openbsd-ext4/writeup/3.md

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# Mount source code
Let's look at OpenBSD's mounting, as present in `ext2fs_vfsops.c`.
The first two function declarations prove quite useful:
```c
int ext2fs_sbupdate(struct ufsmount *, int);
static int e2fs_sbcheck(struct ext2fs *, int);
```
The first thing we are concerned with, of course, is the super block. With that being said, let's keep reading.
Below that, we have a struct called `ext2fs_vfsops` which just contains values that are defined as certain constants (e.g. `.vfs_mount = ext2fs_mount`), but we don't care about that. Then we have the inode pool, the `ext2gennumber`, and below that, we have the initializer of the inode pool, which probably needs to be tweaked for 64-bit as well. No wonder nobody has done it 😅
At this point, we should see where in the mounting process ext4 fails. Create an ext4 filesystem using qemu and mount it; make sure that the virtual machine manager marks it as a readonly filesystem before mounting it to ensure that it doesn't get corrupted (at least, not yet).