linux 0.11 内核学习 bitmap.c

/*
 *  linux/fs/bitmap.c
 *
 *  (C) 1991  Linus Torvalds
 */
/* bitmap.c contains the code that handles the inode and block bitmaps */
#include <string.h>
#include <linux/sched.h>
#include <linux/kernel.h> // 一些内核常用函数的原形定义
/* 将指定地址(addr)处的一块内存清零 */
#define clear_block(addr) \
__asm__("cld\n\t" \
"rep\n\t" \
"stosl" \
::"a" (0),"c" (BLOCK_SIZE/4),"D" ((long) (addr)):"cx","di")
/* 置位指定地址开始的第nr 个位偏移处的比特位 */
#define set_bit(nr,addr) ({\
register int res __asm__("ax"); \
__asm__ __volatile__("btsl %2,%3\n\tsetb %%al": \
"=a" (res):"0" (0),"r" (nr),"m" (*(addr))); \
res;})
/* 复位指定地址addr开始的第nr 位偏移处的比特位 */
#define clear_bit(nr,addr) ({\
register int res __asm__("ax"); \
__asm__ __volatile__("btrl %2,%3\n\tsetnb %%al": \
"=a" (res):"0" (0),"r" (nr),"m" (*(addr))); \
res;})
/* 从addr 开始寻找第1 个0 值比特位，并将其距离addr 的比特位偏移值返回 */
#define find_first_zero(addr) ({ \
int __res; \
__asm__("cld\n" \
"1:\tlodsl\n\t" \
"notl %%eax\n\t" \
"bsfl %%eax,%%edx\n\t" \
"je 2f\n\t" \
"addl %%edx,%%ecx\n\t" \
"jmp 3f\n" \
"2:\taddl $32,%%ecx\n\t" \
"cmpl $8192,%%ecx\n\t" \
"jl 1b\n" \
"3:" \
:"=c" (__res):"c" (0),"S" (addr):"ax","dx","si"); \
__res;})
/* 复位指定逻辑块block （相对于磁盘而言）的逻辑块位图比特位 */
void free_block(int dev, int block)
{
struct super_block * sb;
struct buffer_head * bh;
if (!(sb = get_super(dev))) // 取指定设备dev 的超级块
panic("trying to free block on nonexistent device"); // 设备不存在
// 若逻辑块号小于首个逻辑块号或者大于设备上总逻辑块数
if (block < sb->s_firstdatazone || block >= sb->s_nzones)
panic("trying to free block not in datazone");
bh = get_hash_table(dev,block); // 从hash 表中寻找该块数据
if (bh) // 合法？ 
{
if (bh->b_count != 1) // 只有该进程占据block
{
printk("trying to free block (%04x:%d), count=%d\n",