When an FS crashes, VFS will clean up resources tied to that FS:
- Pending requests to the FS are canceled (i.e., fail with EIO)
- Threads waiting for a reply are stopped (i.e., fail with EIO)
- Open files are marked invalid. Future operations on a file descriptor
will cause EBADF errors.
- vmnt entry is cleared, so in-flight system calls that got past the
file descriptor check but not yet talking to the crashed FS, will
fail with EIO.
- The reference counter of the mount point is decreased, effectively
removing the crashed FS from the file system tree. Descendants of
this part of the tree are unreachable by means of a path, but can
still be unmounted by feeding the block special file to unmount(2).
This patch also gets rid of the "not a known driver endpoint" messages
during shutdown.
Using sendrec directly only results in problems. While it is not
clear whether using fs_sendrec is the best option, it is at least
an improvement.
Also remove some legacy cruft.
PUFFS file systems need to make back calls for every operation we
send to them. Consequently, they cannot handle block reads and writes
themselves. Instead, the root file system has to do it (for now).
When the mount operation causes an FS to make a back call, AVFS now
concludes that every block read and write for that FS has to go
through the root file system.
