1.\" $NetBSD: fss.4,v 1.10 2008/04/30 13:10:54 martin Exp $ */ 2.\" 3.\" 4.\" Copyright (c) 2003 The NetBSD Foundation, Inc. 5.\" All rights reserved. 6.\" 7.\" This code is derived from software contributed to The NetBSD Foundation 8.\" by Juergen Hannken-Illjes. 9.\" 10.\" Redistribution and use in source and binary forms, with or without 11.\" modification, are permitted provided that the following conditions 12.\" are met: 13.\" 1. Redistributions of source code must retain the above copyright 14.\" notice, this list of conditions and the following disclaimer. 15.\" 2. Redistributions in binary form must reproduce the above copyright 16.\" notice, this list of conditions and the following disclaimer in the 17.\" documentation and/or other materials provided with the distribution. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 20.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 21.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 22.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 23.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 24.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 25.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 26.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 27.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 28.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 29.\" POSSIBILITY OF SUCH DAMAGE. 30.\" 31.Dd April 17, 2005 32.Dt FSS 4 33.Os 34.Sh NAME 35.Nm fss , 36.Nm fssbs 37.Nd file system snapshot device 38.Sh SYNOPSIS 39.Cd "pseudo-device fss 4" 40.Sh DESCRIPTION 41The 42.Nm 43driver provides a read-only interface to the snapshot of a currently 44mounted file system. 45Reading from a 46.Nm 47device gives the view of the file system when the snapshot was taken. 48It can be configured via 49.Xr ioctl 2 . 50.Sh IOCTLS 51The 52.Xr ioctl 2 53command codes below are defined in 54.Aq Pa sys/dev/fssvar.h . 55.Pp 56The (third) argument to 57.Xr ioctl 2 58should be a pointer to the type indicated. 59.Bl -tag -width 8n 60.It Dv FSSIOCSET(struct fss_set) 61Configures a 62.Nm 63device. 64.Bd -literal -offset indent 65struct fss_set { 66 char *fss_mount; 67 char *fss_bstore; 68 blksize_t fss_csize; 69}; 70.Ed 71.Pp 72The struct element 73.Va fss_mount 74is the mount point of the file system. 75The struct element 76.Va fss_bstore 77is either a regular file or a raw disk device where data overwritten on 78the file system will be saved. 79The struct element 80.Va fss_csize 81is the preferred size of this data. 82.It Dv FSSIOCGET(struct fss_get) 83Gets the status of a 84.Nm 85device. 86.Bd -literal -offset indent 87struct fss_get { 88 char fsg_mount[MNAMELEN]; 89 struct timeval fsg_time; 90 blksize_t fsg_csize; 91 blkcnt_t fsg_mount_size; 92 blkcnt_t fsg_bs_size; 93}; 94.Ed 95The struct element 96.Va fsg_mount 97is the mount point of the file system. 98The struct element 99.Va fsg_time 100is the time this snapshot was taken. 101The struct element 102.Va fsg_csize 103is the current size of data clusters. 104The struct element 105.Va fsg_mount_size 106is the number of clusters of the file system. 107The struct element 108.Va fsg_bs_size 109is the number of clusters written to the backing store. 110.It Dv FSSIOCCLR 111Unconfigures a 112.Nm 113device. 114.It Dv FSSIOFSET(int) 115Sets the flags of a 116.Nm 117device. 118Possible flags are: 119.Bl -tag -width Dv 120.It Dv FSS_UNCONFIG_ON_CLOSE 121Unconfigure the 122.Nm 123device on the last close. 124.El 125.It Dv FSSIOFGET(int) 126Gets the flags of a 127.Nm 128device. 129.El 130.Sh KERNEL THREADS 131For each active snapshot device there is a kernel thread 132that handles the backing store. 133This thread is named 134.Va fssbsN 135where 136.Va N 137is the device minor number. 138.Sh FILES 139.Bl -tag -width /dev/rfss? -compact 140.It Pa /dev/rfss? 141.It Pa /dev/fss? 142.El 143.Sh SEE ALSO 144.Xr fssconfig 8 , 145.Xr mount 8 , 146.Xr umount 8 147.Sh HISTORY 148The 149.Nm 150device appeared in 151.Nx 2.0 . 152.Sh BUGS 153This driver is 154.Em experimental . 155Be sure you have a backup before you use it. 156