TARFS(4)

NAME
tarfs - tarball filesystem

SYNOPSIS
To compile this driver into the kernel, place the following line in your kernel configuration file:

options TARFS

Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5):

    tarfs_load="YES"

DESCRIPTION
The tarfs driver implements a read-only filesystem backed by a tar(5) file. Currently, only POSIX archives, optionally compressed with zstd(1), are supported.

The preferred I/O size for tarfs filesystems can be adjusted using the vfs.tarfs.ioshift sysctl setting and tunable. Setting it to 0 will reset it to its default value. Note that changes to this setting only apply to filesystems mounted after the change.

When the backing tar file is compressed with zstd(1), I/O performance can be improved by ensuring that compressed data is broken up into multiple frames. This helps minimize unnecessary decompression work. When using bsdtar(1) to create the tar file, this can be achieved using the zstd:max-frame-size and zstd:frame-per-file options. Sensible frame sizes are powers of 2 between the system's base page size (see arch(7)) and the value of the kern.maxphys sysctl. Smaller frames will generally yield a worse compression ratio and require extra kernel memory to maintain an index, and larger frames will on average require more CPU time to access data when performing random I/O.

DIAGNOSTICS
If enabled by the TARFS_DEBUG kernel option, the vfs.tarfs.debug sysctl setting can be used to control debugging output from the tarfs driver. Debugging output for individual sections of the driver can be enabled by adding together the relevant values from the table below.
0x01 | Memory allocations
0x02 | Checksum calculations
0x04 | Filesystem operations (vfsops)
0x08 | Path lookups
0x10 | File operations (vnops)
0x20 | General I/O
0x40 | Decompression
0x80 | Decompression index
0x100 | Sparse file mapping
0x200 | Bounce buffer usage

SEE ALSO
tar(1), zstd(1), fstab(5), tar(5), mount(8), sysctl(8)

HISTORY
-nosplit The tarfs driver was developed by Stephen J. Kiernan <stevek@FreeBSD.org> and Dag-Erling Smørgrav <des@FreeBSD.org> for Juniper Networks and Klara Systems. This manual page was written by Dag-Erling Smørgrav <des@FreeBSD.org> for Juniper Networks and Klara Systems.