42d0626726
Simplify the mount locking. Remove all the crud to deal with recursion on the mount lock, and crud to deal with unmount as another weirdo lock. Hopefully this will once and for all fix the deadlocks with this. With this commit there are two locks on each mount: - krwlock_t mnt_unmounting. This is used to prevent unmount across critical sections like getnewvnode(). It's only ever read locked with rw_tryenter(), and is only ever write locked in dounmount(). A write hold can't be taken on this lock if the current LWP could hold a vnode lock. - kmutex_t mnt_updating. This is taken by threads updating the mount, for example when going r/o -> r/w, and is only present to serialize updates. In order to take this lock, a read hold must first be taken on mnt_unmounting, and the two need to be held across the operation. One effect of this change: previously if an unmount failed, we would make a half hearted attempt to back out of it gracefully, but that was unlikely to work in a lot of cases. Now while an unmount that will be aborted is in progress, new file operations within the mount will fail instead of being delayed. That is unlikely to be a problem though, because if the admin requests unmount of a file system then s(he) has made a decision to deny access to the resource.
$NetBSD: README.dirs,v 1.3 2007/08/16 19:56:22 pooka Exp $
Runnable Userspace Meta Programs
Quick rundown of the current directory structure:
/librump - kernel runtime emulation
/rumpkern - portion compiled with -D_KERNEL, uses kernel headers
/rumpuser - userspace namespace support for previous, *NO* -D_KERNEL
provides e.g. malloc() and some syscalls
/include
/machine - headers meant to be used for rump compilation when the MD
ones cause too much trouble, e.g. curlwp which is different
from arch to arch
/fs - file system rumps
/lib - libraries used by fs rumps
/lib$fs - kernel file system code compiled out of /sys with -D_KERNEL
/libp2k - puffs-to-vfs adaption layer, userspace namespace
/libukfs - user kernel file system, a library to access file system
images (or devices) directly in userspace without going
through a system call and puffs
/bin - rumps themselves. fsconsole uses ukfs directly. the rest are
file system specific rumps and use puffs