1 .\" ----------------------------------------------------------------------------
2 .\" "THE BEER-WARE LICENSE" (Revision 42):
3 .\" <phk@FreeBSD.org> wrote this file. As long as you retain this notice you
4 .\" can do whatever you want with this stuff. If we meet some day, and you think
5 .\" this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
6 .\" ----------------------------------------------------------------------------
21 driver provides support for four kinds of memory backed virtual disks:
22 .Bl -tag -width preload
24 Backing store is allocated using
26 Only one malloc-bucket is used, which means that all
30 backing must share the malloc-per-bucket-quota.
31 The exact size of this quota varies, in particular with the amount
34 The exact value can be determined with
41 is used for backing store.
42 For backwards compatibility the type
45 If the kernel is created with option
47 the first preloaded image found will become the root file system.
49 A regular file is used as backing store.
50 This allows for mounting ISO images without the tedious
51 detour over actual physical media.
53 Backing store is allocated from buffer memory.
54 Pages get pushed out to the swap when the system is under memory
55 pressure, otherwise they stay in the operating memory.
58 backing is generally preferable over
63 For more information, please see
66 To create a kernel with a ramdisk or MD file system, your kernel config
67 needs the following options:
68 .Bd -literal -offset indent
69 options MD_ROOT # MD is a potential root device
70 options MD_ROOT_SIZE=8192 # 8MB ram disk
71 makeoptions MFS_IMAGE=/h/foo/ARM-MD
72 options ROOTDEVNAME=\\"ufs:md0\\"
77 will be loaded as the initial image each boot.
78 To create the image to use, please follow the steps to create a file-backed
82 Other tools will also create these images, such as NanoBSD.
93 driver first appeared in
95 as a cleaner replacement
96 for the MFS functionality previously used in
100 installation process.
104 driver did a hostile takeover of the
111 driver was written by
112 .An Poul-Henning Kamp
113 .Aq phk@FreeBSD.org .