btf_encoder: Rework btf_encoders__*() API to allow traversal of encoders

To coordinate across multiple encoders at collection time, there will be
a need to access the set of encoders.  Rework the unused
btf_encoders__*() API to facilitate this.

Committer notes:

Removed btf_encoders__for_each_encoder() duplicate define, pointed out
by Jiri Olsa.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Tested-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Hao Luo <haoluo@google.com>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: KP Singh <kpsingh@chromium.org>
Cc: Kui-Feng Lee <sinquersw@gmail.com>
Cc: Martin KaFai Lau <martin.lau@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Stanislav Fomichev <sdf@google.com>
Cc: Timo Beckers <timo@incline.eu>
Cc: Yonghong Song <yhs@fb.com>
Cc: bpf@vger.kernel.org
Link: https://lore.kernel.org/r/1675790102-23037-5-git-send-email-alan.maguire@oracle.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

2 files changed, 28 insertions, 14 deletions

diff --git a/btf_encoder.c b/btf_encoder.c
index 71f67ae5..74ab61b0 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -30,6 +30,7 @@
 
 #include <errno.h>
 #include <stdint.h>
+#include <pthread.h>
 
 struct elf_function {
 	const char	*name;
@@ -79,19 +80,36 @@ struct btf_encoder {
 	} functions;
 };
 
-void btf_encoders__add(struct list_head *encoders, struct btf_encoder *encoder)
-{
-	list_add_tail(&encoder->node, encoders);
-}
+static LIST_HEAD(encoders);
+static pthread_mutex_t encoders__lock = PTHREAD_MUTEX_INITIALIZER;
+
+/* mutex only needed for add/delete, as this can happen in multiple encoding
+ * threads.  Traversal of the list is currently confined to thread collection.
+ */
 
-struct btf_encoder *btf_encoders__first(struct list_head *encoders)
+#define btf_encoders__for_each_encoder(encoder)		\
+	list_for_each_entry(encoder, &encoders, node)
+
+static void btf_encoders__add(struct btf_encoder *encoder)
 {
-	return list_first_entry(encoders, struct btf_encoder, node);
+	pthread_mutex_lock(&encoders__lock);
+	list_add_tail(&encoder->node, &encoders);
+	pthread_mutex_unlock(&encoders__lock);
 }
 
-struct btf_encoder *btf_encoders__next(struct btf_encoder *encoder)
+static void btf_encoders__delete(struct btf_encoder *encoder)
 {
-	return list_next_entry(encoder, node);
+	struct btf_encoder *existing = NULL;
+
+	pthread_mutex_lock(&encoders__lock);
+	/* encoder may not have been added to list yet; check. */
+	btf_encoders__for_each_encoder(existing) {
+		if (encoder == existing)
+			break;
+	}
+	if (encoder == existing)
+		list_del(&encoder->node);
+	pthread_mutex_unlock(&encoders__lock);
 }
 
 #define PERCPU_SECTION ".data..percpu"
@@ -1505,6 +1523,7 @@ struct btf_encoder *btf_encoder__new(struct cu *cu, const char *detached_filenam
 
 		if (encoder->verbose)
 			printf("File %s:\n", cu->filename);
+		btf_encoders__add(encoder);
 	}
 out:
 	return encoder;
@@ -1519,6 +1538,7 @@ void btf_encoder__delete(struct btf_encoder *encoder)
 	if (encoder == NULL)
 		return;
 
+	btf_encoders__delete(encoder);
 	__gobuffer__delete(&encoder->percpu_secinfo);
 	zfree(&encoder->filename);
 	btf__free(encoder->btf);
diff --git a/btf_encoder.h b/btf_encoder.h
index a65120cc..34516bb1 100644
--- a/btf_encoder.h
+++ b/btf_encoder.h
@@ -23,12 +23,6 @@ int btf_encoder__encode(struct btf_encoder *encoder);
 
 int btf_encoder__encode_cu(struct btf_encoder *encoder, struct cu *cu, struct conf_load *conf_load);
 
-void btf_encoders__add(struct list_head *encoders, struct btf_encoder *encoder);
-
-struct btf_encoder *btf_encoders__first(struct list_head *encoders);
-
-struct btf_encoder *btf_encoders__next(struct btf_encoder *encoder);
-
 struct btf *btf_encoder__btf(struct btf_encoder *encoder);
 
 int btf_encoder__add_encoder(struct btf_encoder *encoder, struct btf_encoder *other);