| FSS(4) | Device Drivers Manual | FSS(4) | 
fss —
pseudo-device fss 4
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).
<sys/dev/fssvar.h>.
The (third) argument to ioctl(2) should be a pointer to the type indicated.
FSSIOCSET(struct
    fss_set)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)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;
};
    
    FSSIOCCLRfss device.FSSIOFSET(int)fss device. Possible flags
      are:
    FSS_UNCONFIG_ON_CLOSEfss device on the last
        close.FSS_UNLINK_ON_CREATEfss device
          is created.FSSIOFGET(int)fss device.fss device appeared in NetBSD
  2.0.
| February 24, 2011 | NetBSD 9.4 |