225 lines
6.1 KiB
Groff
225 lines
6.1 KiB
Groff
.\" $NetBSD: fstrans.9,v 1.14 2009/06/24 22:39:40 zafer Exp $
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.\"
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.\" Copyright (c) 2007 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 Juergen Hannken-Illjes.
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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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.\"
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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 December 2, 2007
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.Dt FSTRANS 9
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.Os
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.Sh NAME
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.Nm fstrans ,
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.Nm fstrans_setstate ,
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.Nm fstrans_getstate ,
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.Nm fstrans_start ,
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.Nm fstrans_start_nowait ,
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.Nm fstrans_done ,
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.Nm fstrans_is_owner ,
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.Nm fscow_establish ,
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.Nm fscow_disestablish ,
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.Nm fscow_run
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.Nd file system suspension helper subsystem
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.Sh SYNOPSIS
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.In sys/mount.h
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.In sys/fstrans.h
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.Ft int
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.Fn fstrans_setstate "struct mount *mp" "enum fstrans_state new_state"
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.Ft "enum fstrans_state"
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.Fn fstrans_getstate "struct mount *mp"
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.Ft void
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.Fn fstrans_start "struct mount *mp" "enum fstrans_lock_type lock_type"
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.Ft int
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.Fn fstrans_start_nowait "struct mount *mp" "enum fstrans_lock_type lock_type"
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.Ft void
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.Fn fstrans_done "struct mount *mp"
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.Ft int
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.Fn fstrans_is_owner "struct mount *mp"
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.Ft int
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.Fn fscow_establish "struct mount *mp" \
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"int (*func)(void *, struct buf *, bool)" "void *cookie"
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.Ft int
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.Fn fscow_disestablish "struct mount *mp" \
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"int (*func)(void *, struct buf *, bool)" "void *cookie"
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.Ft int
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.Fn fscow_run "struct buf *bp" "bool data_valid"
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.Sh DESCRIPTION
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The
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.Nm
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subsystem is a set of operations to assist file system suspension.
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These operations must not be used outside of file systems.
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.Pp
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File systems supporting this subsystem must set the flag
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.Dv IMNT_HAS_TRANS
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in
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.Dv "mnt_iflag" .
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.Pp
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File systems are always in one of these states:
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.Bl -tag -offset indent -width FSTRANS_SUSPENDING -compact
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.It Dv FSTRANS_NORMAL
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normal operations.
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.It Dv FSTRANS_SUSPENDING
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preparing a suspension.
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.It Dv FSTRANS_SUSPENDED
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suspended.
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.El
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This state is represented by
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.Vt "enum fstrans_state" .
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.Bl -tag -width compact
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.It Fn fstrans_getstate "mp"
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returns the current state of the file system
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.Fa mp .
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.Pp
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.It Fn fstrans_setstate "mp" "new_state"
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changes the state of the file system
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.Fa mp
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to
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.Fa new_state .
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.El
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.Pp
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All file system operations use a
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.Em "fstrans lock" .
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This lock is recursive.
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A thread already owning a lock will always get another lock.
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The lock has two variants:
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.Bl -tag -offset indent -width FSTRANS_SHARED -compact
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.It Dv FSTRANS_SHARED
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this lock will be granted if the file system is in state
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.Dv FSTRANS_NORMAL .
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.It Dv FSTRANS_LAZY
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this lock will be granted if the file system is in state
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.Dv FSTRANS_NORMAL
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or
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.Dv FSTRANS_SUSPENDING .
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It needs special care because operations using this variant will not block
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while the file system prepares suspension.
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.El
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The lock variant is represented by
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.Vt "enum fstrans_lock_type" .
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.Bl -tag -width compact
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.It Fn fstrans_start "mp" "lock_type"
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sets a lock of type
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.Fa lock_type
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on the file system
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.Fa mp .
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.It Fn fstrans_start_nowait "mp" "lock_type"
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will not wait for a state change of the file system when attempting to
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acquire the lock.
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The thread may still sleep while attempting to acquire the lock.
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.It Fn fstrans_done "mp"
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releases a lock on the file system
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.Fa mp .
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.It Fn fstrans_is_owner "mp"
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returns
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.Dv true
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if this thread is currently suspending the file system
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.Fa mp .
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.It Fn fscow_establish "mp" "func" "cookie"
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Establish a copy-on-write callback for the file system
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.Fa mp .
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.Fa func
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will be called for every buffer written through this file system.
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.It Fn fscow_disestablish "mp" "func" "cookie"
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Disestablish a copy-on-write callback registered with
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.Fn fscow_establish .
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.It Fn fscow_run "bp" "data_valid"
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Run all copy-on-write callbacks established for the file system this buffer
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belongs to.
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If
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.Fa data_valid
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is
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.Dv true
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the buffer data has not yet been modified.
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.El
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.Sh RETURN VALUES
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The functions
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.Fn fstrans_setstate
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and
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.Fn fstrans_start_nowait
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return zero on success and an error value on failure.
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.Sh EXAMPLES
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The following is an example of a file system suspend operation.
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.Bd -literal
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int
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xxx_suspendctl(struct mount *mp, int cmd)
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{
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int error;
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switch (cmd) {
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case SUSPEND_SUSPEND:
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error = fstrans_setstate(mp, FSTRANS_SUSPENDING);
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if (error != 0)
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return error;
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/* Sync file system state to disk. */
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return fstrans_setstate(mp, FSTRANS_SUSPENDED);
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case SUSPEND_RESUME:
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return fstrans_setstate(mp, FSTRANS_NORMAL);
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default:
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return EINVAL;
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}
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}
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.Ed
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.Pp
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This is an example of a file system operation.
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.Bd -literal
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int
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xxx_create(void *v)
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{
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struct vop_create_args *ap = v;
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struct mount *mp = ap-\*[Gt]a_dvp-\*[Gt]v_mount;
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int error;
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if ((error = fstrans_start(mp, FSTRANS_SHARED)) != 0)
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return error;
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/* Actually create the node. */
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fstrans_done(mp);
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return 0;
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}
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.Ed
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.Sh SEE ALSO
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.Xr vfs_resume 9 ,
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.Xr vfs_suspend 9
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.Sh CODE REFERENCES
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The actual code implementing this subsystem can be found in the file
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.Pa sys/kern/vfs_trans.c .
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.Sh HISTORY
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The
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.Nm
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subsystem appeared in
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.Nx 5.0 .
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.Sh AUTHORS
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The
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.Nm
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subsystem was written by
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.An J\(:urgen Hannken-Illjes
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.Aq hannken@NetBSD.org .
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