geom_uzip4
Geom based compressed disk images and partitions
Usage
To compile this driver into the kernel, place the following line in your kernel configuration file:
device xz options zstd options GEOM_UZIP
Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5):
geom_uzip_load="YES"
Overview
The geom_uzip framework provides support for compressed read-only disk images. This allows significant storage savings at the expense of some CPU time on each read. Data written in the GEOM label area allows geom_uzip to detect compressed images which have been created with mkuzip(8) and presented to the kernel as a logical disk device via md(4). geom_uzip creates a unique md#.uzip device for each image.
geom_uzip is not limited to supporting only md(4) images. The image can also reside on a block device. (For example, a disk, USB flash drive, DVD-ROM, etc). The appropriate device node will appear with the .uzip suffix.
# gpart show da0
=> 0 7833600 da0 BSD (3.7G)
0 2097152 1 freebsd-ufs (1.0G)
2097152 5736448 - free - (2.7G)
# gpart add -t freebsd-ufs -s 1G da0
da0b added
# dd if=/tmp/20160217_dcomp_zcomp.uzip bs=256k of=/dev/da0b
3190+1 records in
3190+1 records out
836331008 bytes transferred in 111.021489 secs (7533055 bytes/sec)
# fsck -t ffs /dev/da0b.uzip
** /dev/da0b.uzip (NO WRITE)
** Last Mounted on /mnt
** Phase 1 - Check Blocks and Sizes
** Phase 2 - Check Pathnames
** Phase 3 - Check Connectivity
** Phase 4 - Check Reference Counts
** Phase 5 - Check Cyl groups
97455 files, 604242 used, 184741 free (2349 frags, 22799 blocks,
0.3% fragmentation)
# mount -o ro /dev/da0b.uzip /mnt
# df /dev/da0b.uzip
Filesystem 1K-blocks Used Avail Capacity Mounted on
/dev/da0b.uzip 3155932 2416968 738964 77% /mnt
The geom_uzip device is subsequently used by FreeBSD kernel to access the uncompressed data. The geom_uzip driver does not allow write operations to the underlying disk image. To check which “providers” match a given geom_uzip device:
# geom uzip list Geom name: md1.uzip Providers: 1. Name: md1.uzip Mediasize: 22003712 (21M) Sectorsize: 512 Consumers: 1. Name: md1 Mediasize: 9563648 (9.1M) Sectorsize: 512 Geom name: da0b.uzip Providers: 1. Name: da0b.uzip Mediasize: 3355443200 (3.1G) Sectorsize: 512 Consumers: 1. Name: da0b Mediasize: 1073741824 (1.0G) Sectorsize: 512
geom_uzip allows mounting the root file system from a compressed disk partition by setting the vfs.root.mountfrom tunable. See loader.conf(5) for details.
Diagnostics
Several flags are provided for tracing geom_uzip I/O operations and TOC parsing via the following sysctls.
- kern.geom.uzip.debug
-
Log level. Zero disables logging. Higher values enable more verbose debug logging for
geom_uzip. Supported levels are from 0 (no logging) to 4 (maximum amount of logging). - kern.geom.uzip.debug_block
-
Log operations involving compressed cluster number.
Releases
47 releases since FreeBSD 6.2-RELEASE; the text changed 33 times.