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added starting to look in the mounting calls etc

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Om Raheja 2024-08-17 19:21:36 -04:00
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commit b11bfe8ed6
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11
writeup/2.md
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@ -58,4 +58,15 @@ int ext2fs_sysctl(int *, u_int, void *, size_t *, void *, size_t,
Here we have some information regarding mounts. Obviously, this is the first thing we need to implement. We can try to mount a 64-bit filesystem successfully and having errors on every read first, and then slowly break our way out of that. Here we have some information regarding mounts. Obviously, this is the first thing we need to implement. We can try to mount a 64-bit filesystem successfully and having errors on every read first, and then slowly break our way out of that.
```c
/* ext2fs_readwrite.c */
int ext2fs_read(void *);
int ext2fs_write(void *);
```
Just check for r/w, looks useful but we won't be using it until 64-bit is properly implemented. Judging by my guesses, if we implement mount correctly, reading and writing should not change for read only mode.
For the rest of the file, we don't have any other useful declarations; just `touch`, `ls`, `ln`, `rm`, etc implementations. We won't need to modify these too much yet, so let's move on.
I guess then, our second dive starts in `ext2fs_vfsops.c`. It's around 1142 lines, so let's read it in the next chapter.

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writeup/3.md Normal file
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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).