buffer: allow buffer truncation This is a similar idea to the POSIX truncate() function. It sets the used buffer size to a certain value. If the new size is larger than the old size, the newly visible bytes are zeroed out. If the new size is smaller than the old size, the bytes at the end are "lost" but the underlying buffer allocation remains unchanged. Signed-off-by: Josef 'Jeff' Sipek <jeffpc@josefsipek.net>

--- a/buffer_heap.c	Sat Jul 08 09:53:45 2017 +0300
+++ b/buffer_heap.c	Tue Jul 11 00:39:14 2017 +0300
@@ -25,5 +25,6 @@
 const struct buffer_ops heap_buffer = {
 	.realloc = realloc,
 	.free = free,
+	.clear = generic_buffer_clear_memset,
 	.copyin = generic_buffer_copyin_memcpy,
 };