From 1283167595270b848df5d954fb41fa8daf46de23 Mon Sep 17 00:00:00 2001
From: topjohnwu <topjohnwu@gmail.com>
Date: Sat, 7 Jul 2018 01:32:58 +0800
Subject: [PATCH] Maintain our own set of loop devices

---
 native/jni/core/bootstages.c |  1 +
 native/jni/include/magisk.h  |  1 +
 native/jni/utils/img.c       | 41 ++++++++++++++++++++++++++----------
 3 files changed, 32 insertions(+), 11 deletions(-)

diff --git a/native/jni/core/bootstages.c b/native/jni/core/bootstages.c
index 85cae46da..c714d81c5 100644
--- a/native/jni/core/bootstages.c
+++ b/native/jni/core/bootstages.c
@@ -612,6 +612,7 @@ void startup() {
 	xmkdir(MIRRDIR "/bin", 0755);
 	xmkdir(BBPATH, 0755);
 	xmkdir(MOUNTPOINT, 0755);
+	xmkdir(BLOCKDIR, 0755);
 
 	LOGI("* Mounting mirrors");
 	struct vector mounts;
diff --git a/native/jni/include/magisk.h b/native/jni/include/magisk.h
index ff6f428f1..10e418f18 100644
--- a/native/jni/include/magisk.h
+++ b/native/jni/include/magisk.h
@@ -19,6 +19,7 @@
 #define UNBLOCKFILE     "/dev/.magisk.unblock"
 #define DISABLEFILE     "/cache/.disable_magisk"
 #define MAGISKTMP       "/sbin/.core"
+#define BLOCKDIR        MAGISKTMP "/block"
 #define MIRRDIR         MAGISKTMP "/mirror"
 #define BBPATH          MAGISKTMP "/busybox"
 #define MOUNTPOINT      MAGISKTMP "/img"
diff --git a/native/jni/utils/img.c b/native/jni/utils/img.c
index a35c0dff1..9d7673e93 100644
--- a/native/jni/utils/img.c
+++ b/native/jni/utils/img.c
@@ -9,6 +9,7 @@
 #include <sys/mount.h>
 #include <sys/sendfile.h>
 #include <sys/statvfs.h>
+#include <sys/sysmacros.h>
 #include <linux/loop.h>
 
 #include "magisk.h"
@@ -26,23 +27,41 @@ struct fs_info {
 };
 
 static char *loopsetup(const char *img) {
-	char device[20];
+	char device[32];
 	struct loop_info64 info;
-	int i, lfd, ffd;
+	int lfd = -1, ffd;
 	memset(&info, 0, sizeof(info));
-	// First get an empty loop device
-	for (i = 0; i <= 7; ++i) {
-		sprintf(device, "/dev/block/loop%d", i);
-		lfd = xopen(device, O_RDWR);
-		if (ioctl(lfd, LOOP_GET_STATUS64, &info) == -1)
-			break;
-		close(lfd);
+	if (access(BLOCKDIR, F_OK) == 0) {
+		for (int i = 8; i < 100; ++i) {
+			sprintf(device, BLOCKDIR "/loop%02d", i);
+			if (access(device, F_OK) != 0)
+				mknod(device, S_IFBLK | 0600, makedev(7, i * 8));
+			lfd = open(device, O_RDWR);
+			if (lfd < 0) /* Kernel does not support this */
+				break;
+			if (ioctl(lfd, LOOP_GET_STATUS64, &info) == -1)
+				break;
+			close(lfd);
+			lfd = -1;
+		}
 	}
-	if (i == 8) return NULL;
+	// Fallback to existing loop in dev, but in reverse order
+	if (lfd < 0) {
+		for (int i = 7; i >= 0; --i) {
+			sprintf(device, "/dev/block/loop%d", i);
+			lfd = xopen(device, O_RDWR);
+			if (ioctl(lfd, LOOP_GET_STATUS64, &info) == -1)
+				break;
+			close(lfd);
+			lfd = -1;
+		}
+	}
+	if (lfd < 0)
+		return NULL;
 	ffd = xopen(img, O_RDWR);
 	if (ioctl(lfd, LOOP_SET_FD, ffd) == -1)
 		return NULL;
-	strcpy((char *) info.lo_file_name, img);
+	strncpy((char *) info.lo_file_name, img, sizeof(info.lo_file_name));
 	ioctl(lfd, LOOP_SET_STATUS64, &info);
 	close(lfd);
 	close(ffd);