VFS_BUSY(9) Kernel Developer's Manual VFS_BUSY(9)

vfs_busy, vfs_isbusy, vfs_unbusyVFS locking API

#include <sys/mount.h>

vfs_busy(struct mount *mp, int flags);

vfs_isbusy(struct mount *mp);

vfs_unbusy(struct mount *mp);

The vfs_busy API is used to lock mount points to ensure consistent access. A read lock can be shared between multiple processes, while a write lock is exclusive. Normally a write lock is only acquired when unmounting.

The () function locks the mount point pointed to by mp, where flags describes the type of lock to acquire and whether or not to wait for a conflicting lock to be released. The following flags are available:

Acquire a read lock.
Acquire a write lock.
Return immediately; do not wait for the conflicting lock to be released.
Wait for the conflicting lock to be released.
Prevent witness(4) from logging when this thread already has a mount point locked.

If a conflicting lock was encountered, () returns an error.

The () function checks whether the given mount point is locked.

() unlocks the given mount point.

The vfs_busy API is implemented in the file sys/kern/vfs_subr.c.

witness(4), rwlock(9), vfs(9)

June 4, 2018 OpenBSD 7.5