[PATCH 2/7] tracing: provide trace_seq_reserve()

[Eduard - Gabriel Munteanu]

trace_seq_reserve() allows a caller to reserve space in a trace_seq and
write directly into it. This makes it easier to export binary data to
userspace via the tracing interface, by simply filling in a struct.

Signed-off-by: Eduard - Gabriel Munteanu <eduard.munteanu@xxxxxxxxxxx>
---
 kernel/trace/trace_output.c |   13 +++++++++++++
 kernel/trace/trace_output.h |    1 +
 2 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 9fc8150..bdcc3fe 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -116,6 +116,19 @@ int trace_seq_putmem_hex(struct trace_seq *s, void *mem, size_t len)
 	return trace_seq_putmem(s, hex, j);
 }
 
+void *trace_seq_reserve(struct trace_seq *s, size_t len)
+{
+	void *ret;
+
+	if (len > ((PAGE_SIZE - 1) - s->len))
+		return NULL;
+
+	ret = s->buffer + s->len;
+	s->len += len;
+
+	return ret;
+}
+
 int trace_seq_path(struct trace_seq *s, struct path *path)
 {
 	unsigned char *p;
diff --git a/kernel/trace/trace_output.h b/kernel/trace/trace_output.h
index 551a25a..cbc0ec8 100644
--- a/kernel/trace/trace_output.h
+++ b/kernel/trace/trace_output.h
@@ -27,6 +27,7 @@ int trace_seq_puts(struct trace_seq *s, const char *str);
 int trace_seq_putc(struct trace_seq *s, unsigned char c);
 int trace_seq_putmem(struct trace_seq *s, void *mem, size_t len);
 int trace_seq_putmem_hex(struct trace_seq *s, void *mem, size_t len);
+void *trace_seq_reserve(struct trace_seq *s, size_t len);
 int trace_seq_path(struct trace_seq *s, struct path *path);
 int seq_print_userip_objs(const struct userstack_entry *entry,
 			  struct trace_seq *s, unsigned long sym_flags);
-- 
1.6.0.6

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