ubuntu 13.04英文版裝中文輸入(注音)

apt-get install scim-chewing scim-modules-table
System Settings > Language Support > Install / Remove Languages… 選Chinese

System Settings > Language Support > keyboard input method system 選SCIM

接著啟動SCIM刪除不必要的輸入法


增加切換下一個輸入法的組合鍵

RFC 5952 - A Recommendation for IPv6 Address Text Representation 之筆記

1. Introduction

RFC 5952主要在定義IPv6 address的表示法的標準化，主要原因是因為RFC 4291 - IP Version 6 Addressing Architecture定義了IPv6 address，且提供了一些彈性表示法，卻也因為彈性導致相同的address卻有不同的表示法(換言之，不同的表示法卻是指向同一address)，這會導致一些問題產生。

以下的IPv6 address都是相同的：

2001:db8:0:0:1:0:0:1
2001:0db8:0:0:1:0:0:1 
2001:db8::1:0:0:1
2001:db8::0:1:0:0:1 
2001:0db8::1:0:0:1
2001:db8:0:0:1::1 
2001:db8:0000:0:1::1
2001:DB8:0:0:1::1 

2. Text Representation Flexibility of RFC 4291

2.1. Leading Zeros in a 16-Bit Field
'It is not necessary to write the leading zeros in an individual field.'
以0為開頭的字沒必要寫，因為這樣，所以0開頭的字母可寫可不寫，如：

2001:db8:aaaa:bbbb:cccc:dddd:eeee:0001
2001:db8:aaaa:bbbb:cccc:dddd:eeee:001
2001:db8:aaaa:bbbb:cccc:dddd:eeee:01
2001:db8:aaaa:bbbb:cccc:dddd:eeee:1

2.2. Zero Compression
'A special syntax is available to compress the zeros. The use of "::" indicates one or more groups of 16 bits of zeros.'
'The "::" can only appear once in an address.'
可以將1個或多個的"0000"用::這個特殊寫法表示，不過只能出現一次如：

2001:db8:0:0:0::1
2001:db8:0:0::1
2001:db8:0::1
2001:db8::1

2.3. Uppercase or Lowercase
RFC 4291並沒有特別指明說要用大寫或小寫表示之。

3. Problems Encountered with the Flexible Model

簡單來說，就是比對會有問題，比如對eth0指定IPv6網址2001:db8:0:0:1::1，之後用ifconfig eth0| grep 來找卻找不到，因為ifconfig顯示的是2001:db8::1:0:0:1這個IPv6 address。大小寫的差異在UNIX系統更是常見，比如2001:db8:0:0:1:0:0:1和2001:DB8:0:0:1:0:0:1在比對沒有特別指明case insensitive參數就會視為不同。

4. A Recommendation for IPv6 Text Representation

4.1. Handling Leading Zeros in a 16-Bit Field
Leading zeros MUST be suppressed.0開頭的字母都必須被省略，如2001:0db8::0001這是不行的，必須寫成2001:db8::1。

4.2. "::" Usage
The use of the symbol "::" MUST be used to its maximum capability. The symbol "::" MUST NOT be used to shorten just one 16-bit 0 field.
表示式必須盡可能的簡化，而且只有一個"0000"時不能簡化。所以2001:db8:0:0:0:0:2:1是不正確的，應該被寫成2001:db8::2:1。而2001:db8::1:1:1:1:1卻是不正確的，應該被寫成2001:db8:0:1:1:1:1:1。
When there is an alternative choice in the placement of a "::", the longest run of consecutive 16-bit 0 fields MUST be shortened. When the length of the consecutive 16-bit 0 fields are equal, the first sequence of zero bits MUST be shortened.
簡而言之，就是如果有兩個可以簡化::的地方，挑表示式最小，如果都是最小，則挑第一個位置。如2001:0:0:1:0:0:0:1必須被簡化為2001::1:0:0:0:1。

4.3. Lowercase
用小寫表示之。

5. Text Representation of Special Addresses

IPv4-Mapped IPv6 addresses [RFC5214]的寫法要符合前面的規則，且後面為IPv4寫法，如0:0:0:0:0:ffff:192.0.2.1應該被寫成::ffff:192.0.2.1。

6. Notes on Combining IPv6 Addresses with Port Numbers

以下是一般結合port的寫法：

• [2001:db8::1]:80
• 2001:db8::1:80
• 2001:db8::1.80
• 2001:db8::1 port 80
• 2001:db8::1p80
• 2001:db8::1#80

建議使用第一種寫法[2001:db8::1]:80。

Packet Filtering HOWTO 讀後筆記II

原文：Packet Filtering HOWTO

Packet Filtering HOWTO 讀後筆記I

7. Using iptables

Extensions to iptables: New Matches
iptables具備可擴充性(extensible)，這表示我們可以在kernel或是iptable上新增新的功能。目前kernel和iptables已經具備許多的標準擴充功能，您可以在kernel/net/netfilter目錄底下看到許多的xt_XXX.c。在iptables也會有相對應的extensions，在extensions/libxt_XXX.c，iptables的extensions會被build成shared library，需要使用-m將extensions載入。如果要取得extensions('-p'的說明，只要在後面加上-h或是--help即可。

# iptables -p tcp --help
iptables v1.4.12

Usage: iptables -[ACD] chain rule-specification [options]
       iptables -I chain [rulenum] rule-specification [options]
       iptables -R chain rulenum rule-specification [options]
       iptables -D chain rulenum [options]
       iptables -[LS] [chain [rulenum]] [options]
       iptables -[FZ] [chain] [options]
       iptables -[NX] chain
       iptables -E old-chain-name new-chain-name
       iptables -P chain target [options]
       iptables -h (print this help information)

Commands:
Either long or short options are allowed.
  --append  -A chain            Append to chain
  --check   -C chain            Check for the existence of a rule
  --delete  -D chain            Delete matching rule from chain
  --delete  -D chain rulenum
                                Delete rule rulenum (1 = first) from chain
  --insert  -I chain [rulenum]
                                Insert in chain as rulenum (default 1=first)
  --replace -R chain rulenum
                                Replace rule rulenum (1 = first) in chain
  --list    -L [chain [rulenum]]
                                List the rules in a chain or all chains
  --list-rules -S [chain [rulenum]]
                                Print the rules in a chain or all chains
  --flush   -F [chain]          Delete all rules in  chain or all chains
  --zero    -Z [chain [rulenum]]
                                Zero counters in chain or all chains
  --new     -N chain            Create a new user-defined chain
  --delete-chain
            -X [chain]          Delete a user-defined chain
  --policy  -P chain target
                                Change policy on chain to target
  --rename-chain
            -E old-chain new-chain
                                Change chain name, (moving any references)
Options:
    --ipv4      -4              Nothing (line is ignored by ip6tables-restore)
    --ipv6      -6              Error (line is ignored by iptables-restore)
[!] --proto     -p proto        protocol: by number or name, eg. `tcp'
[!] --source    -s address[/mask][...]
                                source specification
[!] --destination -d address[/mask][...]
                                destination specification
[!] --in-interface -i input name[+]
                                network interface name ([+] for wildcard)
 --jump -j target
                                target for rule (may load target extension)
  --goto      -g chain
                              jump to chain with no return
  --match       -m match
                                extended match (may load extension)
  --numeric     -n              numeric output of addresses and ports
[!] --out-interface -o output name[+]
                                network interface name ([+] for wildcard)
  --table       -t table        table to manipulate (default: `filter')
  --verbose     -v              verbose mode
  --line-numbers                print line numbers when listing
  --exact       -x              expand numbers (display exact values)
[!] --fragment  -f              match second or further fragments only
  --modprobe=          try to insert modules using this command
  --set-counters PKTS BYTES     set the counter during insert/append
[!] --version   -V              print package version.

tcp match options:
[!] --tcp-flags mask comp       match when TCP flags & mask == comp
                                (Flags: SYN ACK FIN RST URG PSH ALL NONE)
[!] --syn                       match when only SYN flag set
                                (equivalent to --tcp-flags SYN,RST,ACK,FIN SYN)
[!] --source-port port[:port]
 --sport ...
                                match source port(s)
[!] --destination-port port[:port]
 --dport ...
                                match destination port(s)
[!] --tcp-option number        match if TCP option set

Other Match Extensions
mac 這個module必須用'-m mac'或'--match mac'載入，用於比對source MAC，只能用於PREOUTING和INPUT這兩個chain。
limit 這個module必須用'-m limit'或'--match limit'載入，用於限制match的速率。--limit單位可以是/second、/minute、/hour或是/day，如5/s，每秒5個。--limit-burstnumber to match in a burst。用下圖來描述這兩者的涵義

limit-burst就是水桶的容量，limit就是水桶流出的流量，當packet裝滿水桶，後面的就會被丟棄，隨著時間過去，水桶會流出lmit個packet，就是可以再允許limit流進水桶。

7.4 Target Specifications
何謂target？what to do to the packets which match our tests. This is called a rule's target.(當match我們的條件之後，所要採取的動作就稱為rule的target)。target也可以是User-defined chains。

iptables是first match，packet進入INPUT這個chain後，會由第一條rule開始比對，如果比對成功並且有明確的target(ACCRPT/DROP)就會執行丟棄/同意packet並且終止比對，當target是另外一個chain時，就會jump到該chain中繼續進行比對，如果都沒有match，就會再回到原來的chain中繼續往下比對。

# iptables -A INPUT -p icmp
# iptables -A INPUT -p icmp -j LOG
# iptables -A INPUT -p icmp -j ACCEPT
# iptables -L -v
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination

    0     0            icmp --  any    any     anywhere             anywhere

    0     0 LOG        icmp --  any    any     anywhere             anywhere
         LOG level warning
    0     0 ACCEPT     icmp --  any    any     anywhere             anywhere


Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination


Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination

# ping 127.0.0.1 -c 1
PING 127.0.0.1 (127.0.0.1): 56 data bytes
[ 6975.682678] IN=lo OUT= MAC=00:00:00:00:00:00:00:00:00:00:00:00:08:00 SRC=127.
0.0.1 DST=127.0.0.1 LEN=84 TOS=0x00 PREC=0x00 TTL=64 ID=0 DF PROTO=ICMP TYPE=8 C
ODE=0 ID=4908 SEQ=0
[ 6975.697694] IN=lo OUT= MAC=00:00:00:00:00:00:00:00:00:00:00:00:08:00 SRC=127.
0.0.1 DST=127.0.0.1 LEN=84 TOS=0x00 PREC=0x00 TTL=64 ID=49768 PROTO=ICMP TYPE=0
CODE=0 ID=4908 SEQ=0
64 bytes from 127.0.0.1: seq=0 ttl=64 time=34.397 ms

--- 127.0.0.1 ping statistics ---
1 packets transmitted, 1 packets received, 0% packet loss
round-trip min/avg/max = 34.397/34.397/34.397 ms
# iptables -L -v
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination

    2   168            icmp --  any    any     anywhere             anywhere

    2   168 LOG        icmp --  any    any     anywhere             anywhere
         LOG level warning
    2   168 ACCEPT     icmp --  any    any     anywhere             anywhere


Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination


Chain OUTPUT (policy ACCEPT 2 packets, 168 bytes)
 pkts bytes target     prot opt in     out     source               destination

Extensions to iptables: New Targets
還有LOG、REJECT、RETURN和QUEUE等target。詳細用法請自行參考該page。

Packet Filtering HOWTO 讀後筆記I

原文：Packet Filtering HOWTO

3 What is a packet filter?

packet filter是一套軟體，會根據packet的header決定這個packet的命運，可能是ACCEPT(bypass)或是DROP，或是其他複雜的操作(NAT/QUEUE/LOG)。

3.2 How Do I Packet Filter Under Linux?
在Linux 1.1就有packet filtering功能，在1994年由Alan Cox根據BSD的ipfw移植過來，經過Jos Vos和其他人的努力，在1999年的Linux 2.4研發出第四代tool"iptables"使用至今。
iptables可以隨時的新增或刪除在kernel中的packet filtering table的rule，每當重新開機後，這些rule就會消失，您可以使用iptables-save/iptables-restore將這些rule存到檔案，或由檔案回存到kernel中。

6. How Packets Traverse The Filters

"filter"這個table有三個chain，分別是"INPUT"、"OUTPUT"和"FORWARD"。如下圖：

當packet傳入(incoming)，會先經過Routing Decision，決定封包的去向(Local In/Forwarding/Drop)，當封包經過filter的這三個chain的任何一個，都會進行rule的比對並且決定封包的去留，如果是Drop，就會立刻丟棄封包，如果是ACCEPT就會往下一個rule進行比對( `if the packet header looks like this, then here's what to do with the packet')。每一個chain都有所謂的default policy，當所有的rule在這個chain都不match，就會執行這個policy(DROP/ACCEPT)。

7. Using iptables

filter table內建的三個chain INPUT、OUTPUT和FORWARD是不能被刪除的，這裡有幾個對China進行操作的選項

1. 新增一個chain / Create a new chain (-N).
2. 刪除空白的chain / Delete an empty chain (-X).
3. 改變內建的chain的policy / Change the policy for a built-in chain. (-P).
4. 列出chain的rule / List the rules in a chain (-L).
5. 清除所有在chain中的rule / Flush the rules out of a chain (-F).
6. 清除chain中rule的counter / Zero the packet and byte counters on all rules in a chain (-Z).

以下是對rule進行操作的選項：

1. 新增rule到chain的後面 / Append a new rule to a chain (-A).
2. 插入rule到chain的某個位置 / Insert a new rule at some position in a chain (-I).
3. 取代chain中某個rule / Replace a rule at some position in a chain (-R).
4. 移除chain中某個rule / Delete a rule at some position in a chain, or the first that matches (-D).

7.2 Operations on a Single Rule
最常用到的就是append(-A)和delete(-D) rule到chain中，當然還有insert(-I)和replace(-R)。每一條rule基本上就是設定一些條件和target，當packet滿足這些條件，就會執行該target，可能是ACCEPT也可能是DROP。比如，我們要將source ip是127.0.0.1的ICMP做DROP：

# ping -c 1 127.0.0.1
PING 127.0.0.1 (127.0.0.1): 56 data bytes
64 bytes from 127.0.0.1: icmp_seq=0 ttl=64 time=0.2 ms

--- 127.0.0.1 ping statistics ---
1 packets transmitted, 1 packets received, 0% packet loss
round-trip min/avg/max = 0.2/0.2/0.2 ms
# iptables -A INPUT -s 127.0.0.1 -p icmp -j DROP
# ping -c 1 127.0.0.1
PING 127.0.0.1 (127.0.0.1): 56 data bytes

--- 127.0.0.1 ping statistics ---
1 packets transmitted, 0 packets received, 100% packet loss
#

[!] -s, --source address[/mask][,...] source address，除了可以使用IP以外，也可以是hostname，不過只有在設定的當下會做一次resolved。
[!] -p, --protocol protocol 可以是tcp、udp、udplite、icmp、esp、ah、sctp或是all，也可以是 /etc/protocols裡面的名稱，或是任何數值。
-j, --jump target This specifies the target of the rule; i.e., what to do if the packet matches it. Target也可以是 user-defined chain。
每個選項前面都可以加上!表示反向的意思。

要刪除之前設定的rule可以使用

iptables -D INPUT 1

或是

iptables -D INPUT -s 127.0.0.1 -p icmp -j DROP

第一種是刪除第一條rule，第二種是刪除符合-s 127.0.0.1 -p icmp -j DROP這個condition的rule。

常用的option還有：
[!] -i, --in-interface name packet由哪個interface收到，只能套用在INPUT、FORWARD和PREROUTING這些chain，interface name以+為結尾就表示pattern比對。如-i ppp+就會比對所有ppp開頭的interface。
[!] -o, --out-interface name packet會由哪個interface送出，只能套用在FORWARD、OUTPUT和POSTROUTING這些chain，同樣可以使用+。

6 sigma上課筆記 - Interactions Plot

人視視覺上的動物，所以由圖形上來了解趨勢會比一堆數據來的容易些，在6 sigma上課筆記 - 二維表格轉Minitab格式 中，我們想知道Temp和Press對yeild有哪什麼影響，正交互作用？逆交互作用？以及有沒有交互作用？
在Minitab中可以用Interactions Plot功能來判斷。基本判斷方法：如果圖形呈現平行，就是沒有交互作用。如果圖形呈現不對稱（有增強作用）或交叉（互逆作用），就是有交互作用。
Stat > ANOVA > Interactions Plot



由圖可知有交互作用。

6 sigma上課筆記 - 二維表格轉Minitab格式

上課的時候老師有說到，我們常常拿到的表格是二維的，最好把他轉成統計上常用的格式Stack Rows(switch rows to columns)，為什麼要這種格式呢？因為這樣如果增加實驗因子，整個表格不會有太大變動。
假設實驗數據如下：



我們可以在Minitab 14中執行Data > Stack > Rows


因為Press 1/Press 2這兩column的資料是要堆疊的，所以放置在to be stacked。
Store stacked data in是堆疊後的資料，我們放在下一個空白的 column，並且命名為yield。
Store column subscripts in是column這個factor，我們是Press 1/Press 2，所以我們命名為Press。
Expand the following columns while stacking rows就是row這個factor，我們是Temp 1/Temp 2，所以我們命名為Temp。


最後就是跑出來的worksheet了

An Introduction To The SQLite C/C++ Interface

為了能夠用SQL將資料由資料庫撈出，我們必須認識兩個主要的Object：

1. The database connection object：sqlite3
執行sqlite3_open()之後，就會得到該object，感覺類似open之後的file descriptor。

2. The prepared statement object：sqlite3_stmt
把SQL轉成bytecode，但是還沒真正被執行。請參考Compiling An SQL Statement/To execute an SQL query, it must first be compiled into a byte-code program using one of these routines.
An instance of this object represents a single SQL statement. This object is variously known as a "prepared statement" or a "compiled SQL statement" or simply as a "statement".

一個常見的SQLite pattern為：

1. sqlite3_open()：取得database connection object。
2. sqlite3_preapre() ：取得prepared statement object。
3. sqlite3_step()：執行prepared statement object。
4. sqlite3_column_<type>()：將sqlite回傳回來的資料，轉成對應的type取出。
5. sqlite3_finalize()：釋放prepared statement object。
6. sqlite3_close()：釋放database connection object。

#include <iostream>
#include <sqlite3.h>
#include <cstdlib>
#include <assert.h>

using namespace std;

int main(int argc, char** argv)
{
  sqlite3 *conn;
  sqlite3_stmt *statement; // SQL Statement Object
  int ret = 0;
  int cols;

  // This routine opens a connection to an SQLite database file
  //  and returns a database connection object.
  ret = sqlite3_open_v2("hello.db", &conn, SQLITE_OPEN_READONLY, NULL);
  if (ret) {
    cout << "can not open database\n";
    exit(0);
  }

  ret = sqlite3_prepare_v2(conn, "select * from hello", -1, &statement, NULL);
  if (ret != SQLITE_OK) {
    cout << "We did not get any data\n";
    exit(0);
  }

  cols = sqlite3_column_count(statement);

  for (int col = 0; col < cols; col++) {
    cout << " " << sqlite3_column_name(statement, col);
  };
  cout << endl;

  while (true) {
    ret = sqlite3_step(statement);
    if (ret == SQLITE_ROW) {
      for (int col = 0; col < cols; col++) {
        switch (sqlite3_column_type(statement, col)) {
          case SQLITE_INTEGER:
            cout << " " << sqlite3_column_int(statement, col) << " ";
            break;
          case SQLITE_FLOAT:
            cout << " " << sqlite3_column_double(statement, col) << " ";
            break;
          case SQLITE_TEXT:
            cout << " " << sqlite3_column_text(statement, col) << " ";
            break;
          case SQLITE_NULL:
            cout << " " << "NULL" << " ";
            break;
        }
      };
      cout << endl;
    } else if (ret == SQLITE_DONE) {
      cout << "done" << endl;
      break;
    } else {
      cout << "ret:" << ret << endl;
      break;
    }
  }

  sqlite3_finalize(statement);
  sqlite3_close(conn);

  return 0;
}

sqlite3_exec()是將sqlite3_prepare_v2(), sqlite3_step()和 sqlite3_finalize()包裝起來的API，其原型為

int sqlite3_exec(
  sqlite3*,                                  /* An open database */
  const char *sql,                           /* SQL to be evaluated */
  int (*callback)(void*,int,char**,char**),  /* Callback function */
  void *,                                    /* 1st argument to callback */
  char **errmsg                              /* Error msg written here */
);

• 第二個參數要執行的SQL statement。
• 第三個參數是callback function。每一個row都會呼叫該callback一次。
• 第四個參數是要傳給callback function的data。
• 第五個參數就是發生錯誤時，儲存錯誤資訊的指標。

因此上面的程式可以改寫為

#include <iostream>
#include <sqlite3.h>

using namespace std;

int callback(void *data, int column, char **value, char **name)
{
  int i;
  cout << (char *)data << endl;
  for (i = 0; i < column; i++) {
    cout << name[i] << ":" << (value[i] ?: "NULL") << endl << flush;
  }
  return 0;
}


int main(int argc, char** argv)
{
  sqlite3 *conn;
  int ret = 0;
  char *errmsg = NULL;
  char data[] = "brook";

  // This routine opens a connection to an SQLite database file
  //  and returns a database connection object.
  ret = sqlite3_open_v2("hello.db", &conn, SQLITE_OPEN_READONLY, NULL);
  if (ret != SQLITE_OK) {
     cout << sqlite3_errmsg(conn) << ".(" << ret << ")" << endl;
     exit(0);
  }

  ret = sqlite3_exec(conn, "select * from hello", callback, data, &errmsg);
  if (ret != SQLITE_OK) {
     cout << "We did not get any data. " << errmsg << endl;
     sqlite3_free(errmsg);
  }

  sqlite3_close(conn);

  return 0;
}

參考資料：
• An Introduction To The SQLite C/C++ Interface
• One-Step Query Execution Interface

Introduction SQLite

大家比較耳熟能詳的database大多是client/server的架構居多，如：MySQL、PostgreSQL、MS-SQL和Oracle等等，而SQLite感覺比較像MS的Access， 程式本身就負責開啟資料庫並且直接操作，更多的資訊可以參考官網http://www.sqlite.org/。

以下就個人在SQLite網站看到的介紹，寫下一些筆記。
About SQLite
SQLite不像許多SQL資料庫有分開的Server process。SQLite直接對資料庫檔案做存取，這些資料庫檔案室可以跨平台的， 意味著您可以直接在32/64和big-endian/little-endian複製這些資料庫檔案，都能正確地被SQLite所存取。

Appropriate Uses For SQLite/Situations Where Another RDBMS May Work Better SQLite因為直接對database做存取，所以多個client同時對某database做存取可能會有問題。 如果是高流量(High-volume Websites)或是高資料量(Very large datasets)都不適合SQLite，畢竟它是拿來給embedded用的。

總體而言，對於小資料庫的應用SQLite已經是非常好的選擇了。


基本操作

brook:~$ ls hello.db
ls: cannot access hello.db: No such file or directory
brook:~$ sqlite hello.db
Loading resources from /home/brook/.sqliterc
SQLite version 2.8.17
Enter ".help" for instructions
sqlite> .help
.databases             List names and files of attached databases
.dump ?TABLE? ...      Dump the database in a text format
.echo ON|OFF           Turn command echo on or off
.exit                  Exit this program
.explain ON|OFF        Turn output mode suitable for EXPLAIN on or off.
.header(s) ON|OFF      Turn display of headers on or off
.help                  Show this message
.indices TABLE         Show names of all indices on TABLE
.mode MODE             Set mode to one of "line(s)", "column(s)",
                       "insert", "list", or "html"
.mode insert TABLE     Generate SQL insert statements for TABLE
.nullvalue STRING      Print STRING instead of nothing for NULL data
.output FILENAME       Send output to FILENAME
.output stdout         Send output to the screen
.prompt MAIN CONTINUE  Replace the standard prompts
.quit                  Exit this program
.read FILENAME         Execute SQL in FILENAME
.schema ?TABLE?        Show the CREATE statements
.separator STRING      Change separator string for "list" mode
.show                  Show the current values for various settings
.tables ?PATTERN?      List names of tables matching a pattern
.timeout MS            Try opening locked tables for MS milliseconds
.width NUM NUM ...     Set column widths for "column" mode

sqlite> .tables
sqlite> create table hello (x integer PRIMARY KEY ASC, y);
sqlite> .tables
hello
sqlite> insert into hello (y) values('a');
sqlite> insert into hello (y) values(10);
sqlite> insert into hello (y) values(datetime('now'));
sqlite> select * from hello;
x           y
----------  ----------
1           a
2           10
3           2012-07-30
sqlite> .quit

我們也可以直接在command line上面執行sqlite

brook:~$ sqlite hello.db .dump
Loading resources from /home/brook/.sqliterc
BEGIN TRANSACTION;
create table hello (x integer PRIMARY KEY ASC, y);
INSERT INTO hello VALUES(1,'a');
INSERT INTO hello VALUES(2,10);
INSERT INTO hello VALUES(3,'2012-07-30 04:20:12');
COMMIT;
brook:~$ sqlite hello.db "select * from hello"
Loading resources from /home/brook/.sqliterc
x           y
----------  ----------
1           a
2           10
3           2012-07-30
brook:~$ cat ~/.sqliterc
.mode column
.header on
.nullvalue NULL

更多SQL語法請參考http://www.sqlite.org/lang.html

參考資料：
• http://www.sqlite.org/

Pipe to a Subprocess

偶爾想偷懶的我會在code中使用system()，呼叫shell來執行一些東西，並且將執行完的結果丟回來程式中處理，這時候popen就很好用了，popen - pipe stream to or from a process。
popen允許開啟read或write pipe，不能夠同時開啟為read/write，read可以讓程式從popen中讀回來處理，而write可以將程式中的資料丟到popen處理。

popen(,"r")

#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
    char buf[128];
    float a, b, c, d;
    FILE *fp;
    if ((fp = popen("(df -h 2>/dev/null) | tail -n +2", "r")) == NULL) {
        fprintf(stderr, "popen() failed\n");
        return -1;
    }
    while (!feof(fp)) {
        fscanf(fp, "%*[^ ]%f%*[^1-9]%f%*[^1-9]%f%*[^1-9]%f%%%*[^\n]", &a, &b, &c, &d);
        printf("%f/%f/%f/%f\n", a, b, c, d);
    }
    return 0;
}

popen(,"w")

#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
    char buf[] = "1 2 3 4 5";
    float a, b, c, d;
    FILE *fp;
    if ((fp = popen("xargs -n 1 > /tmp/xx", "w")) == NULL) {
        fprintf(stderr, "popen() failed\n");
        return -1;
    }
    fprintf(fp, "%s", buf);
    pclose(fp);
    return 0;
}

參考資料：
• The GNU C Library, Chapter 15.2

Design Patterns - Command pattern

Command pattern是一種將Action封裝起來，並提供一個general的interface作為呼叫時(invoke)的統一介面。

舉個生活例子來說明，想必您一定用過萬用遙控器，User可以設定遙控器上某個按鈕1的功能為電視的開關，所以當User按下按鈕1，就可以開關電視，接著User設定按鈕2為控制冷氣的開關，所以當User按下按鈕2，就可以開關冷氣，這樣簡單的運作就是一種Command Pattern。
電視開關是一種Action，被封裝成遙控器上面的按鈕，對User來說，這是一個General的interface，而且User在變更任和按鈕功能時，並不會影響遙控器上面的其他按鈕。

Command pattern有三個名詞需要解釋一下：
client：The client instantiates the command object and provides the information required to call the method at a later time.
invoker: The invoker decides when the method should be called.
receiver: The receiver is an instance of the class that contains the method's code.

client就可以想成"設定按鈕"的動作，invoker就是User了，而receiver就是電器了。

圖取自http://en.wikipedia.org/wiki/Command_pattern.

#include <iostream>

class Command {
public:
    virtual int exec(void *args) = 0;
};

// Receiver
class TV {
    bool turn_on_off;
public:
    void pwr_switch() {
        if (turn_on_off) {
            std::cout << "Turn off TV" << std::endl;
        } else {
            std::cout << "Turn on TV" << std::endl;
        }
        turn_on_off = !(turn_on_off);
    }
};

class CmdTvSwitch: public Command {
    TV *_tv;
public:
    CmdTvSwitch(TV *tv) {
        this->_tv = tv;
    }
    virtual int exec(void *args) {
        this->_tv->pwr_switch();
        return 0;
    }
};

int main(int argc, char *argv[])
{
    // Client
    TV tv;
    Command  *c;
    c = new CmdTvSwitch(&tv);
    c->exec(NULL);
    c->exec(NULL);
    return 0; 
}

就目前個人在使用這個Pattern上面的感觸就是"Command pattern是一種將Action封裝起來，並提供一個general的interface作為呼叫時(invoke)的統一介面。"比如，我在寫Message Queue會用到，提供新的指令供外界呼叫也會用到。

參考資料：

1. http://en.wikipedia.org/wiki/Command_pattern
2. http://caterpillar.onlyfun.net/Gossip/DesignPattern/CommandPattern.htm

理財常用的Link

股匯市原物料期貨報價, http://www.stockq.org/
全球股市排行榜, http://www.stockq.org/market/
貨幣各國匯率歷史紀錄, http://fxtop.com/en/historates.php
金磚四國和台灣股市走勢圖, http://finance.yahoo.com
台灣地區銀行利率, http://www.taiwanrate.com/
台灣地區各網路銀行入口, http://www.easyatm.com.tw/playatm.html
文茜世界財經週報, http://www.youtube.com
57金錢爆, http://www.youtube.com
國際主要股市月報 , http://www.twse.com.tw/ch/statistics/statistics.php
基金績效,
台股上市公司本益比, http://www.twse.com.tw
台股上櫃公司本益比, http://www.otc.org.tw
基金定期定額試算, http://fund.scsb.com.tw
STOCK-AI提供各類經濟指標數據, https://stock-ai.com/
blog
法意聯盟, http://www.wretch.cc/blog/joejoejoe



持續更新中...

常用的regular expression

這篇會慢慢增加內容，所以我也會更新發布日期。
JavaScript

    var mac = /^\s*([\d[a-f]{2}:){5}[\d[a-f]{2}\s*$/i;
    var ip = /^((\d)|(([1-9])\d)|(1\d\d)|(2(([0-4]\d)|5([0-5]))))\.((\d)|(([1-9])\d)|(1\d\d)|(2(([0-4]\d)|5([0-5]))))\.((\d)|(([1-9])\d)|(1\d\d)|(2(([0-4]\d)|5([0-5]))))\.((\d)|(([1-9])\d)|(1\d\d)|(2(([0-4]\d)|5([0-5]))))$/;

C language

    char *mac =  "([[0-9a-fA-F]{2}:){5}[0-9a-fA-F]{2}";
    char *ip = "^(([0-9])|(([1-9])[0-9])|(1[0-9][0-9])|(2(([0-4][0-9])|5([0-5]))))\\.(([0-9])|(([1-9])[0-9])|(1[0-9][0-9])|(2(([0-4][0-9])|5([0-5]))))\\.(([0-9])|(([1-9])[0-9])|(1[0-9][0-9])|(2(([0-4][0-9])|5([0-5]))))\\.(([0-9])|(([1-9])[0-9])|(1[0-9][0-9])|(2(([0-4][0-9])|5([0-5]))))$";

參考資料
1. http://en.wikipedia.org/wiki/Regular_expression

頁面遮罩

我們常常可以在Web上看到，當有事件在背景執行時，Web會跳出半透明的視窗遮住後面的頁面，如：


這裡主要是利用JavaScript控制layer(Z-Index)，以及style的opacity和style的display達成，layer控制element之間的stack，也就是MS office裡面常常提到的，"往上/下一層"，style.opacity則是透明度，style.display控制顯示或隱藏，這些就可以達成頁面遮罩的功能了。

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head>
  <script type="text/javascript">
//<![CDATA[
    function show() {
      document.getElementById("xie").style.display = "";
      document.getElementById("content1").style.display = "";
      document.getElementById("content1").innerHTML = "內容<br/><input onclick='hide()' type='button' value='確定'/>";
    }

    function hide() {
      document.getElementById("xie").style.display = "none";
      document.getElementById("content1").style.display = "none";
    }
  //]]>
  </script>
  <title>JavaScript Mask</title>
</head>

<body>
  <div style=
  "filter:alpha(opacity=50); -moz-opacity:0.5; opacity: 0.5; width: 100%; background-color: White; display: none; height: 100%; position: absolute; left: 0; top: 0;"
       id="xie"></div>

  <div style=
  "width: 100px; background-color: Red; display: none; height: 53px; position: absolute; left: 144px; top: 100px;"
       id="content1"></div>

  <input onclick="show()" type="button" value="顯示" />
</body>
</html>

參考資料：
• CSS z-index Property
• STYLE= filter Alpha（已解決）

動態產生HTML element -- document.createElement

我們可以利用document.createElement()動態的產生HTML的element，再利用Node.appendChild()插入某個Node底下，或利用Node.removeChild()自某個Node底下移除，更多資訊可以參考[1]。

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
  <title>auto table</title>
</head>

<body>
  <table id="brook" summary=""></table>
  <script type="text/javascript">
  //<![CDATA[
    function create_new_row_button(eT, msg) {
        var eR = document.createElement("tr");
        var eC = document.createElement("td");
        var eB = document.createElement("input");
        eB.type = "button"
        eB.value= msg;
        eB.style.width = "100px";

        eT.appendChild(eR);
        eR.appendChild(eC);
        eC.appendChild(eB);
    }
    var station = [
        {name: "CHT"},
        {name: "TW"},
    ];
    for (var i = 0; i < station.length; i++) {
        create_new_row_button(document.getElementById("brook"),
                              station[i].name);
    }
  //]]>
  </script>
</body>
</html>

參考文件：
• Document Object Model (DOM) Level 1 Specification Version 1.0, Chapter 1: Document Object Model (Core) Level 1

glibc讀書心得 -- Ch2 Error Reporting

在glibc中會去偵錯並且回傳錯誤值，通常我們都應該去檢查這些回傳值，並且作error-handling，比如開檔 open()/fopen()，並非每次都會開成功，所以，open()/fopen()通常都會去檢查return value是不是有正確。

2.1 Checking for Errors
glibc的return value通常是-1、NULL或是EOF，這只能知道錯誤發生，至於發生何種錯誤，都是存在errno這個變數中，當您要使用errno必須include <errno.h>。這個header file也定義很多error code，都是以E為開頭，這些error code在Ch 2.2中有說明，用到再查就OK啦。

2.2 Error Codes
這個章節主要說明定義的error code，值得注意的是EAGAIN和EWOULDBLOCK的值一樣，所以不能放在同一個case switch中，其實我常用的error code大概只有他列的1/5不到吧，看看就好。

2.3 Error Messages 基本上我們都是希望report的錯誤是文字型態，而不是只有error code，所以glibc有提供一些轉換的function：

char * strerror(int errnum)	[Function]
char * strerror_r(int errnum, char *buf, size t n)	[Function]
void perror(const char *message)	[Function]
char * program_invocation_name	[Variable]
char * program_invocation_short_name	[Variable]
void error (int status, int errnum, const char *format, . . . )	[Function]
error_at_line (int status, int errnum, const char *fname,unsigned int lineno, const char *format, . . . )	[Function]

char * strerror(int errnum)
將errnum轉成相對應的字串

#include <stdio.h>
#include <errno.h>  // EINTR
#include <string.h> // strerror()

int main(int argc, char *argv[])
{
    printf("%s\n", strerror(EINTR));
    // print out "Interrupted system call"
    return 0;
}

char * strerror_r(int errnum, char *buf, size t n)
strerror的reentrant版本，mutli-thread就一定要用這個版本。

#define _GNU_SOURCE
#include <stdio.h>
#include <errno.h>  // EINTR
#include <string.h> // strerror()

int main(int argc, char *argv[])
{
    char buf[32];
    printf("%s\n", strerror_r(EINTR, buf, sizeof(buf)));
    // print out "Interrupted system call"
    return 0;
}

void perror(const char *message)
效果和printf(stderr, "%s:%s", message, strerror(errno))相似，把error message寫到stderr去，接著冒號後面再接errno的message。

#include <stdio.h>
#include <errno.h>  // EINTR
#include <string.h> // strerror()

int main(int argc, char *argv[])
{
    perror("my_perror_msg1");
    // print out "my_perror_msg1: Success"
    errno = EINTR;
    perror("my_perror_msg2");
    // print out "my_perror_msg2: Interrupted system call"
    return 0;
}

char * program_invocation_name / char * program_invocation_short_name
該程式的名稱，和argv[0]的值一樣。

#include <stdio.h>
#include <errno.h>  // EINTR
#include <string.h> // strerror()

int main(int argc, char *argv[])
{
    printf("%s\n", argv[0]);
    // print out "./a.out"
    printf("%s\n", program_invocation_name);
    // print out "./a.out"
    printf("%s\n", program_invocation_short_name);
    // print out "a.out"
    return 0;
}

void error (int status, int errnum, const char *format, . . . )
status不為0時，就等同exit(status)，後面的參數errnum和format用途類似perror()，當errnum為0時，就不會印後面的message，但是perror()會印Success。

#include <stdio.h>
#include <errno.h>  // EINTR
#include <string.h> // strerror()

int main(int argc, char *argv[])
{
    error(0, 0, "%s", "msg");
    error(0, EINTR, "%s", "msg");
    // print out "./a.out: msg: Interrupted system call"
    error(1, EINTR, "%s", "msg");
    // print out "./a.out: msg: Interrupted system call" and exit(1)
    return 0;
}

error_at_line(int status, int errnum, const char *fname, unsigned int lineno, const char *format, ...)
error_at_line()和error()很像，只是多了fname和lineno印出檔案名稱和行號。

#include <stdio.h>
#include <errno.h>  // EINTR
#include <string.h> // strerror()

int main(int argc, char *argv[])
{
    error_at_line(0, 0, __FILE__, __LINE__, "%s", "msg");
    // print out "./a.out:error_at_line.c:7: msg"
    error_at_line(0, EINTR, __FILE__, __LINE__, "%s", "msg");
    // print out "./a.out:error_at_line.c:8: msg: Interrupted system call"
    error_at_line(1, EINTR, __FILE__, __LINE__, "%s", "msg");
    // print out "./a.out:error_at_line.c:11: msg: Interrupted system call"
    return 0;
}

參考資料：
• The GNU C Library, Chapter 2

IE8無法下載檔案

話說有一天，我用Luci寫一段download動態產生的檔案時，發生部分的IE8下載有問題，都會產生無法下載的訊息，當然就是立刻請問google大神，尋得此文章[PHP]下載檔案時無法直接開啟文件的解法方法，雖然是用PHP寫，不過小改一下就可以在Luci上面如法炮製啦。

[PHP]下載檔案時無法直接開啟文件的解法方法

header("Content-Type: application/octetstream; name=$FILEname"); //for IE & Opera
header("Content-Type: application/octet-stream; name=$FILEname"); //for the rest
header("Content-Disposition: attachment; filename=$FILEname;");
header("Content-Transfer-Encoding: binary");
header("Cache-Control: cache, must-revalidate");
header("Pragma: public");
header("Expires: 0");

Luci不過就是改呼叫luci.http.header()。
[Luci]下載檔案時無法直接開啟文件的解法方法

luci.http.header("Content-Type", "application/octetstream; name=" .. fname); //for IE & Opera
luci.http.header("Content-Type", "application/octet-stream; name=" .. fname); //for the rest
luci.http.header("Content-Disposition", "attachment; filename=" .. fname);
luci.http.header("Content-Transfer-Encoding", "binary");
luci.http.header("Cache-Control", "cache, must-revalidate");
luci.http.header("Pragma", "public");
luci.http.header("Expires", "0");

參考資料
• [PHP]下載檔案時無法直接開啟文件的解法方法
• http://luci.subsignal.org/api/luci/modules/luci.http.html#header

glibc讀書心得 -- Ch1 Introduction

1.1 Getting Started
C語言並沒有內建一些常用的操作，如input/output、memory management等等，這些通通被定義在Standard Library中(glibc)。

1.2 Standards and Portability
glibc參考的C Library標準有ISO C(American National Standard X3.159-1989—“ANSI C” and later by the International Standardization Organization (ISO): ISO/IEC 9899:1990, “Programming languages—C”.)和POSIX兩個。以及參考System V和Berkeley UNIX兩個實做而成。

1.3 Using the Library
Library在C主要由兩個部份組成：

1. header files that define types and macros and declare variables and functions
2. the actual library or archive that contains the definitions of the variables and functions.

為了能使用glibc，你必須將所需的header file，用＃include這個preprocessor directive將其引入，嚴格來說，您可以不必include這些header file，只要您可以正確的宣告相關的變數、巨集等等，不過為了效率和能正確的宣告相關變數，我們都會採用header file的形式，將其引入(include)。至於Macro的部份就參考我之前的C preprocessor的文章GCC - C Preprocessor應該會更清楚。
關於Reserved Names個人覺得還蠻重要的，就直接貼出來了：

1. Names beginning with a capital ‘E’ followed a digit or uppercase letter may be used for additional error code names. See Chapter 2 [Error Reporting], page 13.
2. Names that begin with either ‘is’ or ‘to’ followed by a lowercase letter may be used for additional character testing and conversion functions. See Chapter 4 [Character Handling], page 65.
3. Names that begin with ‘LC_’ followed by an uppercase letter may be used for additional macros specifying locale attributes. See Chapter 7 [Locales and Internationalization], page 150.
4. Names of all existing mathematics functions (see Chapter 19 [Mathematics], page 466) suffixed with ‘f’ or ‘l’ are reserved for corresponding functions that operate on float and long double arguments, respectively.
5. Names that begin with ‘SIG’ followed by an uppercase letter are reserved for additional signal names. See Section 24.2 [Standard Signals], page 592.
6. Names that begin with ‘SIG_’ followed by an uppercase letter are reserved for additional signal actions. See Section 24.3.1 [Basic Signal Handling], page 600.
7. Names beginning with ‘str’, ‘mem’, or ‘wcs’ followed by a lowercase letter are reserved for additional string and array functions. See Chapter 5 [String and Array Utilities], page 73.
8. Names that end with ‘_t’ are reserved for additional type names.

參考資料：
1. The GNU C Library, Chapter 1

JSON-C

JSON-C是一套用C寫的JSON format的parser和generator，可以將JSON字串正確parse，並且存成json_object進行操作(新增/刪除/修改)，也可以將json_object轉成JSON字串，個人還蠻推薦的。

官方網站：JSON-C

安裝步驟

brook@vista:~/src$ git clone https://github.com/json-c/json-c.git json-c
Cloning into json-c...
remote: Counting objects: 448, done.
remote: Compressing objects: 100% (169/169), done.
remote: Total 448 (delta 315), reused 405 (delta 274)
Receiving objects: 100% (448/448), 125.68 KiB | 76 KiB/s, done.
Resolving deltas: 100% (315/315), done.
brook@vista:~/src$ cd json-c/
brook@vista:~/src/json-c$ ./autogen.sh
autoreconf: Entering directory `.'
autoreconf: configure.in: not using Gettext
autoreconf: running: aclocal 
autoreconf: configure.in: tracing
autoreconf: running: libtoolize --install --copy
libtoolize: Consider adding `AC_CONFIG_MACRO_DIR([m4])' to configure.in and
libtoolize: rerunning libtoolize, to keep the correct libtool macros in-tree.
libtoolize: Consider adding `-I m4' to ACLOCAL_AMFLAGS in Makefile.am.
autoreconf: running: /usr/bin/autoconf
autoreconf: running: /usr/bin/autoheader
autoreconf: running: automake --add-missing --copy --no-force
autoreconf: Leaving directory `.'
brook@vista:~/src/json-c$ ./configure
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for a thread-safe mkdir -p... /bin/mkdir -p
...
brook@vista:~/src/json-c$ make
make  all-am
make[1]: Entering directory `/home/brook/src/json-c'
/bin/bash ./libtool --tag=CC   --mode=compile gcc -DHAVE_CONFIG_H -I.    -Wall -Wwrite-strings -Werror -std=gnu99 -D_GNU_SOURCE -D_REENTRANT -g -O2 -MT arraylist.lo -MD -MP -MF .deps/arraylist.Tpo -c -o arraylist.lo arraylist.c
...
brook@vista:~/src/json-c$ make check
make  test1 test2 test4 test_parse_int64 test_null test_cast
make[1]: Entering directory `/home/brook/src/json-c'
gcc -DHAVE_CONFIG_H -I.    -Wall -Wwrite-strings -Werror -std=gnu99 -D_GNU_SOURCE -D_REENTRANT -g -O2 -MT test1.o -MD -MP -MF .deps/test1.Tpo -c -o test1.o test1.c
test1.c: In function ‘sort_fn’:
test1.c:14:8: error: assignment discards ‘const’ qualifier from pointer target type [-Werror]
test1.c:15:8: error: assignment discards ‘const’ qualifier from pointer target type [-Werror]
cc1: all warnings being treated as errors

make[1]: *** [test1.o] Error 1
make[1]: Leaving directory `/home/brook/src/json-c'
make: *** [check-am] Error 2
brook@vista:~/src/json-c$ sed -i 's/-Werror //' Makefile
brook@vista:~/src/json-c$ make check
make  test1 test2 test4 test_parse_int64 test_null test_cast
make[1]: Entering directory `/home/brook/src/json-c'
...
brook@vista:~/src/json-c$ ./test1
my_string= 
my_string.to_string()="\t"
my_string=\
my_string.to_string()="\\"
my_string=foo
my_string.to_string()="foo"
my_int=9
my_int.to_string()=9
my_array=
 [0]=1
 [1]=2
 [2]=3
 [3]=null
 [4]=5
...

Parser
可以利用json_tokener_parse()直接將字串轉成json_object，或是利用json_object_from_file()直接將檔案轉成json_object。

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

#include "json.h"


int main(int argc, char **argv)
{
  json_object *new_obj;

  MC_SET_DEBUG(1);

  new_obj = json_tokener_parse("/* more difficult test case */ { \"glossary\": { \"title\": \"example glossary\", \"GlossDiv\": { \"title\": \"S\", \"GlossList\": [ { \"ID\": \"SGML\", \"SortAs\": \"SGML\", \"GlossTerm\": \"Standard Generalized Markup Language\", \"Acronym\": \"SGML\", \"Abbrev\": \"ISO 8879:1986\", \"GlossDef\": \"A meta-markup language, used to create markup languages such as DocBook.\", \"GlossSeeAlso\": [\"GML\", \"XML\", \"markup\"] } ] } } }");
  printf("new_obj.to_string()=%s\n", json_object_to_json_string(new_obj));
  json_object_put(new_obj);

  return 0;
}

Generator基本上就是用json_object_to_json_string()將json_object轉成字串。

更多的範例可以參考source code裡面的test1.c。

Turn your Linux computer into a wireless access point using hostapd

話說手持無線裝置越來越多，習慣晚上用我的android手機上網，不過有天竟然把AP帶回老家忘記帶回來，只好拿我的HP Compaq CQ45來充當AP了，網路上已經很多Turn your Linux computer into a wireless access point using hostapd這類的文章了，我就不多加闡述，只是單純的紀錄。
我的CQ45的網卡是Broadcom的Chip，用的Linux kernel是3.0.0，預設的wireless driver是去load wl.ko，產生的interface name是eth1，不過hostap好像不支援，也沒去深究他，索性把他換成舊的b43.ko，然後簡單設定一下hostapd.conf就執行hostapd了。

hostapd.conf

ssid=test
hw_mode=g
channel=1
interface=wlan1
#bridge=br1
driver=nl80211
ignore_broadcast_ssid=0
macaddr_acl=0
wmm_enabled=0

接著還要設定wireless的IP，不過我並沒有啟動DHCP server，Client端就用靜態IP吧。

接著還要讓我的NB具有route和NAT的功能，請執行
sudo iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
sudo sysctl -w sys.net.ipv4.conf.all.forwarding=1

send signal to user-space

某天有個需求是希望當kernel發生某事件時通知user-space的process，心裡想最快就是送signal，於是google一下，果然有人有類似的需求，signals handling in the kernel，於是改了一下把他放上來，值得一提的是，其實這樣並不被鼓勵的，而且原本的kill_proc_info並沒有被export出來，所以如果是module要使用的話，就必須把他export出來，EXPORT_SYMBOL(kill_proc_info)。

#include <linux/module.h>
#include <linux/init.h>
#include <linux/moduleparam.h>

#include <linux/sched.h>
#include <linux/kernel.h> /* printk() */
// #include <linux/slab.h> /* kmalloc() */
#include <linux/errno.h>  /* error codes */
#include <linux/types.h>  /* size_t */
#include <linux/signal.h>
#include <linux/proc_fs.h>
#include <linux/uaccess.h>

#define PROC_NAME "sig2pid"

/**
 * 送signal 到pid去
 */
static int send_sig_to_pid(int sig, pid_t pid)
{
    struct siginfo info;

    info.si_signo = sig;
    info.si_errno = 0;
    info.si_code = SI_USER; // sent by kill, sigsend, raise
    info.si_pid = get_current()->pid; // sender's pid
    info.si_uid = current_uid(); // sender's uid

    return kill_proc_info(sig, &info, pid);
}

/**
 * /proc/sig2pid的write ops
 */
static int
sig2pid_proc_write(struct file *file, const char __user * buffer,
                     unsigned long count, void *data)
{
    int sig, pid, ret;
    char line[count];
    ret = copy_from_user(line, buffer, count);

    if (ret) {
        return -EFAULT;
    }
    sscanf(line, "%d %d", &pid, &sig);
    printk("%s(#%d): pid(%d), sig(%d)\n",
            __func__, __LINE__, pid, sig);
    send_sig_to_pid(sig, (pid_t) pid);
    return count;
}

/**
 * 建立/proc/sig2pid
 */
static int create_proc_file(void)
{
    struct proc_dir_entry *p;
    p = create_proc_entry(PROC_NAME, S_IFREG | S_IWUGO, NULL);
    if (!p) {
        printk("%s(#%d): create proc entry failed\n", __func__, __LINE__);
        return -EFAULT;
    }
    p->write_proc = sig2pid_proc_write;
    return 0;
}

int sig2pid_init_module(void)
{
    return create_proc_file();
}

void sig2pid_exit_module(void)
{
    remove_proc_entry(PROC_NAME, NULL);
}

module_init(sig2pid_init_module);
module_exit(sig2pid_exit_module);

參考資料：
• http://old.nabble.com/signals-handling-in-the-kernel-to12032525.html#a12032525 , signals handling in the kernel.
• http://kerneltrap.org/node/5800, how to send signal from kernel space to user space.

github： https://github.com/brook-kuo/Linux_Module/tree/master/process/send_sig_to_userspace

Allow Unix sockets to be treated like normal files.

某天忽然想要用echo/cat的方式直接對unix socket做存取，結果得到error，只好有請google大神，覓得此良方Allow Unix sockets to be treated like normal files，try了一下沒問題。

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <stdlib.h>

#define handle_error(msg) \
        do { perror(msg); exit(EXIT_FAILURE); } while (0)

int main(int argc, char *argv[])
{
    int srv_fd, cli_fd;
    socklen_t cli_len;
    struct sockaddr_un srv_addr, cli_addr;
    char buf[128] = "Brook: ";
    ssize_t len;

    unlink("server_socket");
    if ((srv_fd = socket(AF_UNIX, SOCK_STREAM, 0)) < 0) {
        handle_error("socket");
    }

    srv_addr.sun_family = AF_UNIX;
    strcpy(srv_addr.sun_path, "/tmp/unix_sock");
    if (bind(srv_fd, (struct sockaddr *)&srv_addr, sizeof(srv_addr)) < 0) {
        handle_error("bind");
    }

    if (listen(srv_fd, 1) < 0) {
         handle_error("listen");
    }

    while (1) {
        cli_fd = accept(srv_fd, (struct sockaddr *)&cli_addr, &cli_len);
        len = read(cli_fd, buf + 6, sizeof(buf) - 6);
        buf[6 + len] = 0;
        write(cli_fd, buf, strlen(buf));
        close(cli_fd);
    }
    return 0;
}

參考資料：
• http://lwn.net/Articles/415651/ , net/unix: Allow Unix sockets to be treated like normal files.

github：
https://github.com/brook-kuo/Linux_Module/tree/master/socket/unix_as_normal_file

socket programming in bash

關於Bash的Socket部份您可以在man page中看到這段描述：

/dev/tcp/host/port
        If host is a valid hostname or Internet address, and port is an integer
        port number or service name, bash attempts to open a TCP connection to
        the corresponding socket.

/dev/udp/host/port
        If host is a valid hostname or Internet address, and port is an integer
        port number or service name, bash attempts to open a UDP connection to 
        the corresponding socket.

用一個簡單的例子就會懂了

HTML5 canvas的初體驗

HTML5的新的element，canvas，可以在Browser上繪製圖表/圖片。使用時必須訂出繪製的範圍(width/height)，接著就可以開始用JavaScript進行繪圖了。目前多數支援canvas的browser看來也都只有支援2D，未來應該會有3D的。

<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
        <title>Canvas/Simple shapes (rectangles)</title>
    </head>
<body>
    <canvas id="myCanvas" width="300" height="150">
    Fallback content, in case the browser does not support Canvas.
    </canvas>
    <script type="application/x-javascript">
        // Get a reference to the element.
        var elem = document.getElementById('myCanvas');

        // 判斷是否能取得context
        if (elem && elem.getContext) {
            // 你只能對每一個canvas做initialize一次(getContext).
            // context = canvas . getContext(contextId [, ... ])
            var context = elem.getContext('2d');
            if (context) {
                // context.fillRect(x, y, w, h)
                // 畫方形
                context.fillRect(0, 0, 150, 100);

                // context.clearRect(x, y, w, h)
                // 清方形
                context.clearRect(100,50, 50, 50);

                // context.strokeRect(x, y, w, h)
                // 畫框
                context.strokeRect(150,100, 50, 50);
            }
        }
    </script>
</body>
</html>

fillRect(x, y, w, h)使用fillStyle來決定顏色。

<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
        <title>Canvas/FillRect attribute</title>
    </head>
<body>
    <canvas id="myCanvas" width="300" height="150">
    Fallback content, in case the browser does not support Canvas.
    </canvas>
    <script type="application/x-javascript">
        // Get a reference to the element.
        var elem = document.getElementById('myCanvas');

        // 判斷是否能取得context
        if (elem && elem.getContext) {
            // 你只能對每一個canvas做initialize一次(getContext).
            // context = canvas . getContext(contextId [, ... ])
            var context = elem.getContext('2d');
            if (context) {
                context.fillStyle = 'pink';
                context.fillRect(0, 0, 50, 50);

                context.fillStyle = '#f00'; // red
                context.fillRect(50, 50, 50, 50);
                context.fillStyle = '#0f0'; // green
                context.fillRect(100, 100, 50, 50);
                context.fillStyle = '#00f'; // blue
                context.fillRect(150, 150, 50, 50);

                // RGBA(red, green, blue, alpha)
                // Alpha1是透明度
                context.fillStyle = 'RGBA(100, 100, 255, 0.2)';
                context.fillRect(50, 50, 150, 150);
            }
        }
    </script>
</body>
</html>

而strokeRect(x, y, w, h)則會使用strokeStyle(顏色), lineWidth(粗細), lineJoin(連接觸樣式),等屬性來決定，其實就是line style。

<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
        <title>Canvas/Line styles</title>
    </head>
<body>
    <canvas id="myCanvas" width="300" height="150">
    Fallback content, in case the browser does not support Canvas.
    </canvas>
    <script type="application/x-javascript">
        // Get a reference to the element.
        var elem = document.getElementById('myCanvas');

        // 判斷是否能取得context
        if (elem && elem.getContext) {
            // 你只能對每一個canvas做initialize一次(getContext).
            // context = canvas . getContext(contextId [, ... ])
            var context = elem.getContext('2d');
            if (context) {
                // The beginPath() starts a new path
                context.beginPath();
                // reset the path to (0, 0)
                context.moveTo(0,0);
                context.strokeStyle = '#f00';

                // lineWidth是線的大小
                context.lineWidth = 1;
                context.strokeRect(0, 0, 20, 20);
                context.lineWidth = 10;
                context.strokeRect(30, 30, 20, 20);

                // LineJoin是連接處(轉角)的樣式
                context.lineJoin = 'bevel';
                context.strokeRect(60, 60, 20, 20);

                context.lineJoin = 'round';
                context.strokeRect(90, 90, 20, 20);

                context.lineJoin = 'miter';
                context.strokeRect(120, 120, 20, 20);
            }
        }
    </script>
</body>
</html>

參考資料：

1. http://dev.opera.com/articles/view/html-5-canvas-the-basics/
2. http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html
3. https://developer.mozilla.org/en/Canvas_tutorial/Using_images
4. http://wiki.moztw.org/%E7%94%A8_Canvas_%E7%95%AB%E5%9C%96
5. http://www.w3school.com.cn/htmldom/dom_obj_canvas.asp

source code：
https://github.com/brook-kuo/JavaScript/tree/master/html5/canvas