379 lines
12 KiB
Groff
379 lines
12 KiB
Groff
.\" $NetBSD: vfsops.9,v 1.27 2006/10/04 11:35:47 pooka Exp $
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.\"
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.\" Copyright (c) 2001 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Gregory McGarry.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the NetBSD
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.\" Foundation, Inc. and its contributors.
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.\" 4. Neither the name of The NetBSD Foundation nor the names of its
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.\" contributors may be used to endorse or promote products derived
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.\" from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd October 4, 2006
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.Dt VFSOPS 9
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.Os
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.Sh NAME
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.Nm vfsops ,
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.Nm VFS_MOUNT ,
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.Nm VFS_START ,
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.Nm VFS_UNMOUNT ,
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.Nm VFS_ROOT ,
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.Nm VFS_QUOTACTL ,
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.Nm VFS_STATVFS ,
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.Nm VFS_SYNC ,
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.Nm VFS_VGET ,
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.Nm VFS_FHTOVP ,
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.Nm VFS_VPTOFH ,
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.Nm VFS_SNAPSHOT
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.Nd kernel file system interface
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/mount.h
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.In sys/vnode.h
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.Ft int
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.Fn VFS_MOUNT "struct mount *mp" "const char *path" "void *data" \
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"struct nameidata *ndp" "struct lwp *l"
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.Ft int
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.Fn VFS_START "struct mount *mp" "int flags" "struct lwp *l"
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.Ft int
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.Fn VFS_UNMOUNT "struct mount *mp" "int mntflags" "struct lwp *l"
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.Ft int
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.Fn VFS_ROOT "struct mount *mp" "struct vnode **vpp"
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.Ft int
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.Fn VFS_QUOTACTL "struct mount *mp" "int cmds" "uid_t uid" \
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"caddr_t arg" "struct lwp *l"
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.Ft int
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.Fn VFS_STATVFS "struct mount *mp" "struct statvfs *sbp" "struct lwp *l"
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.Ft int
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.Fn VFS_SYNC "struct mount *mp" "int waitfor" "kauth_cred_t cred" \
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"struct lwp *l"
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.Ft int
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.Fn VFS_VGET "struct mount *mp" "ino_t ino" "struct vnode **vpp"
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.Ft int
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.Fn VFS_FHTOVP "struct mount *mp" "struct fid *fhp" "struct vnode **vpp"
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.Ft int
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.Fn VFS_VPTOFH "struct vnode *vp" "struct fid *fhp"
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.Ft int
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.Ft int
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.Fn VFS_SNAPSHOT "struct mount *mp" "struct vnode *vp" "struct timespec *ts"
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.Sh DESCRIPTION
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In a similar fashion to the
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.Xr vnode 9
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interface, all operations that are done on a file system are conducted
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through a single interface that allows the system to carry out
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operations on a file system without knowing its construction or type.
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.Pp
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All supported file systems in the kernel have an entry in the
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.Va vfs_list_initial
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table.
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This table is generated by
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.Xr config 1
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and is a
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.Dv NULL Ns No -terminated
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list of
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.Em vfsops
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structures.
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The vfsops structure describes the operations that can be done to a
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specific file system type.
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The following table lists the elements of the vfsops vector, the
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corresponding invocation macro, and a description of the element.
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.Pp
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.nf
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.ta \w'int (*vfs_mountroot)()'u+2n +\w'VFS_QUOTACTL'u+2n +\w'Get the file system root vnode'u
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\fIVector element\fP \fIMacro\fP \fIDescription\fP
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.ta \w'int (*vfs_mountroot)()'u+2n +\w'VFS_QUOTACTL'u+2n +\w'Get the file system root vnode'u+6nC
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.sp 5p
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int (*vfs_mount)() VFS_MOUNT Mount a file system
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int (*vfs_start)() VFS_START Make operational
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int (*vfs_unmount)() VFS_UMOUNT Unmount a file system
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int (*vfs_root)() VFS_ROOT Get the file system root vnode
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int (*vfs_quotactl)() VFS_QUOTACTL Query/modify space quotas
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int (*vfs_statvfs)() VFS_STATVFS Get file system statistics
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int (*vfs_sync)() VFS_SYNC Flush file system buffers
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int (*vfs_vget)() VFS_VGET Get vnode from file id
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int (*vfs_fhtovp)() VFS_FHTOVP NFS file handle to vnode lookup
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int (*vfs_vptofh)() VFS_VPTOFH Vnode to NFS file handle lookup
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void (*vfs_init)() - Initialise file system
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void (*vfs_reinit)() - Reinitialise file system
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void (*vfs_done)() - Cleanup unmounted file system
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int (*vfs_mountroot)() - Mount the root file system
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int (*vfs_snapshot)() VFS_SNAPSHOT Take a snapshot
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.fi
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.Pp
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Some additional non-function members of the vfsops structure are the
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file system name
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.Ns Em vfs_name
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and a reference count
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.Ns Em vfs_refcount .
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It is not mandatory for a file system type to support a particular
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operation, but it must assign each member function pointer to a
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suitable function to do the minimum required of it.
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In most cases, such functions either do nothing or return an error
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value to the effect that it is not supported.
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.Em vfs_reinit ,
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.Em vfs_mountroot ,
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.Em vfs_fhtovp ,
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and
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.Em vfs_vptofh
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may
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be
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.Dv NULL .
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.Pp
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At system boot, each file system with an entry in
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.Va vfs_list_initial
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is established and initialised.
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Each initialised file system is recorded by the kernel in the list
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.Va vfs_list
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and the file system specific initialisation function
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.Em vfs_init
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in its vfsops vector is invoked.
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When the file system is no longer needed
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.Em vfs_done
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is invoked to run file system specific cleanups and the file system is
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removed from the kernel list.
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.Pp
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At system boot, the root filesystem is mounted by invoking the file
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system type specific
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.Em vfs_mountroot
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function in the vfsops vector.
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All filesystems that can be mounted as a root file system must define
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this function.
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It is responsible for initialising to list of mount structures for
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all future mounted file systems.
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.Pp
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Kernel state which affects a specific file system type can be
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queried and modified using the
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.Xr sysctl 8
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interface.
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.Sh FUNCTIONS
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.Bl -tag -width compact
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.It Fn VFS_MOUNT "mp" "path" "data" "ndp" "l"
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Mount a file system specified by the mount structure
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.Fa mp
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on the mount point described by
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.Fa path .
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The argument
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.Fa data
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contains file system type specific data and is read into the kernel
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using
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.Xr copyin 9 .
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The argument
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.Fa ndp
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contains the result of a
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.Xr namei 9
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call on the pathname of the mount point and
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.Fa p
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is the calling process.
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.Fn VFS_MOUNT
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initialises the mount structure for the mounted file system.
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This structure records mount-specific information for the file system and
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records the list of vnodes associated with the file system.
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This function is invoked both to mount new file systems and to change the
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attributes of an existing file system.
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If the MNT_UPDATE flag is set in
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.Em mp-\*[Gt]mnt_flag
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then the filesystem should update its internal state from the value of
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.Em mp-\*[Gt]mnt_flag .
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This can be used, for instance, to convert a read-only filesystem to
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read-write.
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If the MNT_UPDATE flag is not specified, then this is a newly
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mounted filesystem.
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.It Fn VFS_START "mp" "flags" "l"
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Make the file system specified by the mount structure
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.Fa mp
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operational.
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The argument
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.Fa p
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is the calling process.
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The argument
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.Fa flags
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is a set of flags for controlling the operation of
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.Fn VFS_START .
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This function is invoked after
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.Fn VFS_MOUNT
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and before the first access to the file system.
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.It Fn VFS_UNMOUNT "mp" "mntflags" "l"
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Unmount a file system specified by the mount structure
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.Fa mp .
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The argument
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.Fa p
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is the calling process.
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.Fn VFS_UNMOUNT
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performs any file system type specific operations required before the
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file system is unmounted, such are flushing buffers.
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If MNT_FORCE is specified in the flags
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.Fa mntflags
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then open files are forcibly closed.
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The function also deallocates space associated with data structure
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that were allocated for the file system when it was mounted.
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.It Fn VFS_ROOT "mp" "vpp"
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Get the root vnode of the file system specified by the mount
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structure
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.Fa mp .
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The vnode is returned in the address given by
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.Fa vpp .
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This function is used by the pathname translation algorithms when a
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vnode that has been covered by a mounted file system is encountered.
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While resolving the pathname, the pathname translation algorithm will
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have to go through the directory tree in the file system associated
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with that mount point and therefore requires the root vnode of the
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file system.
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.It Fn VFS_QUOTACTL "mp" "cmds" "uid" "arg" "l"
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Query/modify user space quotas for the file system specified by the
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mount structure
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.Fa mp .
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The argument specifies the control command to perform.
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The userid is specified in
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.Fa id ,
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the calling process is
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.Fa p
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and
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.Fa arg
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allows command-specific data to be returned to the system call
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interface.
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.Fn VFS_QUOTACTL
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is the file system type specific implementation of the
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.Xr quotactl 2
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system call.
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.It Fn VFS_STATVFS "mp" "sbp" "l"
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Get file system statistics for the file system specified by the mount
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structure
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.Fa mp .
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The argument
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.Fa p
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is the calling process.
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A statvfs structure filled with the statistics is returned in
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.Fa sbp .
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.Fn VFS_STATVFS
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is the file system type specific implementation of the
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.Xr statvfs 2
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and
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.Xr fstatvfs 2
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system calls.
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.It Fn VFS_SYNC "mp" "waitfor" "cred" "l"
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Flush file system I/O buffers for the file system specified by the mount
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structure
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.Fa mp .
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The
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.Fa waitfor
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argument indicates whether a partial flush or complete flush should be
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performed.
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The arguments
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.Fa l
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and
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.Fa cred
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specific the calling lwp and its credentials, respectively.
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.Fn VFS_SYNC
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does not provide any return value since the operation can never fail.
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.It Fn VFS_VGET "mp" "ino" "vpp"
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Get vnode for a file system type specific file id
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.Fa ino
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for the file system specified by the mount structure
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.Fa mp .
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The vnode is returned in the address specified
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.Fa vpp .
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The function is optional for file systems which have a unique id
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number for every file in the file system.
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It is used internally by the UFS file system and also by the NFSv3
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server to implement the READDIRPLUS nfs call.
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If the file system does not support this function, it should return
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.Er EOPNOTSUPP .
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.It Fn VFS_FHTOVP "mp" "fhp" "vpp"
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Get the vnode for the NFS file specified by the file handle
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.Fa fhp
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in the file system specified by the mount structure
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.Fa mp .
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The locked vnode is returned in
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.Fa vpp .
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.Pp
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A call to
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.Fn VFS_FHTOVP
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should generally be followed by a call to
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.Fn nfs_check_export
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to check if the file is accessable to the client.
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.Pp
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If this function's pointer is set to
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.Dv NULL ,
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the underlying file system will not be NFS exportable.
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If it is defined, though,
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.Fn VFS_VPTOFH
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must be defined too.
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.It Fn VFS_VPTOFH "vp" "fhp"
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Get a unique NFS file handle for the file specified by the vnode
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.Fa vp .
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The file handle is returned in
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.Fa fhp .
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The contents of the file handle are defined by the file system and are
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not examined by any other subsystems.
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It should contain enough information to uniquely identify a file within
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the file system as well as noticing when a file has been removed and
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the file system resources have been recycled for a new file.
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.Pp
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If this function's pointer is set to
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.Dv NULL ,
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the underlying file system will not be NFS exportable.
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If it is defined, though,
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.Fn VFS_FHTOVP
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must be defined too.
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.It Fn VFS_SNAPSHOT "mp" "vp" "ts"
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Take a snapshot of the file system specified by the mount structure
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.Fa mp
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and make it accessible through the locked vnode
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.Fa vp .
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If
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.Fa ts
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is not
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.Dv NULL
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it will receive the time this snapshot was taken.
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If the file system does not support this function, it should return
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.Er EOPNOTSUPP .
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.El
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.Sh CODE REFERENCES
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This section describes places within the
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.Nx
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source tree where actual code implementing or using the vfs
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operations can be found.
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All pathnames are relative to
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.Pa /usr/src .
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.Pp
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The vfs operations are implemented within the files
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.Pa sys/kern/vfs_subr.c
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and
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.Pa sys/kern/vfs_init.c .
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.Sh SEE ALSO
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.Xr intro 9 ,
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.Xr namei 9 ,
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.Xr vfs 9 ,
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.Xr vfssubr 9 ,
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.Xr vnode 9 ,
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.Xr vnodeops 9
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.Sh HISTORY
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The vfs operations vector, its functions and the corresponding macros
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appeared in
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.Bx 4.3 .
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