月份：2015年10月

virt-manager/virsh调试技巧（不断更新）

（1）使用virt-manager --trace-libvirt --debug可以输出virt-manager的调试信息。

Linux:~ # virt-manager --trace-libvirt --debug
[Thu, 22 Oct 2015 13:54:08 virt-manager 6124] DEBUG (cli:246) Launched with command line: /usr/share/virt-manager/virt-manager --trace-libvirt --debug
[Thu, 22 Oct 2015 13:54:08 virt-manager 6124] DEBUG (virt-manager:153) virt-manager version: 1.2.1
[Thu, 22 Oct 2015 13:54:08 virt-manager 6124] DEBUG (virt-manager:154) virtManager import: <module 'virtManager' from '/usr/share/virt-manager/virtManager/__init__.pyc'>
[Thu, 22 Oct 2015 13:54:08 virt-manager 6124] DEBUG (virt-manager:157) Libvirt tracing requested
[Thu, 22 Oct 2015 13:54:08 virt-manager 6124] DEBUG (module_trace:66) wrapfunc <function _dispatchEventHandleCallback at 0x7ff4391fc050> _dispatchEventHandleCallback
[Thu, 22 Oct 2015 13:54:08 virt-manager 6124] DEBUG (module_trace:66) wrapfunc <function _dispatchEventTimeoutCallback at 0x7ff4391fc0c8> _dispatchEventTimeoutCallback
[Thu, 22 Oct 2015 13:54:08 virt-manager 6124] DEBUG (module_trace:66) wrapfunc <function _eventInvokeHandleCallback at 0x7ff439251ed8> _eventInvokeHandleCallback
[Thu, 22 Oct 2015 13:54:08 virt-manager 6124] DEBUG (module_trace:66) wrapfunc <function _eventInvokeTimeoutCallback at 0x7ff439251f50> _eventInvokeTimeoutCallback
......

也可以重定向输出到文件：

Linux:~ # virt-manager --trace-libvirt --debug > log.txt 2>&1

（2）通过virsh输出Guest OS日志：

Linux:~ # virsh
Welcome to virsh, the virtualization interactive terminal.

Type:  'help' for help with commands
       'quit' to quit

virsh # list
 Id    Name                           State
----------------------------------------------------
 0     Domain-0                       running
 3     sles11sp4-i686                 running

virsh # console 3
Connected to domain sles11sp4-i686
Escape character is ^]
[    0.000000] Reserving virtual address space above 0xf5800000
[    0.000000] Initializing cgroup subsys cpuset
[    0.000000] Initializing cgroup subsys cpu
[    0.000000] Linux version 3.0.101-63-xen (geeko@buildhost) (gcc version 4.3.4 [gcc-4_3-branch revision 152973] (SUSE Linux) ) #1 SMP Tue Jun 23 16:02:31 UTC 2015 (4b89d0c)
......

 

libvirt和virt-manager简介

libvirt提供了一个用来管理虚拟机的抽象层。它包含如下部分：一组C API；各种编程语言的绑定；一个daemon进程（libvirtd）和一个命令行工具（virsh）。结构如下图所示：

Capturevirt-manager是一个管理虚拟机的图形化工具，它类似于VirtualBox。另外，virt-manager还提供了virt-clone等命令行工具。

 

SLES和SLES SP的区别

今天才知道SLES（SUSE Linux Enterprise Server）和SLES SP（SUSE Linux Enterprise Server Service Package）是不同的版本，SLES相当于主版本（major version），而SLES SP则相当于基于主版本发布的小版本（minor version）。参见wiki百科：

SUSE Linux Enterprise Server (SLES) is a Linux-based operating system developed by SUSE. It is designed for servers, mainframes, and workstations but can be installed on desktop computers for testing as well. Major versions are released at an interval of 3–4 years, while minor versions (called “Service Packs”) are released about every 18 months. SUSE Linux Enterprise products, including SUSE Linux Enterprise Server, receive more intense testing than the openSUSE community product, with the intention that only mature, stable versions of the included components will make it through to the released enterprise product. SLES 11 SP4 was released July 16th, 2015, which is developed from a common code base with SUSE Linux Enterprise Desktop and other SUSE Linux Enterprise products.

查看SLES发行版信息：

linux-6fj5:/ # cat /etc/issue

Welcome to SUSE Linux Enterprise Server 11 SP4  (x86_64) - Kernel \r (\l).

Linux kernel 笔记 （33）——“debugfs“简介

以下摘自维基百科：

debugfs is a simple to use RAM-based file system specially designed for debugging purposes. It exists as a simple way for kernel developers to make information available to user space. Unlike /proc, which is only meant for information about a process, or sysfs, which has strict one-value-per-file rules, debugfs has no rules at all. Developers can put any information they want there.

debugfs是一个用于调试目的，简单的，基于内存的文件系统。kernel的信息可以输出到debugfs中，这样方便user space程序查看和使用。

为了使用debugfs功能，编译kernel时需要把CONFIG_DEBUG_FS置成yes。

典型的挂载debugfs文件系统命令：

mount -t debugfs none /sys/kernel/debug

由于没有具体设备，所以设备的位置使用了none（参考这个帖子）

 

Lua笔记（24）—— tonumber和tostring

尽管Lua会提供数字和字符串之间的自动转换：

> print("10" + 30)
40
> print(10 .. 30)
1030

为了使程序的可读性更好，可以考虑使用显示转换：

> print(tonumber("10") + 30)
40
> print(tostring(10) .. tostring(30))
1030

tonumber把字符串转换为数字，而tostring则把数字转换为字符串。

另外，把数字和空字符串连接起来，也可以达到tostring的效果：

> print(type(10 .. ""))
string

 

Virtualization的几种解决方案

（1）Binary writing

Binary writing has the nice benefit that it allows most of the virtual environment to run in userspace, but imposes a performance penalty.
The binary rewriting approach requires that the instruction stream be scanned by the virtualization environment and privileged instructions identified. These are then rewritten to point to their emulated versions.

Binary writing的核心之处在于把privileged instructions重写。

（2）Paravirtualization

Rather than dealing with problematic instructions, paravirtualization systems like Xen simply ignore them.

If a guest system executes an instruction that doesn’t trap while inside a paravirtualized environment, then the guest has to deal with the consequences. Conceptually, this is similar to the binary rewriting approach, except that the rewriting happens at compile time (or design time), rather than at runtime.

The environment presented to a Xen guest is not quite the same as that of a real x86 system. It is sufficiently similar, however, in that it is usually a fairly simple task to port an operating system to Xen.

From the perspective of an operating system, the biggest difference is that it runs in ring 1 on a Xen system, instead of ring 0. This means that it cannot perform any privileged instructions. In order to provide similar functionality, the hypervisor exposes a set of hypercalls that correspond to the instructions.

 

Capture

Paravirtualization核心之处在于hypervisor提供hypercalls给Guest OS，以弥补其不能使用privileged instructions。

（3）Hardware-Assisted Virtualization

Now, both Intel and AMD have added a set of instructions that makes virtualization considerably easier for x86. AMD introduced AMD-V, formerly known as Pacifica, whereas Intel’s extensions are known simply as (Intel) Virtualization Technology (IVT or VT). The idea behind these is to extend the x86 ISA to make up for the shortcomings in the existing instruction set. Conceptually, they can be thought of as adding a “ring -1” above ring 0, allowing the OS to stay where it expects to be and catching attempts to access the hardware directly. In implementation, more than one ring is added, but the important thing is that there is an extra privilege mode where a hypervisor can trap and emulate operations that would previously have silently failed.

IVT adds a new mode to the processor, called VMX. A hypervisor can run in VMX mode and be invisible to the operating system, running in ring 0. When the CPU is in VMX mode, it looks normal from the perspective of an unmodified OS. All instructions do what they would be expected to, from the perspective of the guest, and there are no unexpected failures as long as the hypervisor correctly performs the emulation.

A set of extra instructions is added that can be used by a process in VMX root mode. These instructions do things like allocating a memory page on which to store a full copy of the CPU state, start, and stop a VM. Finally, a set of bitmaps is defined indicating whether a particular interrupt, instruction, or exception should be passed to the virtual machine’s OS running in ring 0 or by the hypervisor running in VMX root mode.

Hardware-Assisted Virtualization（也称之为HVM，Hardware Virtual Machine），可以运行unmodified OS，其核心之处在于CPU层面提供了新的privilege mode和指令集来支持虚拟化。

参考资料：
The Definitive Guide to the Xen Hypervisor。

Linux kernel 笔记 （32）——“make“和”make modules“

以下摘自LKD:

After the kernel configuration is set—however you do it—you can build it with a single command:
$ make
Unlike kernels before 2.6, you no longer need to run make dep before building the kernel—the dependency tree is maintained automatically.You also do not need to specify a specific build type, such as bzImage, or build modules separately, as you did in old versions.The default Makefile rule will handle everything.

也就是在2.6版本以后的Linux kernel中，执行make或make all命令即包含了make modules。也可参加这个帖子。

 

Linux kernel 笔记 （31）——“make help”命令

make help命令列出编译kernel时的选项帮助信息：

linux-4cy8:/usr/src/linux/build # make help
make -C /usr/src/linux-3.0.101-63 O=/usr/src/linux-3.0.101-63/build/. help
Cleaning targets:
  clean           - Remove most generated files but keep the config and
                    enough build support to build external modules
  mrproper        - Remove all generated files + config + various backup files
  distclean       - mrproper + remove editor backup and patch files

Configuration targets:
  config          - Update current config utilising a line-oriented program
  nconfig         - Update current config utilising a ncurses menu based program
  menuconfig      - Update current config utilising a menu based program
  xconfig         - Update current config utilising a QT based front-end
  gconfig         - Update current config utilising a GTK based front-end
  oldconfig       - Update current config utilising a provided .config as base
  localmodconfig  - Update current config disabling modules not loaded
  localyesconfig  - Update current config converting local mods to core
  silentoldconfig - Same as oldconfig, but quietly, additionally update deps
  defconfig       - New config with default from ARCH supplied defconfig
  savedefconfig   - Save current config as ./defconfig (minimal config)
  allnoconfig     - New config where all options are answered with no
  allyesconfig    - New config where all options are accepted with yes
  allmodconfig    - New config selecting modules when possible
  alldefconfig    - New config with all symbols set to default
  randconfig      - New config with random answer to all options
  listnewconfig   - List new options
  oldnoconfig     - Same as silentoldconfig but set new symbols to n (unset)

Other generic targets:
  all             - Build all targets marked with [*]
* vmlinux         - Build the bare kernel
* modules         - Build all modules
  modules_install - Install all modules to INSTALL_MOD_PATH (default: /)
  firmware_install- Install all firmware to INSTALL_FW_PATH
                    (default: $(INSTALL_MOD_PATH)/lib/firmware)
  dir/            - Build all files in dir and below
  dir/file.[oisS] - Build specified target only
  dir/file.lst    - Build specified mixed source/assembly target only
                    (requires a recent binutils and recent build (System.map))
  dir/file.ko     - Build module including final link
  modules_prepare - Set up for building external modules
  tags/TAGS       - Generate tags file for editors
  cscope          - Generate cscope index
  gtags           - Generate GNU GLOBAL index
  kernelrelease   - Output the release version string
  kernelversion   - Output the version stored in Makefile
  headers_install - Install sanitised kernel headers to INSTALL_HDR_PATH
                    (default: /usr/src/linux-3.0.101-63/build/usr)

Static analysers
  checkstack      - Generate a list of stack hogs
  namespacecheck  - Name space analysis on compiled kernel
  versioncheck    - Sanity check on version.h usage
  includecheck    - Check for duplicate included header files
  export_report   - List the usages of all exported symbols
  headers_check   - Sanity check on exported headers
  headerdep       - Detect inclusion cycles in headers
  coccicheck      - Check with Coccinelle.

Kernel packaging:
  rpm-pkg             - Build both source and binary RPM kernel packages
  binrpm-pkg          - Build only the binary kernel package
  deb-pkg             - Build the kernel as an deb package
  tar-pkg             - Build the kernel as an uncompressed tarball
  targz-pkg           - Build the kernel as a gzip compressed tarball
  tarbz2-pkg          - Build the kernel as a bzip2 compressed tarball
  tarxz-pkg           - Build the kernel as a xz compressed tarball
  perf-tar-src-pkg    - Build perf-3.0.101.tar source tarball
  perf-targz-src-pkg  - Build perf-3.0.101.tar.gz source tarball
  perf-tarbz2-src-pkg - Build perf-3.0.101.tar.bz2 source tarball
  perf-tarxz-src-pkg  - Build perf-3.0.101.tar.xz source tarball

Documentation targets:
 Linux kernel internal documentation in different formats:
  htmldocs        - HTML
  pdfdocs         - PDF
  psdocs          - Postscript
  xmldocs         - XML DocBook
  mandocs         - man pages
  installmandocs  - install man pages generated by mandocs
  cleandocs       - clean all generated DocBook files

Architecture specific targets (x86):
* bzImage      - Compressed kernel image (arch/x86/boot/bzImage)
  install      - Install kernel using
                  (your) ~/bin/installkernel or
                  (distribution) /sbin/installkernel or
                  install to $(INSTALL_PATH) and run lilo
  fdimage      - Create 1.4MB boot floppy image (arch/x86/boot/fdimage)
  fdimage144   - Create 1.4MB boot floppy image (arch/x86/boot/fdimage)
  fdimage288   - Create 2.8MB boot floppy image (arch/x86/boot/fdimage)
  isoimage     - Create a boot CD-ROM image (arch/x86/boot/image.iso)
                  bzdisk/fdimage*/isoimage also accept:
                  FDARGS="..."  arguments for the booted kernel
                  FDINITRD=file initrd for the booted kernel

  i386_defconfig           - Build for i386
  x86_64_defconfig         - Build for x86_64

  make V=0|1 [targets] 0 => quiet build (default), 1 => verbose build
  make V=2   [targets] 2 => give reason for rebuild of target
  make O=dir [targets] Locate all output files in "dir", including .config
  make C=1   [targets] Check all c source with $CHECK (sparse by default)
  make C=2   [targets] Force check of all c source with $CHECK
  make W=n   [targets] Enable extra gcc checks, n=1,2,3 where
                1: warnings which may be relevant and do not occur too often
                2: warnings which occur quite often but may still be relevant
                3: more obscure warnings, can most likely be ignored
                Multiple levels can be combined with W=12 or W=123
  make RECORDMCOUNT_WARN=1 [targets] Warn about ignored mcount sections

Execute "make" or "make all" to build all targets marked with [*]
For further info see the ./README file

很有用！！