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.Dd April 28, 2021
.Dt GEOM_UZIP 4
.Os
.Sh NAME
.Nm geom_uzip
.Nd "GEOM based compressed disk images and partitions"
.Sh SYNOPSIS
To compile this driver into the kernel,
place the following line in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd "device xz"
.Cd "options zstd"
.Cd "options GEOM_UZIP"
.Ed
.Pp
Alternatively, to load the driver as a
module at boot time, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
geom_uzip_load="YES"
.Ed
.Sh DESCRIPTION
The
.Nm
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
.Nm
to detect compressed images which have been created with
.Xr mkuzip 8
and presented to the kernel as a logical disk device via
.Xr md 4 .
.Nm
creates a unique
.Pa md#.uzip
device for each image.
.Pp
.Nm
is not limited to supporting only
.Xr md 4
images.
The image can also reside on a block device.
.Pq For example, a disk, USB flash drive, DVD-ROM, etc .
The appropriate device node will appear with the
.Pa .uzip
suffix.
.Bd -literal -offset indent
# 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
.Ed
.Pp
The
.Nm
device is subsequently used by
.Fx
kernel to access the uncompressed data.
The
.Nm
driver does not allow write operations to the underlying disk image.
To check which
.Dq providers
match a given
.Nm
device:
.Bd -literal -offset indent
# 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
.Ed
.Pp
.Nm
allows mounting the root file system from a compressed disk partition by
setting the
.Dv vfs.root.mountfrom
tunable.
See
.Xr loader.conf 5
for details.
.Sh DIAGNOSTICS
Several flags are provided for tracing
.Nm
I/O operations and TOC parsing via the following sysctls.
.Bl -tag -width indent
.It Va kern.geom.uzip.debug
Log level.
Zero disables logging.
Higher values enable more verbose debug logging for
.Nm .
Supported levels are from 0 (no logging) to 4 (maximum amount of logging).
.It Va kern.geom.uzip.debug_block
Log operations involving compressed cluster number.
.El
.Sh SEE ALSO
.Xr GEOM 4 ,
.Xr md 4 ,
.Xr geom 8 ,
.Xr mkuzip 8
.Sh HISTORY
Zstd support was added in
.Fx 13.0 .
.Sh AUTHORS
.An -nosplit
The
.Nm
driver was written by
.An Max Khon Aq Mt fjoe@FreeBSD.org .
The block de-duplication code as well as some
.Nm
driver optimizations have been contributed by
.An Maxim Sobolev Aq Mt sobomax@FreeBSD.org .
The LZMA decompression support and CLOOP 3.0 support have been added by
.An Aleksandr Rybalko Aq Mt ray@FreeBSD.org .
.Pp
This manual page was written by
.An Ceri Davies Aq Mt ceri@FreeBSD.org .