util: add ability to release a last piece from a shared pool (v2)

v2: s/shfree/shfree_last
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/util.h

@@ -319,5 +319,6 @@ static inline int read_img_str(int fd, char **pstr, int size)
 }
 
 extern void *shmalloc(size_t bytes);
+extern void shfree_last(void *ptr);
 
 #endif /* UTIL_H_ */

util.c

@@ -297,6 +297,7 @@ int is_anon_link_type(int lfd, char *type)
 
 static void *sh_buf;
 static unsigned int sh_bytes_left;
+static size_t sh_last_size;
 #define SH_BUF_CHUNK	4096
 
 void *shmalloc(size_t bytes)
@@ -322,6 +323,16 @@ void *shmalloc(size_t bytes)
 	ret = sh_buf;
 	sh_buf += bytes;
 	sh_bytes_left -= bytes;
+	sh_last_size = bytes;
 
 	return ret;
 }
+
+/* Only last chunk can be released */
+void shfree_last(void *ptr)
+{
+	BUG_ON(sh_buf - sh_last_size != ptr);
+	sh_buf -= sh_last_size;
+	sh_bytes_left += sh_last_size;
+	sh_last_size = 0;
+}