[PATCH v2 10/13] perf header: add a buffer to struct feat_fd

[David Carrillo-Cisneros <davidcc@google.com>]

Extend struct feat_fd to use a temporal buffer in pipe-mode, rather
than a perf.data file.

Revamp write_pmu_mappings to avoid seeking so that is compatible with
pipe-mode.

Print an error when trying to use buf in features that do not support
pipe-mode.

Signed-off-by: David Carrillo-Cisneros <davidcc@google.com>
---
 tools/perf/util/header.c | 79 +++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 62 insertions(+), 17 deletions(-)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 65cd2d1f1721..b7704b30ed52 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -60,6 +60,7 @@ struct perf_file_attr {
 struct feat_fd {
 	struct perf_header *ph;
 	int fd;
+	void *buf;	/* Either buf != NULL or fd >= 0 */
 	ssize_t offset;
 	size_t size;
 };
@@ -82,11 +83,27 @@ bool perf_header__has_feat(const struct perf_header *header, int feat)
 /* Return: 0 if succeded, -ERR if failed. */
 int do_write(struct feat_fd *fd, const void *buf, size_t size)
 {
-	ssize_t ret;
+	void *addr;
 
-	ret  = writen(fd->fd, buf, size);
-	if (ret != (ssize_t)size)
-		return ret < 0 ? (int)ret: -1;
+	if (!fd->buf) {
+		ssize_t ret = writen(fd->fd, buf, size);
+
+		if (ret != (ssize_t)size)
+			return ret < 0 ? (int)ret : -1;
+		return 0;
+	}
+retry:
+	if (size > (fd->size - fd->offset)) {
+		addr = realloc(fd->buf, fd->size << 1);
+		if (!addr)
+			return -ENOSPC;
+		fd->buf = addr;
+		fd->size <<= 1;
+		goto retry;
+	}
+
+	memcpy(fd->buf + fd->offset, buf, size);
+	fd->offset += size;
 
 	return 0;
 }
@@ -126,10 +143,21 @@ static int do_write_string(struct feat_fd *fd, const char *str)
 
 static int __do_read(struct feat_fd *fd, void *addr, ssize_t size)
 {
-	ssize_t ret = readn(fd->fd, addr, size);
+	if (!fd->buf) {
+		ssize_t ret = readn(fd->fd, addr, size);
+
+		if (ret != (ssize_t)size)
+			return ret < 0 ? (int)ret : -1;
+		return 0;
+	}
+
+	assert((ssize_t)fd->size > fd->offset);
+	if (size > (ssize_t)fd->size - fd->offset)
+		return -1;
+
+	memcpy(addr, fd->buf + fd->offset, size);
+	fd->offset += size;
 
-	if (ret != (ssize_t)size)
-		return ret < 0 ? (int)ret : -1;
 	return 0;
 }
 
@@ -187,6 +215,10 @@ static char *do_read_string(struct feat_fd *fd)
 static int write_tracing_data(struct feat_fd *fd,
 			      struct perf_evlist *evlist)
 {
+	if (fd->buf) {
+		pr_err("Unsupported write_tracing_data to memory buffer.\n");
+		return -1;
+	}
 	return read_tracing_data(fd->fd, &evlist->entries);
 }
 
@@ -201,6 +233,10 @@ static int write_build_id(struct feat_fd *fd,
 	if (!perf_session__read_build_ids(session, true))
 		return -1;
 
+	if (fd->buf) {
+		pr_err("Unsupported write_build_id to memory buffer.\n");
+		return -1;
+	}
 	err = perf_session__write_buildid_table(session, fd);
 	if (err < 0) {
 		pr_debug("failed to write buildid table\n");
@@ -795,11 +831,19 @@ static int write_pmu_mappings(struct feat_fd *fd,
 			      struct perf_evlist *evlist __maybe_unused)
 {
 	struct perf_pmu *pmu = NULL;
-	off_t offset = lseek(fd->fd, 0, SEEK_CUR);
-	__u32 pmu_num = 0;
+	u32 pmu_num = 0;
 	int ret;
 
-	/* write real pmu_num later */
+	/*
+	 * Do a first pass to count number of pmu to avoid lseek so this
+	 * works in pipe mode as well.
+	 */
+	while ((pmu = perf_pmu__scan(pmu))) {
+		if (!pmu->name)
+			continue;
+		pmu_num++;
+	}
+
 	ret = do_write(fd, &pmu_num, sizeof(pmu_num));
 	if (ret < 0)
 		return ret;
@@ -807,7 +851,6 @@ static int write_pmu_mappings(struct feat_fd *fd,
 	while ((pmu = perf_pmu__scan(pmu))) {
 		if (!pmu->name)
 			continue;
-		pmu_num++;
 
 		ret = do_write(fd, &pmu->type, sizeof(pmu->type));
 		if (ret < 0)
@@ -818,12 +861,6 @@ static int write_pmu_mappings(struct feat_fd *fd,
 			return ret;
 	}
 
-	if (pwrite(fd->fd, &pmu_num, sizeof(pmu_num), offset) != sizeof(pmu_num)) {
-		/* discard all */
-		lseek(fd->fd, offset, SEEK_SET);
-		return -1;
-	}
-
 	return 0;
 }
 
@@ -909,6 +946,10 @@ static int write_auxtrace(struct feat_fd *fd,
 	struct perf_session *session;
 	int err;
 
+	if (fd->buf) {
+		pr_err("Unsupported write_auxtrace to memory buffer.\n");
+		return -1;
+	}
 	session = container_of(fd->ph, struct perf_session, header);
 
 	err = auxtrace_index__write(fd->fd, &session->auxtrace_index);
@@ -2187,6 +2228,10 @@ static int do_write_feat(struct feat_fd *fd, struct perf_header *h, int type,
 		if (!feat_ops[type].write)
 			return -1;
 
+		if (fd->buf) {
+			pr_err("Called %s for memory buffer.\n", __func__);
+			return -1;
+		}
 		(*p)->offset = lseek(fd->fd, 0, SEEK_CUR);
 
 		err = feat_ops[type].write(fd, evlist);
-- 
2.13.0.219.gdb65acc882-goog