Copyright (c) 2006 Nikolay Sturm <sturm@openbsd.org>
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.Dd $Mdocdate: May 31 2007 $ .Dt VFS_BUSY 9 .Os .Sh NAME .Nm vfs_busy , .Nm vfs_isbusy , .Nm vfs_unbusy .Nd VFS locking API .Sh SYNOPSIS n sys/mount.h
p .Ft int .Fn vfs_busy "struct mount *mp" "int flags" .Ft int .Fn vfs_isbusy "struct mount *mp" .Ft void .Fn vfs_unbusy "struct mount *mp" .Sh DESCRIPTION The .Nm 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.
p The .Fn vfs_busy function locks the mount point pointed to by .Fa mp , where .Fa 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:
p l -tag -width "VB_NOWAITXX" -offset indent -compact t VB_READ Acquire a read lock. t VB_WRITE Acquire a write lock. t VB_NOWAIT Return immediately; do not wait for the conflicting lock to be released. t VB_WAIT Wait for the conflicting lock to be released. t VB_DUPOK Prevent .Xr witness 4 from logging when this thread already has a mount point locked. .El
p If a conflicting lock was encountered, .Fn vfs_busy returns an error.
p The .Fn vfs_isbusy function checks whether the given mount point is locked.
p .Fn vfs_unbusy unlocks the given mount point.
p The .Nm vfs_busy API is implemented in the file
a sys/kern/vfs_subr.c . .Sh SEE ALSO .Xr witness 4 , .Xr rwlock 9 , .Xr vfs 9