FSS(4)                  NetBSD 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 cur- rently 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 indi- cated. 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. NetBSD 8.1 February 24, 2011 NetBSD 8.1

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