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Ubifs产生背景：
无排序区块图像文件系统(Unsorted Block Image File System, UBIFS)是用于固态硬盘存储设备上，并与LogFS相互竞争，作为JFFS2的后继文件系统之一。真正开始开发于2007年，并于2008年10月第一次加入稳定版本于Linux核心2.6.27版。
UBIFS最早在2006年由IBM与Nokia的工程师Thomas Gleixner，Artem Bityutskiy所设计，专门为了解决MTD（Memory Technology Device）设备所遇到的瓶颈。由于Nand Flash容量的暴涨，YAFFS等皆无法再去控制Nand Flash的空间。UBIFS通过子系统UBI处理与MTD device之间的动作。与JFFS2一样，UBIFS 建构于MTD device 之上，因而与一般的block device不兼容。JFFS2运行在MTD设备之上，而UBIFS则只能工作于UBI volume之上。也可以说，UBIFS涉及了三个子系统：
1.MTD Subsystem：
MTD 子系统， 提供对flash芯片的访问接口， MTD子系统提供了MTD device的概念，比如/dev/mtdx，MTD可以认为是raw flash。
2.UBI subsystem：
为flash device提供了wear-leveling和 volume management功能； UBI工作在MTD设备之上，提供了UBI volume；UBI是MTD设备的高层次表示，对上层屏蔽了一些MTD不得不处理的问题，比如wearing以及坏块管理。3.UBIFS filesystem
UBIFS 文件系统，工作于UBI之上。
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mkfs.ubifs的用法
Usage: mkfs.ubifs[OPTIONS] target
Make a UBIFS file system image from an existing directorytree
Examples:
Build file system from directory /opt/img, writting the result inthe ubifs.img file
mkfs.ubifs -m 512 -e 128KiB -c 100 -r /opt/imgubifs.img
The same, but writting directly to an UBIvolume
mkfs.ubifs -r /opt/img/dev/ubi0_0
Creating an empty UBIFS filesystem on an UBIvolume
mkfs.ubifs/dev/ubi0_0
Options:
-r, -d, --root=DIR build file system fromdirectory DIR
-m, --min-io-size=SIZE minimum I/O unitsize，最小输入输出大小
-e, --leb-size=SIZE logicalerase block size逻辑可擦出块大小
-c, --max-leb-cnt=COUNT maximum logical erase blockcount最大逻辑可擦出块数目
-o, --output=FILE outputto FILE输出文件名
-j, --jrn-size=SIZE journalsize
-R, --reserved=SIZE howmuch space should be reserved for thesuper-user
-x, --compr=TYPE compressiontype - "lzo", "favor_lzo", "zlib" or
"none" (default:"lzo")
-X, --favor-percent may only be used with favor LZO compression anddefines
how many percentbetter zlib should compress to make
mkfs.ubifsuse zlib instead of LZO (default 20%)
-f, --fanout=NUM fanout NUM (default: 8)
-F, --space-fixup file-system free space has tobe fixed up on first moun
(requires kernel version 3.0 orgreater)
-k, --keyhash=TYPE key hash type - "r5" or "test" (default:"r5")
-p, --orph-lebs=COUNT countof erase blocks for orphans (default: 1)
-D, --devtable=FILE use device table FILE
-U, --squash-uids squash owners making allfiles owned by root
-l, --log-lebs=COUNT count of eraseblocks for the log (used onlyfor debugging)
-v, --verbose verbose operation
-V, --version display versioninformation
-g, --debug=LEVEL display debug information (0- none, 1 - statistics, 2 - files, 3 - moredetails)
-h, --help displaythis help text
例：
mkfs.ubifs -x lzo -m 2KiB -e 124KiB -c 720 -osystem_ubifs.img -d$path_to_system
压缩格式为lzo
-m最小输入输出大小为2KiB(2048bytes)，一般为页大小
-e逻辑可擦除块大小为124KiB=(每块的页数-2)*页大小=（64-2）*2KiB=124KiB
-c最多逻辑可擦除块数目为720(720*128KiB=90MiB),这个可根据ubivolume来设置，实际上是设置此卷的最大容量。
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ubinize的用法
Usage: ubinize [-ofilename] [-p ] [-m ] [-s ] [-O ] [-e
][-x ] [-Q ] [-v] [-h] [-V] [--output=]
[--peb-size=] [--min-io-size=] [--sub-page-size=]
[--vid-hdr-offset=] [--erase-counter=] [--ubi-ver=]
[--image-seq=] [--verbose] [--help] [--version]ini-file
Example: ubinize -o ubi.img -p 16KiB -m 512 -s 256 cfg.ini - createUBI image
'ubi.img' as described byconfiguration file'cfg.ini'
-o, --output= output filename
-p, --peb-size= size of the physical eraseblock of theflash
thisUBI image is created for in bytes,
kilobytes(KiB), or megabytes (MiB)
(mandatoryparameter)物理可擦出块大小
-m, --min-io-size= minimuminput/output unit size of the flash
inbytes
-s, --sub-page-size= minimum input/output unitused for UBI
headers,e.g. sub-page size in case of NAND
flash(equivalent to the minimum input/output
unitsize by default)子页大小
-O,--vid-hdr-offset= offset if the VID header fromstart of the
physicaleraseblock (default is the next
minimumI/O unit or sub-page after the EC
header)VID头部偏移量,默认是512
-e, --erase-counter= the erasecounter value to put to EC headers (default is0)
-x, --ubi-ver= UBIversion number to put to ECheaders (default is1)
-Q, --image-seq= 32-bit UBI image sequencenumber to use
(bydefault a random number is picked)
-v, --verbose beverbose
-h, --help printhelp message
-V, --version printprogram version
例：
ubinize –o ubi.img -m 2KiB -p 128KiB -s 2048$system_cfg_file –v
-m最小输入输出大小为2KiB(2048bytes)，一般为页大小
-p物理可擦出块大小为128KiB=每块的页数*页大小=64*2KiB=128KiB
-s用于UBI头部信息的最小输入输出单元，一般与最小输入输出单元(-m参数)大小一样。
ubinize需要指定一个配置文件$system_cfg_file，内容如下：
[rootfs-volume]
mode=ubi
image=system_ubifs.img
vol_id=0
vol_size=90MiB
vol_type=dynamic
vol_name=system
======================================================================
配置文件说明
INI-file format.
The input configuration ini-file describes all the volumes whichhave to
be included to the output UBI image. Each volume is described inits own
section which may be named arbitrarily. The section consistson
"key=value" pairs, for example:
[jffs2-volume]
mode=ubi
image=../jffs2.img mkfs.ubi生成的源镜像
vol_id=1 卷序号
vol_size=30MiB 卷大小
vol_type=dynamic 动态卷
vol_name=jffs2_volume 卷名
vol_flags=autoresize
vol_alignment=1
This exampleconfiguration file tells the utility to create an UBIimage with one volume with ID 1, volume size30MiB, the volume is dynamic, has name"jffs2_volume", "autoresize"
volume flag, and alignment 1.The "image=../jffs2.img" line tells the utility totake the contents of the volume from the"../jffs2.img" file. The size of the image file has tobe less or equivalent to the volume size (30MiB).The "mode=ubi" line
is mandatory and just tellsthat the section describes an UBI volume -other section modes may be added in thefuture.
Notes:
* size in vol_size might be specified kilobytes (KiB), megabytes(MiB), gigabytes (GiB) or bytes(no modifier);
* if "vol_size" key is absent, the volume sizeis assumed to be equivalent to the size of theimage file (defined by "image" key);
* if the "image" is absent, the volume isassumed to be empty;
* volume alignment must not be greater than the logical eraseblocksize;
* one ini file may contain arbitrary number ofsections, the utility will put all the volumeswhich are described by these section to the output UBI imagefile.
