NAME
vfs_busy,
vfs_isbusy, vfs_unbusy
— VFS locking API
SYNOPSIS
#include
<sys/mount.h>
int
vfs_busy(struct
mount *mp, int
flags);
int
vfs_isbusy(struct
mount *mp);
void
vfs_unbusy(struct
mount *mp);
DESCRIPTION
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
vfs_busy()
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:
- VB_READ
- Acquire a read lock.
- VB_WRITE
- Acquire a write lock.
- VB_NOWAIT
- Return immediately; do not wait for the conflicting lock to be released.
- VB_WAIT
- Wait for the conflicting lock to be released.
- VB_DUPOK
- Prevent witness(4) from logging when this thread already has a mount point locked.
If a conflicting lock was encountered,
vfs_busy()
returns an error.
The
vfs_isbusy()
function checks whether the given mount point is locked.
vfs_unbusy()
unlocks the given mount point.
The vfs_busy API is implemented in the
file sys/kern/vfs_subr.c.