2006年二月月 发布的文章

好博客值几文?

以前我对博客的理解较简单,就是自己在网络上的一处’栖息地’,用来间歇地发发牢骚、谈谈感受罢了。至于Blog的’价值’自己倒没有真正想过,今天试用了一把’博客价值评估工具’,呵呵,结果我的博客价值’9562 RMB’^_^.

除了上面提到的’博客价值评估工具‘外,网络上还有很多这种工具,其中比较著名的有’How Much Is My Blog Worth?‘等。不同的工具由于其评估的算法不一致,从而你的博客的价值也就不同。当然这些工具的娱乐成份较大,不必对结果太过斤斤计较。

在这个世界,几乎任何事情都能和’钱’挂钩。博客也不例外。如何利用博客赚钱是现在很多人讨论的话题。不信你就Google一下,各种’琳琅满目’的博客赚钱技巧足以让你眼花缭乱。什么样的博客才能吸引众商家的眼球呢?毫无疑问,访问量大的博客站点,诸如’老徐‘(短短100多天,1000万的点击率,我想这个记录在今后的很长一段时间内都无人能撼动了)、’Keso‘等。而利用Blog赚钱的最直接途径就是在Blog上贴广告。谁也不能阻止博客名人去赚钱,但是赚钱时还是要谨慎的,因为常常由于’分赃不均’而导致一些不愉快的事情发生。这不’老徐’就因为这个与BSP(Blog Service Provider)新浪网发生了一点儿小小的’矛盾‘。

其实在大多数人整天想着如何用博客赚钱的同时,他们并没有意识到博客的真实价值所在。博客的真实价值在哪?其实就是你在刚开通你的第一个博客站点时的想法。我想绝大多数Blogger的初衷不是为了赚钱,所以在这里我们可以回答题目中所提到的问题:好博客,’一文不值’(反之则不成立) — 好博客需要的是更多的关注和沟通,而不是去要求你的’Fans’去点击那些满屏飞舞的小广告。

Compressed 'head.S'

Why do we do this? Don’t ask me.. Incomprehensible are the ways of bootloaders.
                             — comments in arch/i386/boot/compressed/misc.c

There are two ‘head.S’ in linux source package. One is in $(Linux-2.6.15.3_dir/arch/i386/boot/compressed and the other one is in $(Linux-2.6.15.3_dir/arch/i386/kernel. The first one will be analyzed in this artical. Before we go ahead, let’s show a news of linux, that is ‘Army leans toward Linux for FCS(Future Combat System)’.

The first ‘head.S’ is also called ‘compressed head’, which used to decompress the kernel image. Different from those code before, we are now in 32-bit protected mode with paging disabled. The ‘compressed head’ starts from ‘startup_32′.

.text /* ! here just ‘.text’, without ‘.code16′ assembly directive */
.globl startup_32
 
startup_32:
 /*
  * ! clear direction flag
  * ! and clear interrupt flag
  */
 cld
 cli

 /*
  * ! all other segment registers are
  * ! reloaded after protected mode enabled
  * ! __BOOT_DS = 0×18
  */
 movl $(__BOOT_DS),%eax
 movl %eax, %ds
 movl %eax, %es
 movl %eax, %fs
 movl %eax, %gs

 /*
  * ! lss – load full pointer from memory
  * !       to register
  * ! and here ‘ss:esp = stack_start’
  */
 lss stack_start,%esp

 /*
  * ! EAX = 0;
  * ! do {
  * !     DS:[0] = ++EAX;
  * ! } while (DS:[0x100000] == EAX);
  */
 xorl %eax, %eax
1: incl %eax  # check that A20 really IS enabled
 movl %eax, 0×000000 # loop forever if it isn’t
 cmpl %eax, 0×100000
 je 1b

After reload the segment registers, the ‘compressed head’ clears the ‘eflags’ register and fills the kernel bss(the area of uninitialized data of the kernel identified by the _edata and _end symbols) with zeros. Then the decompressed process begins.

 /*
  * ! %esi has been loaded in ‘setup.S’ with ‘INITSET << 4′
  * ! ‘subl $16,%esp’ used to store the first arg, that is
  * ! struct moveparams {
  * !     uch *low_buffer_start;
  * !     int lcount;
  * !     uch *high_buffer_start;
  * !     int hcount;
  * ! } mv;
  * ! the second arg is the %esi which indicates the position
  * ! of the real-mode data
  */
 subl $16,%esp # place for structure on the stack
 movl %esp,%eax
 pushl %esi # real mode pointer as second arg
 pushl %eax # address of structure as first arg

 /*
  * ! if (!decompress_kernel(&mv, esi)) {         // return value in AX
  * !    restore esi from stack;
  * !    ebx = 0;
  * !    goto __BOOT_CS: $__PHYSICAL_START;
  * !    // see linux/arch/i386/kernel/head.S:startup_32
  * ! }
  * ! ‘decompress_kernel’ is coded in
  * ! $(linux-2.6.15.3_dir)/arch/i386/boot/compressed/misc.c
  *
/
 call decompress_kernel
 orl  %eax,%eax
 jnz  3f
 popl %esi # discard address
 popl %esi # real mode pointer
 xorl %ebx,%ebx
 ljmp $(__BOOT_CS), $__PHYSICAL_START

3:
 /*
  * ! move move_rountine_start..move_routine_end to 0×1000
  * ! both the two functions are defined in the tail of
  * ! this file
  */
 movl $move_routine_start,%esi
 movl $0×1000,%edi
 movl $move_routine_end,%ecx
 subl %esi,%ecx
 addl $3,%ecx
 shrl $2,%ecx
 cld
 rep
 movsl

 /*
  * ! Do preparation for ‘move_routine_start’:
  * ! set the parameters
  * ! ebx = real mode pointer
  * ! esi = mv.low_buffer_start
  * ! ecx = mv.lcount
  * ! edx = mv.high_buffer_start
  * ! eax = mv.hcount
  * ! edi = $__PHYSICAL_START
  */
 popl %esi # discard the address
 popl %ebx # real mode pointer
 popl %esi # low_buffer_start
 popl %ecx # lcount
 popl %edx # high_buffer_start
 popl %eax # hcount
 movl $__PHYSICAL_START,%edi
 cli  # make sure we don’t get interrupted

 /*
  * ! jump to physical address: __BOOT_CS:0×1000
  * ! where the move_routine_start function stays
  */
 ljmp $(__BOOT_CS), $0×1000 # and jump to the move routine

 /*
  * ! the control has been transfered to ‘move_routine_start’
  */
move_routine_start:
 movl %ecx,%ebp
 shrl $2,%ecx
 rep
 movsl
 movl %ebp,%ecx
 andl $3,%ecx
 rep
 movsb
 movl %edx,%esi
 movl %eax,%ecx # NOTE: rep movsb won’t move if %ecx == 0
 addl $3,%ecx
 shrl $2,%ecx
 rep
 movsl
 movl %ebx,%esi # Restore setup pointer
 xorl %ebx,%ebx
 ljmp $(__BOOT_CS), $__PHYSICAL_START
move_routine_end:

In ‘move_routine_start’, we perform the operations as follows:
(1) move mv.low_buffer_start to $__PHYSICAL_START, (mv.lcount >> 2) words;
(2) move/append (mv.lcount & 3) bytes;
(3) move/append mv.high_buffer_start, ((mv.hcount + 3) >> 2) words.

After move the decompressed kernel image to its right place, the control will be transfered to physical address:’$(__BOOT_CS):$__PHYSICAL_START’, where the second ‘head.S’ stays.

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