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download PDF document: tarfs.5.pdf

TARFS(5) FreeBSD File Formats Manual TARFS(5)
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 The tarfs driver was developed by Stephen J. Kiernan <stevek@FreeBSD.org>