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.