strbuf: Do not append '\0' if not needed

Unconditionally appending '\0' is not a big problem, but that does
trigger the buffer to potentially be re-allocated. Avoid that by
checking the last char is not already NUL.

Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://github.com/kmod-project/kmod/pull/239

diff --git a/shared/strbuf.c b/shared/strbuf.c
index 5a25976c3b1408c71ec43230f5496b806f496312..69d20db6ec925d3432da2ba806e3426257f77d58 100644 (file)
--- a/shared/strbuf.c
+++ b/shared/strbuf.c
@@ -78,9 +78,11 @@ char *strbuf_steal(struct strbuf *buf)
 
 const char *strbuf_str(struct strbuf *buf)
 {
-       if (!strbuf_reserve_extra(buf, 1))
-               return NULL;
-       buf->bytes[buf->used] = '\0';
+       if (!buf->used || buf->bytes[buf->used - 1]) {
+               if (!strbuf_reserve_extra(buf, 1))
+                       return NULL;
+               buf->bytes[buf->used] = '\0';
+       }
        return buf->bytes;
 }