linux-ramdisk.c
/*
* linux/kernel/blk_drv/ramdisk.c
* //－－内存虚拟盘驱动程序
* Written by Theodore Ts'o, 12/2/91
*/
#include <string.h>
#include <linux/config.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <asm/system.h>
#include <asm/segment.h>
#include <asm/memory.h>
#define MAJOR_NR 1
#include "blk.h"
char *rd_start;
int rd_length = 0;
void do_rd_request(void) //－－虚拟盘的请求操作函数
{
int len;
char *addr;
INIT_REQUEST;
addr = rd_start + (CURRENT->sector << 9); //－－虚拟盘地址
len = CURRENT->nr_sectors << 9; //－－占用的内存字节长度值
if ((MINOR(CURRENT->dev) != 1) || (addr+len > rd_start+rd_length)) {
end_request(0);
goto repeat; //－－非法请求，退出
}
if (CURRENT-> cmd == WRITE) {
(void ) memcpy(addr,
CURRENT->buffer,
len);
} else if (CURRENT->cmd == READ) {
(void) memcpy(CURRENT->buffer,
addr,
len);
} else
panic("unknown ramdisk-command");
end_request(1);
goto repeat;
}
/*
* Returns amount of memory which needs to be reserved.
*/
long rd_init(long mem_start, int length) //－－在系统初始化时被init/main.c调用
{ //－－用于确定虚拟盘在物理内存中的具体位置和大小
int i;
char *cp;
blk_dev[MAJOR_NR].request_fn = DEVICE_REQUEST; //－－函数指针指向do_rd_request()
rd_start = (char *) mem_start;
rd_length = length;
cp = rd_start;
for (i=0; i < length; i++) //－－盘区清空
*cp++ = '/0';
return(length);
}
/*
* If the root device is the ram disk, try to load it.
* In order to do this, the root device is originally set to the
* floppy, and we later change it to be ram disk.
*/
void rd_load(void) //－－虚拟盘根文件加载函数
{ //－－在内核设置函数setup()中调用
struct buffer_head *bh;
struct super_block s;
int block = 256; /* Start at block 256 */
int i = 1;
int nblocks;
char *cp; /* Move pointer */
if (!rd_length)
return;
printk("Ram disk: %d bytes, starting at 0x%x/n", rd_length,
(int) rd_start);
if (MAJOR(ROOT_DEV) != 2)
return;
bh = breada(ROOT_DEV,block+1,block,block+2,-1); //－－读根文件系统的基本参数
if (!bh) {
printk("Disk error while looking for ramdisk!/n");
return;
}
*((struct d_super_block *) &s) = *((struct d_super_block *) bh->b_data);
brelse(bh);
if (s.s_magic != SUPER_MAGIC)
/* No ram disk image present, assume normal floppy boot */
return;
nblocks = s.s_nzones << s.s_log_zone_size; //－－试图加载整个根文件系统到内存虚拟盘区
if (nblocks > (rd_length >> BLOCK_SIZE_BITS)) {
printk("Ram disk image too big! (%d blocks, %d avail)/n",
nblocks, rd_length >> BLOCK_SIZE_BITS);
return;
}
printk("Loading %d bytes into ram disk... 0000k",
nblocks << BLOCK_SIZE_BITS);
cp = rd_start;
while (nblocks) { //－－循环操作加载根文件系统映像文件到虚拟盘
if (nblocks > 2)
bh = breada(ROOT_DEV, block, block+1, block+2, -1);
else
bh = bread(ROOT_DEV, block);
if (!bh) {
printk("I/O error on block %d, aborting load/n",
block);
return;
}
(void) memcpy(cp, bh->b_data, BLOCK_SIZE);
brelse(bh);
printk("/010/010/010/010/010%4dk",i);
cp += BLOCK_SIZE;
block++;
nblocks--;
i++;
}
printk("/010/010/010/010/010done /n");
ROOT_DEV=0x0101;
}
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