FSS(4)							   BSD Kernel Interfaces Manual 						    FSS(4)

NAME

     fss -- file system snapshot device

SYNOPSIS

     pseudo-device fss 4

DESCRIPTION

     The fss driver provides a read-only interface to the snapshot of a currently mounted file system.	Reading from a fss device gives the view
     of the file system when the snapshot was taken.  It can be configured via ioctl(2).

IOCTLS

     The ioctl(2) command codes below are defined in <sys/dev/fssvar.h>.

     The (third) argument to ioctl(2) should be a pointer to the type indicated.

     FSSIOCSET(struct fss_set)
	       Configures a fss device.

		     struct fss_set {
			     char *fss_mount;
			     char *fss_bstore;
			     blksize_t fss_csize;
			     int fss_flags;
		     };

	       The struct element fss_mount is the mount point of the file system.  The struct element 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 fss_csize is the preferred size of
	       this data.  The struct element fss_flags is the initial set of flags.

     FSSIOCGET(struct fss_get)
	       Gets the status of a fss device.

		     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;
		     };
	       The struct element fsg_mount is the mount point of the file system.  The struct element fsg_time is the time this snapshot was
	       taken.  The struct element fsg_csize is the current size of data clusters.  The struct element fsg_mount_size is the number of
	       clusters of the file system.  The struct element fsg_bs_size is the number of clusters written to the backing store.

     FSSIOCCLR
	       Unconfigures a fss device.

     FSSIOFSET(int)
	       Sets the flags of a fss device.	Possible flags are:

	       FSS_UNCONFIG_ON_CLOSE
			     Unconfigure the fss device on the last close.

	       FSS_UNLINK_ON_CREATE
			     Unlink the backing file before the fss device is created.

     FSSIOFGET(int)
	       Gets the flags of a fss device.

KERNEL THREADS

     For each active snapshot device there is a kernel thread that handles the backing store.  This thread is named fssN where N is the device
     minor number.

FILES

     /dev/rfss?
     /dev/fss?

SEE ALSO

     fssconfig(8), mount(8), umount(8)

HISTORY

     The fss device appeared in NetBSD 2.0.

BSD
								 February 24, 2011							       BSD