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NetBSD 6.1.5 - man page for fss (netbsd section 4)

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

     fss -- file system snapshot device

     pseudo-device fss 4

     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).

     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 over-
	       written 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

     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.

	       Unconfigures a fss device.

	       Sets the flags of a fss device.	Possible flags are:

			     Unconfigure the fss device on the last close.

			     Unlink the backing file before the fss device is created.

	       Gets the flags of a fss device.

     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.


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

     The fss device appeared in NetBSD 2.0.

BSD					February 24, 2011				      BSD
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