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native/src/core/bootstages.cpp

@@ -62,6 +62,11 @@ static void mount_mirrors() {
 
     // Check and mount preinit mirror
     if (struct stat st{}; stat((MAGISKTMP + "/" PREINITDEV).data(), &st) == 0 && (st.st_mode & S_IFBLK)) {
+        // DO NOT mount the block device directly, as we do not know the flags and configs
+        // to properly mount the partition; mounting block devices directly as rw could cause
+        // crashes if the filesystem driver is crap (e.g. some broken F2FS drivers).
+        // What we do instead is to scan through the current mountinfo and find a pre-existing
+        // mount point mounting our desired partition, and then bind mount the target folder.
         dev_t preinit_dev = st.st_rdev;
         for (const auto &info: self_mount_info) {
             if (info.root == "/" && info.device == preinit_dev) {

native/src/init/mount.cpp

@@ -129,6 +129,10 @@ static void mount_preinit_dir(string path, dev_t preinit_dev) {
         }
     }
 
+    // Since we are mounting the block device directly, make sure to ONLY mount the partitions
+    // as read-only, or else the kernel might crash due to crappy drivers.
+    // After the device boots up, magiskd will properly bind mount the correct partition
+    // on to PREINITMIRR as writable. For more details, check bootstages.cpp
     if (mounted || mount(PREINITDEV, PREINITMNT, "ext4", MS_RDONLY, nullptr) == 0 ||
         mount(PREINITDEV, PREINITMNT, "f2fs", MS_RDONLY, nullptr) == 0) {
         string preinit_dir = resolve_preinit_dir(PREINITMNT);