perf header: Add ability to keep feature sections

Many feature sections should not be re-written during perf inject. In
preparation to support that, add callbacks that a tool can use to copy
a feature section from elsewhere. perf inject will use this facility to
copy features sections from the input file.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20220520132404.25853-2-adrian.hunter@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/header.c

@@ -3462,9 +3462,22 @@ int perf_header__fprintf_info(struct perf_session *session, FILE *fp, bool full)
 	return 0;
 }
 
+struct header_fw {
+	struct feat_writer	fw;
+	struct feat_fd		*ff;
+};
+
+static int feat_writer_cb(struct feat_writer *fw, void *buf, size_t sz)
+{
+	struct header_fw *h = container_of(fw, struct header_fw, fw);
+
+	return do_write(h->ff, buf, sz);
+}
+
 static int do_write_feat(struct feat_fd *ff, int type,
 			 struct perf_file_section **p,
-			 struct evlist *evlist)
+			 struct evlist *evlist,
+			 struct feat_copier *fc)
 {
 	int err;
 	int ret = 0;
@@ -3478,7 +3491,23 @@ static int do_write_feat(struct feat_fd *ff, int type,
 
 		(*p)->offset = lseek(ff->fd, 0, SEEK_CUR);
 
-		err = feat_ops[type].write(ff, evlist);
+		/*
+		 * Hook to let perf inject copy features sections from the input
+		 * file.
+		 */
+		if (fc && fc->copy) {
+			struct header_fw h = {
+				.fw.write = feat_writer_cb,
+				.ff = ff,
+			};
+
+			/* ->copy() returns 0 if the feature was not copied */
+			err = fc->copy(fc, type, &h.fw);
+		} else {
+			err = 0;
+		}
+		if (!err)
+			err = feat_ops[type].write(ff, evlist);
 		if (err < 0) {
 			pr_debug("failed to write feature %s\n", feat_ops[type].name);
 
@@ -3494,7 +3523,8 @@ static int do_write_feat(struct feat_fd *ff, int type,
 }
 
 static int perf_header__adds_write(struct perf_header *header,
-				   struct evlist *evlist, int fd)
+				   struct evlist *evlist, int fd,
+				   struct feat_copier *fc)
 {
 	int nr_sections;
 	struct feat_fd ff;
@@ -3523,7 +3553,7 @@ static int perf_header__adds_write(struct perf_header *header,
 	lseek(fd, sec_start + sec_size, SEEK_SET);
 
 	for_each_set_bit(feat, header->adds_features, HEADER_FEAT_BITS) {
-		if (do_write_feat(&ff, feat, &p, evlist))
+		if (do_write_feat(&ff, feat, &p, evlist, fc))
 			perf_header__clear_feat(header, feat);
 	}
 
@@ -3561,9 +3591,10 @@ int perf_header__write_pipe(int fd)
 	return 0;
 }
 
-int perf_session__write_header(struct perf_session *session,
-			       struct evlist *evlist,
-			       int fd, bool at_exit)
+static int perf_session__do_write_header(struct perf_session *session,
+					 struct evlist *evlist,
+					 int fd, bool at_exit,
+					 struct feat_copier *fc)
 {
 	struct perf_file_header f_header;
 	struct perf_file_attr   f_attr;
@@ -3615,7 +3646,7 @@ int perf_session__write_header(struct perf_session *session,
 	header->feat_offset = header->data_offset + header->data_size;
 
 	if (at_exit) {
-		err = perf_header__adds_write(header, evlist, fd);
+		err = perf_header__adds_write(header, evlist, fd, fc);
 		if (err < 0)
 			return err;
 	}
@@ -3648,6 +3679,13 @@ int perf_session__write_header(struct perf_session *session,
 	return 0;
 }
 
+int perf_session__write_header(struct perf_session *session,
+			       struct evlist *evlist,
+			       int fd, bool at_exit)
+{
+	return perf_session__do_write_header(session, evlist, fd, at_exit, NULL);
+}
+
 static int perf_header__getbuffer64(struct perf_header *header,
 				    int fd, void *buf, size_t size)
 {

tools/perf/util/header.h

@@ -121,6 +121,16 @@ int perf_session__write_header(struct perf_session *session,
 			       int fd, bool at_exit);
 int perf_header__write_pipe(int fd);
 
+/* feat_writer writes a feature section to output */
+struct feat_writer {
+	int (*write)(struct feat_writer *fw, void *buf, size_t sz);
+};
+
+/* feat_copier copies a feature section using feat_writer to output */
+struct feat_copier {
+	int (*copy)(struct feat_copier *fc, int feat, struct feat_writer *fw);
+};
+
 void perf_header__set_feat(struct perf_header *header, int feat);
 void perf_header__clear_feat(struct perf_header *header, int feat);
 bool perf_header__has_feat(const struct perf_header *header, int feat);