tracing: provide trace_seq_reserve()

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@linux360.ro>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 19261fdd245581c42f1912b50febc03f5b9164a9..6595074cbac5ed7b268b43eba3e46b7285e58613 100644 (file)
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -167,6 +167,19 @@ 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 35c422fb51a93274cc81127b5f760c1af4d49eb8..0ae20b83eec8166607143dcd28f6f790403c1622 100644 (file)
--- a/kernel/trace/trace_output.h
+++ b/kernel/trace/trace_output.h
@@ -33,6 +33,7 @@ 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);