Linux kernel, Android, Golang & Recsys

错误信息:

bvcom@ubuntu:~/tmp/AR6kSDK.2.2.1.180$ git push
Counting objects: 29, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (12/12), done.
Writing objects: 100% (15/15), 1.53 KiB, done.
Total 15 (delta 7), reused 0 (delta 0)
remote: error: refusing to update checked out branch: refs/heads/master
remote: error: By default, updating the current branch in a non-bare repository
remote: error: is denied, because it will make the index and work tree inconsistent
remote: error: with what you pushed, and will require ‘git reset –hard’ to match
remote: error: the work tree to HEAD.
remote: error:
remote: error: You can set ‘receive.denyCurrentBranch’ configuration variable to
remote: error: ‘ignore’ or ‘warn’ in the remote repository to allow pushing into
remote: error: its current branch; however, this is not recommended unless you
remote: error: arranged to update its work tree to match what you pushed in some
remote: error: other way.
remote: error:
remote: error: To squelch this message and still keep the default behaviour, set
remote: error: ‘receive.denyCurrentBranch’ configuration variable to ‘refuse’.
To git://192.168.2.212/AR6kSDK.2.2.1.180/.git
! [remote rejected] master -> master (branch is currently checked out)
error: failed to push some refs to ‘git://192.168.2.212/AR6kSDK.2.2.1.180/.git’

解决方法:
这是由于git默认拒绝了push操作，需要进行设置，修改.git/config添加如下代码：

[receive]
denyCurrentBranch = ignore

在初始化远程仓库时最好使用 git –bare init 而不要使用：git init
如果使用了git init初始化，则远程仓库的目录下，也包含work tree，当本地仓库向远程仓库push时, 如果远程仓库正在push的分支上（如果当时不在push的分支，就没有问题）, 那么push后的结果不会反应在work tree上, 也即在远程仓库的目录下对应的文件还是之前的内容，必须得使用git reset –hard才能看到push后的内容.

1. http://hi.baidu.com/wbo4958/blog/item/8613d68619b0522666096eff.html
2. http://hi.baidu.com/zkfarmer/blog/item/4a4bfd0899db95336a60fb42.html

–EOF–

在用vim的时候要经常搜索，但是有的时候会忘记＊和 # 这两个快捷键，所以记录如下

在通常模式下:

/ 向下查找

? 向上查找

* 向下查找当前光标下的单词

# 向上查找当前光标下的单词.

f{char} 跳到当前行,当前位置右边的{char}的位置. 如

using namespace std;

用f; 将会跳到;所在的位置.

F{char} 类似f{char},不过,是左边.

t{char} 类似f{char},不过,把光标放在{char}的前一个位置.

T{char} 类似t{char},不过,是左边.

; 重复t T f T 指令

, 朝相反方向重复t T f T 指令

–
Bian Jiang
Blog:  http://www.wifihack.net/

进来在作IGMP协议栈的解析，简单记录如下:

IGMPV3 Types

   There are two IGMP message types of concern to the IGMPv3 protocol
   described in this document:

      Type Number (hex)   Message Name
      -----------------   ------------

            0x11          Membership Query

            0x22          Version 3 Membership Report

   An implementation of IGMPv3 MUST also support the following three
   message types, for interoperation with previous versions of IGMP (see
   section 7):

           0x12          Version 1 Membership Report    [RFC-1112]

           0x16          Version 2 Membership Report    [RFC-2236]

IGMP V1 Query:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |Version| Type  |    Unused     |           Checksum            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Group Address                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

IGMP V2 Query:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Type     | Max Resp Time |           Checksum            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Group Address                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

IGMP V3 Membership Query Message: :

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Type = 0x11  | Max Resp Code |           Checksum            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Group Address                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Resv  |S| QRV |     QQIC      |     Number of Sources (N)     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Source Address [1]                      |
      +-                                                             -+
      |                       Source Address [2]                      |
      +-                              .                              -+
      .                               .                               .
      .                               .                               .
      +-                                                             -+
      |                       Source Address [N]                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 Version 3 Membership Report Message

   Version 3 Membership Reports are sent by IP systems to report (to
   neighboring routers) the current multicast reception state, or
   changes in the multicast reception state, of their interfaces.
   Reports have the following format:

RFC 3376                         IGMPv3                     October 2002

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Type = 0x22  |    Reserved   |           Checksum            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           Reserved            |  Number of Group Records (M)  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      .                                                               .
      .                        Group Record [1]                       .
      .                                                               .
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      .                                                               .
      .                        Group Record [2]                       .
      .                                                               .
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                               .                               |
      .                               .                               .
      |                               .                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      .                                                               .
      .                        Group Record [M]                       .
      .                                                               .
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where each Group Record has the following internal format:

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Record Type  |  Aux Data Len |     Number of Sources (N)     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Multicast Address                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Source Address [1]                      |
      +-                                                             -+
      |                       Source Address [2]                      |
      +-                                                             -+
      .                               .                               .
      .                               .                               .
      .                               .                               .
      +-                                                             -+
      |                       Source Address [N]                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      .                                                               .
      .                         Auxiliary Data                        .
      .                                                               .
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Example:
Version 3 Membership Report Message
 22 00 ea 03     | Type: 22, Checksum: ea 03
 00 00 00 01     | Number of group recode 01
 04 00 00 00     | Recode type: 04, Number of Sources: 00 00
 ef ff ff fa      | Multicast Addr: 239.255.255.250

 Group Record Types

   There are a number of different types of Group Records that may be
   included in a Report message:

   o A "Current-State Record" is sent by a system in response to a Query
     received on an interface.  It reports the current reception state
     of that interface, with respect to a single multicast address.  The
     Record Type of a Current-State Record may be one of the following
     two values:

        Value  Name and Meaning
        -----  ----------------

          1    MODE_IS_INCLUDE - indicates that the interface has a
               filter mode of INCLUDE for the specified multicast
               address.  The Source Address [i] fields in this Group
               Record contain the interface's source list for the
               specified multicast address, if it is non-empty.

          2    MODE_IS_EXCLUDE - indicates that the interface has a
               filter mode of EXCLUDE for the specified multicast
               address.  The Source Address [i] fields in this Group
               Record contain the interface's source list for the
               specified multicast address, if it is non-empty.

   o A "Filter-Mode-Change Record" is sent by a system whenever a local
     invocation of IPMulticastListen causes a change of the filter mode
     (i.e., a change from INCLUDE to EXCLUDE, or from EXCLUDE to
     INCLUDE), of the interface-level state entry for a particular
     multicast address.  The Record is included in a Report sent from
     the interface on which the change occurred.  The Record Type of a
     Filter-Mode-Change Record may be one of the following two values:

          3    CHANGE_TO_INCLUDE_MODE - indicates that the interface
               has changed to INCLUDE filter mode for the specified
               multicast address.  The Source Address [i] fields
               in this Group Record contain the interface's new
               source list for the specified multicast address,
               if it is non-empty.

          4    CHANGE_TO_EXCLUDE_MODE - indicates that the interface
               has changed to EXCLUDE filter mode for the specified
               multicast address.  The Source Address [i] fields
               in this Group Record contain the interface's new
               source list for the specified multicast address,
               if it is non-empty.

   o A "Source-List-Change Record" is sent by a system whenever a local
     invocation of IPMulticastListen causes a change of source list that
     is *not* coincident with a change of filter mode, of the
     interface-level state entry for a particular multicast address.
     The Record is included in a Report sent from the interface on which
     the change occurred.  The Record Type of a Source-List-Change
     Record may be one of the following two values:

          5    ALLOW_NEW_SOURCES - indicates that the Source Address
               [i] fields in this Group Record contain a list of the
               additional sources that the system wishes to
               hear from, for packets sent to the specified
               multicast address.  If the change was to an INCLUDE
               source list, these are the addresses that were added
               to the list; if the change was to an EXCLUDE source
               list, these are the addresses that were deleted from
               the list.

          6    BLOCK_OLD_SOURCES - indicates that the Source Address
               [i] fields in this Group Record contain a list of the
               sources that the system no longer wishes to
               hear from, for packets sent to the specified
               multicast address.  If the change was to an INCLUDE
               source list, these are the addresses that were
               deleted from  the list; if the change was to an
               EXCLUDE source list, these are the addresses that
               were added to the list.

   If a change of source list results in both allowing new sources and
   blocking old sources, then two Group Records are sent for the same
   multicast address, one of type ALLOW_NEW_SOURCES and one of type
   BLOCK_OLD_SOURCES.

IGMP Query



IGMP Report



图来自  Linux Networking Architecture 17.3.4 Implementing IGMP

参考:
1. IGMPV1 rfc1112
2. IGMPV2 rfc2236
3. IGMPV3 rfc3376
4. Linux下IGMP以及多播路由分析
5. Design and Implementation of IGMPv3 for Linux (2000)  
6. Linux Kernel 2.6.26
7. 在线查看Kernel: http://lxr.linux.no/linux+v2.6.26/
8.  RFC3376 因特网组管理协议 第3版(译)
9.  Linux Networking Architecture (Chapter 17. IP Multicast for Group Communication)
10. Mapping IP Multicast to MAC-Layer Multicast 

之前使用Graphviz生成了一张mongoose的函数调用图，这里将讲是怎么生成的。

通过Graphvis生成mongoose的函数调用关系
基本的理论可以参考这里(http://www.ibm.com/developerworks/cn/linux/l-graphvis/), 思路如下:
1. 通过GCC的 -finstrument-functions 和 -g 选项，获得函数调用关系的地址.
2. 使用 Addr2line 将函数地址解析为函数名.
3. 精简函数跟踪数据(可以参考pvtrace, http://download.boulder.ibm.com/ibmdl/pub/software/dw/library/l-graphvis/pvtrace.zip)
4. 使用Graphvis生成图片.

具体的步骤:
1. 在我们编译mongoose的时候，加上 instrument.c 文件。
instrument.c 文件的作用是在我们执行文件的时候，会自动记录函数入口和出口的函数地址，并保存在当前目录下面的trace.txt文件里面。 注意: 在用gcc编译的时候一定要加 -finstrument-functions 和 -g 参数。

在mongoose的Makefile文件中增加instrument.c文件。
原文：

$(CC) $(LINFLAGS) mongoose.c main.c -s -o $(PROG)

改为:

$(CC) $(LINFLAGS) instrument.c mongoose.c  main.c -finstrument-functions -g -s -o $(PROG)

2. 编译mongoose.
make linux

3. 运行编译好的mongoose程序，并在当前目录生成一个trace.txt 文件。

3. 下载 pvtrace.zip 并编译。
回生成一个pvtrace程序，这个程序主要是从trace.txt和mongoose中提取函数地址对应的函数名，并生成graphivz的语法树。

4. 使用你编译好的文件pvtrace, 运行mongoose, 来获得graph.dot文件。

5. 使用Graph程序，生成图片, 前提是你必须安装graphivz
Debian/Ubuntu

sudo apt-get install graphviz.

安装完后运行:

dot -Tjpg graph.dot -o graph.jpg

6. Over.
效果图参考: http://wifihack.net/blog/2009/04/mongoose-start-function-call-use-graph/

instrument.c:

/********************************************************************
* File: instrument.c
*
* Instrumentation source — link this with your application, and
*  then execute to build trace data file (trace.txt).
*
* Author: M. Tim Jones <mtj@mtjones.com>
*
*/

#include <stdio.h>
#include <stdlib.h>

/* Function prototypes with attributes */
void main_constructor( void )
__attribute__ ((no_instrument_function, constructor));

void main_destructor( void )
__attribute__ ((no_instrument_function, destructor));

void __cyg_profile_func_enter( void *, void * )
__attribute__ ((no_instrument_function));

void __cyg_profile_func_exit( void *, void * )
__attribute__ ((no_instrument_function));

static FILE *fp;

void main_constructor( void )
{
fp = fopen( “trace.txt”, “w” );
if (fp == NULL) exit(-1);
}

void main_deconstructor( void )
{
fclose( fp );
}

void __cyg_profile_func_enter( void *this, void *callsite )
{
fprintf(fp, “E%p\n”, (int *)this);
}

void __cyg_profile_func_exit( void *this, void *callsite )
{
fprintf(fp, “X%p\n”, (int *)this);
}

Ref:
1. 用 Graphviz 可视化函数调用 http://www.ibm.com/developerworks/cn/linux/l-graphvis/

–EOF–

mongoose start function call use graph

I constructed a mongoose start function call use graphviz.

Links:

1.   Visualize function calls with Graphviz http://www.ibm.com/developerworks/library/l-graphvis/