bzip2/lzma: remove nasty uncompressed size hack in pre-boot environment

decompress_bunzip2 and decompress_unlzma have a nasty hack that subtracts
4 from the input length if being called in the pre-boot environment.

This is a nasty hack because it relies on the fact that flush = NULL only
when called from the pre-boot environment (i.e.
arch/x86/boot/compressed/misc.c).  initramfs.c/do_mounts_rd.c pass in a
flush buffer (flush != NULL).

This hack prevents the decompressors from being used with flush = NULL by
other callers unless knowledge of the hack is propagated to them.

This patch removes the hack by making decompress (called only from the
pre-boot environment) a wrapper function that subtracts 4 from the input
length before calling the decompressor.

Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/decompress_bunzip2.c

@@ -45,9 +45,11 @@
 */
 
 
-#ifndef STATIC
+#ifdef STATIC
+#define PREBOOT
+#else
 #include <linux/decompress/bunzip2.h>
-#endif /* !STATIC */
+#endif /* STATIC */
 
 #include <linux/decompress/mm.h>
 #include <linux/slab.h>
@@ -681,9 +683,7 @@ STATIC int INIT bunzip2(unsigned char *buf, int len,
 	set_error_fn(error_fn);
 	if (flush)
 		outbuf = malloc(BZIP2_IOBUF_SIZE);
-	else
-		len -= 4; /* Uncompressed size hack active in pre-boot
-			     environment */
+
 	if (!outbuf) {
 		error("Could not allocate output bufer");
 		return -1;
@@ -733,4 +733,14 @@ exit_0:
 	return i;
 }
 
-#define decompress bunzip2
+#ifdef PREBOOT
+STATIC int INIT decompress(unsigned char *buf, int len,
+			int(*fill)(void*, unsigned int),
+			int(*flush)(void*, unsigned int),
+			unsigned char *outbuf,
+			int *pos,
+			void(*error_fn)(char *x))
+{
+	return bunzip2(buf, len - 4, fill, flush, outbuf, pos, error_fn);
+}
+#endif