This corrects an issue introduced in b4cb3fe0e3, where a freshly
allocated `DOS_FS` structure would not be initialized properly before
use in `dos_open`.
In case of FAT32 file systems, this would leave `fs->dirents`
uninitialized and - depending on its content and due to checks in
`parsebs` - prevent mounting the file system successfully.
This particularily impacted the EFI loader, as it was sometimes not
able to read files from a FAT32-formatted EFI partition, including
LoaderEnv (`/efi/freebsd/loader.env`).
Accepted by: imp
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D36482
Fix layering violation and use devformat to get the string
representation of the device to see if we're mounted yet or not. Remove
added include to pickup disk.h.
Sponsored by: Netflix
Reviewed by: tsoome (prior version)
Differential Revision: https://reviews.freebsd.org/D35919
We want to keep our root file system open to preserve bcache segment
between file accesses, thus reducing physical disk IO.
Reviewed by: imp, allanjude, kevans (previous version)
Differential Revision: https://reviews.freebsd.org/D30848
MFC after: 1 month
