We found that when writing a large file through buffer write, if the
disk is inaccessible, exFAT does not return an error normally, which
leads to the writing process not stopping properly.

To easily reproduce this issue, you can follow the steps below:

1. format a device to exFAT and then mount (with a full disk erase)
2. dd if=/dev/zero of=/exfat_mount/test.img bs=1M count=8192
3. eject the device

You may find that the dd process does not stop immediately and may
continue for a long time.

The root cause of this issue is that during buffer write process,
exFAT does not need to access the disk to look up directory entries
or the FAT table (whereas FAT would do) every time data is written.
Instead, exFAT simply marks the buffer as dirty and returns,
delegating the writeback operation to the writeback process.

If the disk cannot be accessed at this time, the error will only be
returned to the writeback process, and the original process will not
receive the error, so it cannot be returned to the user side.

When the disk cannot be accessed normally, an error should be returned
to stop the writing process.

Implement sops->shutdown and ioctl to shut down the file system
when underlying block device is marked dead.
Signed-off-by: Dongliang Cui <dongliang.cui@unisoc.com>
Signed-off-by: Zhiguo Niu <zhiguo.niu@unisoc.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>