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.Dd April 17, 2005 .Dt FSS 4 .Os .Sh NAME .Nm fss , .Nm fssbs .Nd file system snapshot device .Sh SYNOPSIS .Cd "pseudo-device fss 4" .Sh DESCRIPTION The .Nm driver provides a read-only interface to the snapshot of a currently mounted file system. Reading from a .Nm device gives the view of the file system when the snapshot was taken. It can be configured via .Xr ioctl 2 . .Sh IOCTLS The .Xr ioctl 2 command codes below are defined in .Aq Pa sys/dev/fssvar.h .
p The (third) argument to .Xr ioctl 2 should be a pointer to the type indicated. l -tag -width 8n t Dv FSSIOCSET(struct fss_set) Configures a .Nm device. d -literal -offset indent struct fss_set { char *fss_mount; char *fss_bstore; blksize_t fss_csize; }; .Ed
p The struct element .Va fss_mount is the mount point of the file system. The struct element .Va fss_bstore is either a regular file or a raw disk device where data overwritten on the file system will be saved. The struct element .Va fss_csize is the preferred size of this data. t Dv FSSIOCGET(struct fss_get) Gets the status of a .Nm device. d -literal -offset indent struct fss_get { char fsg_mount[MNAMELEN]; struct timeval fsg_time; blksize_t fsg_csize; blkcnt_t fsg_mount_size; blkcnt_t fsg_bs_size; }; .Ed The struct element .Va fsg_mount is the mount point of the file system. The struct element .Va fsg_time is the time this snapshot was taken. The struct element .Va fsg_csize is the current size of data clusters. The struct element .Va fsg_mount_size is the number of clusters of the file system. The struct element .Va fsg_bs_size is the number of clusters written to the backing store. t Dv FSSIOCCLR Unconfigures a .Nm device. t Dv FSSIOFSET(int) Sets the flags of a .Nm device. Possible flags are: l -tag -width Dv t Dv FSS_UNCONFIG_ON_CLOSE Unconfigure the .Nm device on the last close. .El t Dv FSSIOFGET(int) Gets the flags of a .Nm device. .El .Sh KERNEL THREADS For each active snapshot device there is a kernel thread that handles the backing store. This thread is named .Va fssbsN where .Va N is the device minor number. .Sh FILES l -tag -width /dev/rfss? -compact t Pa /dev/rfss? t Pa /dev/fss? .El .Sh SEE ALSO .Xr fssconfig 8 , .Xr mount 8 , .Xr umount 8 .Sh HISTORY The .Nm device appeared in .Nx 2.0 . .Sh BUGS This driver is .Em experimental . Be sure you have a backup before you use it.