initramfs: add write error checks

On a system with low memory extracting the initramfs may fail.  If this
happens the user gets "Failed to execute /init" instead of an initramfs
error.

Check return value of sys_write and call error() when the write was
incomplete or failed.
Signed-off-by: NDavid Engraf <david.engraf@sysgo.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

init/initramfs.c

@@ -369,7 +369,8 @@ static int __init do_name(void)
 static int __init do_copy(void)
 {
 	if (count >= body_len) {
-		xwrite(wfd, victim, body_len);
+		if (xwrite(wfd, victim, body_len) != body_len)
+			error("write error");
 		sys_close(wfd);
 		do_utime(vcollected, mtime);
 		kfree(vcollected);
@@ -377,7 +378,8 @@ static int __init do_copy(void)
 		state = SkipIt;
 		return 0;
 	} else {
-		xwrite(wfd, victim, count);
+		if (xwrite(wfd, victim, count) != count)
+			error("write error");
 		body_len -= count;
 		eat(count);
 		return 1;