6 +371,9 @@ btf_var_secinfos(const struct btf_type *t)
 	return (struct btf_var_secinfo *)(t + 1);
 }
 
+int btf__find_by_pattern_kind(const struct btf *btf,
+			      const char *type_pattern, __u32 kind,
+			      __s32 **__ids);
 #ifdef __cplusplus
 } /* extern "C" */
 #endif
-- 
2.30.2