qemu-img

参考：

https://wiki.archlinux.org/title/QEMU#Tips_and_tricks

https://qemu.readthedocs.io/en/latest/tools/qemu-img.html

禁止使用 qemu-img 修改正常运行的 VM 的 disk image

qemu-img用于生成hard disk imag(模拟的虚拟磁盘)，file format不同生成的hard disk image 不同

ENBF

FILENAME := is a disk image filename

FMT := is the disk image format. It is guessed automatically in most cases. See below for a description of the supported disk formats

SIZE := is the disk image size in  bytes.  Optional  suffixes  k  or  K (kilobyte,  1024)  M (megabyte, 1024k) and G (gigabyte, 1024M) and T (terabyte, 1024G) are supported.  b is ignored.

OUTPUT_FILENAME := is the destination disk image filename.

OUTPUT_FMT := is the destination format.

OPTIONS := is a comma separated list of format specific  options  in  a name=value format. Use -o ? for an overview of the options supported by the used format or see the format descriptions below for details.

SNAPSHOT_PARAM := is param used for internal snapshot, format is 'snapshot.id=[ID],snapshot.name=[NAME]' or '[ID_OR_NAME]'

Optional Args

-h

with or without a command, shows help and lists the supported formats
-p

display progress bar
-q

quiet mode - do not print any output
-S SIZE

指定 qemu-img create 生成的 disk image 大小。如果没有suffix，默认使用byte
--object OBJECTDEF

Positional Args

只介绍几个commands，具体可以查看 man page

create

syntax： create [--object OBJECTDEF] [-q] [-f FMT] [-b BACKING_FILE [-F BACKING_FMT]] [-u] [-o OPTIONS] FILENAME [SIZE]

cearte the new disk image FILENAME of size SIZE and format FMT

cpl in ~/software/kvm λ qemu-img create -f qcow2 win.img 100M
Formatting 'win.img', fmt=qcow2 size=104857600 cluster_size=65536 lazy_refcounts=off refcount_bits=16

-f FMT

生成的 disk image 格式
-b BACKING_FILE

只会记录与 BACKING_FILE 之间的 differ

也可以对现有的disk image进行备份(只有qcow2才支持)

#qemu-img create -f qcow2 -o backing_file=src,backing_fmt=src_fmt bak_file

cpl in /sharing/vm λ qemu-img create -f qcow2 -o backing_file=raw,backing_fmt=raw raw.bak
Formatting 'raw.bak', fmt=qcow2 cluster_size=65536 extended_l2=off compression_type=zlib size=10485760 backing_file=raw backing_fmt=raw lazy_refcounts=off refcount_bits=16

具体支持的options，查看qemu-img note章节

amend

syntax： amend [--object OBJECTDEF] [--image-opts] [-p] [-q] [-f FMT] [-t CACHE] [--force] -o OPTIONS FILENAME

Amends the image format specific OPTIONS for the image file FILENAME. Not all file formats support this operation

bench

syntax：bench [-c COUNT] [-d DEPTH] [-f FMT] [--flush-interval=FLUSH_INTERVAL] [-i AIO] [-n] [--no-drain] [-o OFFSET] [--pattern=PATTERN] [-q] [-s BUFFER_SIZE] [-S STEP_SIZE] [-t CACHE] [-w] [-U] FILENAME

run a simple sequential I/O benchmark on the specified image. If -w is specified, a write test is performed, otherwise a read test is performed

➜  ISO qemu-img bench -c 10 -d 10 -s 1M win.img -w
Sending 10 write requests, 1048576 bytes each, 10 in parallel (starting at offset 0, step size 1048576)
Run completed in 0.005 seconds.

-c COUNT

会执行 COUNT 次 IO 请求，
-s BUFFER_SIZE

每次IO请求 BUFFER_SIZE byte，
-d DEPTH

IO请求时，DEPTH 个并发线程
--flush-interval=FLUSH_INTERVAL

FLUSH_INTERVAL 会在新请求前清空磁盘

check

syntax：check [--object OBJECTDEF] [--image-opts] [-q] [-f FMT] [--output=OFMT] [-r [leaks | all]] [-T SRC_CACHE] [-U] FILENAME

Perform a consistency check on the edisk image FILENAME. only the formats qcow2, qed, parallels, vhdx, vmdk and vdi support consistency checks

➜  ISO qemu-img check --output json win.img
{
    "image-end-offset": 262144,
    "total-clusters": 1600,
    "check-errors": 0,
    "filename": "win.img",
    "format": "qcow2"
}

check-errors 通常包括如下几种状态码

0

check completed, the image is now consistent
1

check not completed because of internal errors
2

check completed, image is corrupted
64

checks are not supported by the image format

--output

指定输出的格式，可以是 human 或者 json
-r [leaks | all]

qemu-img tries to repair any inconsistencies found during the check，-r leaks repairs only cluster leaks, whereas -r all fixes all kinds of errors, with a higher risk of choosing the wrong fix or hiding corruption that has already occurred

snapshot

syntax：snapshot`` [--object OBJECTDEF] [--image-opts] [-U] [-q] [-l | -a SNAPSHOT | -c SNAPSHOT | -d SNAPSHOT] FILENAME

-a

回滚到某一快照
-c

生成快照
-d

删除快照
-l

显示image所有的快照

compare

syntax：compare [--object OBJECTDEF] [--image-opts] [-f FMT] [-F FMT] [-T SRC_CACHE] [-p] [-q] [-s] [-U] FILENAME1 FILENAME2

check if two images have the same content

➜  ISO qemu-img compare win.img win2.img 
Images are identical.

包含如下几种退出值

0

images are identical
1

iamges differ
2

error on opening an image
3

error on checking a sector allocation
4

error on reading data

-f

first image format
-F

second image format

dd

syntax：dd [--image-opts] [-U] [-f FMT] [-O OUTPUT_FMT] [bs=BLOCK_SIZE] [count=BLOCKS] [skip=BLOCKS] if=INPUT of=OUTPUT

dd copies from INPUT file to OUTPUT file coverting it from FMT format to OUTPUT_FMT

和 linux dd 类似，可以替代 convert 的部分功能

bs=BLOCK_SIZE

define the block size
count=BLOCKS

sets the number of input blocks to copy
if=INPUT

sets the input file
of=OUTPUT

sets the output file
skip=BLOCKS

sets the number of input blocks to skip

info

syntax：info [--object OBJECTDEF] [--image-opts] [-f FMT] [--output=OFMT] [--backing-chain] [-U] FILENAME

give information about the disk image FILENAME.

cpl in ~/software/kvm λ qemu-img info win.img 
image: win.img
file format: qcow2
virtual size: 100 MiB (104857600 bytes)
disk size: 196 KiB
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: false
    refcount bits: 16
    corrupt: false

resize

syntax：qemu-img resize [-f fmt] [--shrink] <filename> [+|- ]size

修改disk image的大小，如果需要缩小必须使用--shrink(需要先修改虚拟机中的分区和file system，否则数据会丢失)

cpl in ~/software/kvm λ qemu-img resize win.img +10M
Image resized.

修改完后需要进入虚拟机修改file system

rebase

syntax：rebase [--object OBJECTDEF] [--image-opts] [-U] [-q] [-f FMT] [-t CACHE] [-T SRC_CACHE] [-p] [-u] -b BACKING_FILE [-F BACKING_FMT] FILENAME

changing the backing file of an image. only the formats qcow2 and qed support changing the backing file

convert

syntax： convert [--object OBJECTDEF] [--image-opts] [--target-image-opts] [--target-is-zero] [--bitmaps [--skip-broken-bitmaps]] [-U] [-C] [-c] [-p] [-q] [-n] [-f FMT] [-t CACHE] [-T SRC_CACHE] [-O OUTPUT_FMT] [-B BACKING_FILE [-F BACKING_FMT]] [-o OPTIONS] [-l SNAPSHOT_PARAM] [-S SPARSE_SIZE] [-r RATE_LIMIT] [-m NUM_COROUTINES] [-W] FILENAME [FILENAME2 [...]] OUTPUT_FILENAME

Convert the disk image FILENAME or a snapshot SNAPSHOT_PARAM to disk image OUTPUT_FILENAME using format OUTPUT_FMT

➜  ISO qemu-img convert -f qcow2 -O raw t1.img t1.raw
➜  ISO qemu-img info t1.raw
image: t1.raw
file format: raw
virtual size: 100 MiB (104857600 bytes)
disk size: 4 KiB

-f

输入 image 的格式
-O

希望转成的目标格式
-c

compressed，将 OUTPUT_FLIENAME 压缩，只有 qcow 和 qcow2 支持
-B

force the output image to be created as a copu on write image of the specifed base image
-W

如果多线程处理器，可以加速处理

Formats

qemu支持的file format有如下几种类型

raw

==默认使用的类型==，可以将这种格式的 image file导入到其他的emulators。如果OS支持ext2或者ext3 on Linux or NTFS on windows。只有实际使用的扇区占用实际的物理磁盘空间。可以使用 qemu-img info 来查看实际占用的物理磁盘空间或者是用ls -ls

支持的选项：
- preallocation
  
  支持如下几个值（off, falloc, full）。其中 full 表示直接分配实际的大小
qcow2

生成的镜像更小，常常用在不支持linux fs的系统(例如windows)。只有虚拟机往扇区中写时才会实际分配。如果使用这种方式替代raw类型的disk image 可能会造成性能上的影响
```
cpl in /sharing/vm λ qemu-img create -f raw raw 10M    
Formatting 'raw', fmt=raw size=10485760
cpl in /sharing/vm λ qemu-img create -f qcow2 qcow2 10M
Formatting 'qcow2', fmt=qcow2 cluster_size=65536 extended_l2=off compression_type=zlib size=10485760 lazy_refcounts=off refcount_bits=16
cpl in /sharing/vm λ ll
.rw-r--r-- cpl cpl 192 KB Wed Jun  2 18:11:00 2021  qcow2
.rw-r--r-- cpl cpl  10 MB Wed Jun  2 18:10:55 2021  raw
```
支持的选项：
- compat
  
  版本控制参数，具体查看man page
- backing_file
  
  filename of a base image
- backing_fmt
  
  image format of the base image
- encryption
  
  use 128 bit AES-CBC encryption on the image
- preallocation
- data_file
  
  filename where all guest data will be stored. If this option is used, the qcow2 file will only contain the image’s metadata
  
  Note: data loss will occur if the given filename already exists when using this option with qemu-img creat since qemu-img will create the data file anew, overwriting the file anew overwriting the file’s original contents
other

包括其他一些兼容的格式，例如VMDK，VDI，VHD，qcow1和QED等

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qemu-img.md

qemu-img.md

qemu-img

ENBF

Optional Args

Positional Args

create

amend

bench

check

snapshot

compare

dd

info

resize

rebase

convert

Formats

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qemu-img.md

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qemu-img

ENBF

Optional Args

Positional Args

create

amend

bench

check

snapshot

compare

dd

info

resize

rebase

convert

Formats