loader: remove open_disk cache

[tsoome]

Summary

The recent rework on implementing support to read disk/partition size from
partition table and implementing more strict validation for reads in biosdisk.c
did reveal the problem with open_disk cache. To save the memory and based on
the fact that with ufs there was only one file system reader active at the time,
the open_disk data was cached and shared. The cache implementation is still
there and active, however, it really does not do any good in case of zfs,
because the disk devices are always open with pools.

Moreover, sharing the open disk info in case of multiple file systems on the
same disk can render the pool unreadable because the last partition size will
be stored in open_disk structure and since this structure is shared, the pool
IO will be limited to the last partition size.

The fix is relatively simple and straight forward - we just remove the cache
part, ensuring every opened disk device will get its own private instance of
open disk info and the structure data will not be disturbed.

Test Plan

To replicate the issue, it will help to construct a bit extreme layout
of the partitioning. What I did was following:

1. Allocate most of the disk from start for zpool.
2. Allocate relatively small partition after the pool.

Populate the /boot directory to the pool and verify the loader will start.

Now copy copy some data to the pool, to trigger the rootbp updates, the
dataset create is needed as well, so we could hope we get the rootbp
pointing far enough.

Confirm the boot loader will fail to read the pool, resulting with
MOS read errors.

The better proof can be achieved by printing out the disk/partition
size we get from disk_ioctl in biosdisk.c - so it can be verified that
indeed, in case of the shared open disk info, the wrong size is used,
namely, the size of the last partition of the particular disk.

Since the fix is removing the shared info, every open device will get
its private instance and the problem is gone.

[smh]

LGTM

[tsoome]

ptable_print needs to open the nested partition with disk_open,
as the state is not shared any more.

[allanjude]

Approved By: allanjude

[smh]

sys/boot/mips/beri/loader/beri_disk_sdcard.c

60 ↗

(On Diff #26288)

Is this alignment issue a reviews problem or actually in the code?

[tsoome]

whitespace cleanup

[tsoome]

sys/boot/mips/beri/loader/beri_disk_sdcard.c

60 ↗

(On Diff #26288)

After careful check - it was space issue, thanks.