/*
* bread_page reads four buffers into memory at the desired address. It's
* a function of its own, as there is some speed to be got by reading them
* all at the same time, not waiting for one to be read, and then another
* etc. This also allows us to optimize memory usage by sharing code pages
* and filesystem buffers..
*/
unsigned long bread_page(unsigned long address, dev_t dev, int b[], int size, int prot)
{
struct buffer_head * bh[8];
unsigned long where;
int i, j;
if (!(prot & PAGE_RW)) {
where = try_to_share_buffers(address,dev,b,size);
if (where)
return where;
}
++current->maj_flt;
for (i=0, j=0; j<PAGE_SIZE ; i++, j+= size) {
bh[i] = NULL;
if (b[i])
bh[i] = getblk(dev, b[i], size);
}
read_buffers(bh,i);
where = address;
for (i=0, j=0; j<PAGE_SIZE ; i++, j += size,address += size) {
if (bh[i]) {
if (bh[i]->b_uptodate)
COPYBLK(size, (unsigned long) bh[i]->b_data,address);
brelse(bh[i]);
}
}
return where;
}
/*
* bread_page reads four buffers into memory at the desired address. It's
* a function of its own, as there is some speed to be got by reading them
* all at the same time, not waiting for one to be read, and then another
* etc.
*/
void bread_page(unsigned long address,int dev,int b[4])
{
struct buffer_head * bh[4];
int i;
for (i=0 ; i<4 ; i++)
if (b[i]) {
if (bh[i] = getblk(dev, b[i], 1024))
if (!bh[i]->b_uptodate)
ll_rw_block(READ,bh[i]);
} else
bh[i] = NULL;
for (i=0 ; i<4 ; i++,address += BLOCK_SIZE)
if (bh[i]) {
wait_on_buffer(bh[i]);
if (bh[i]->b_uptodate)
COPYBLK((unsigned long) bh[i]->b_data,address);
brelse(bh[i]);
}
}
//// 读设备上一个页面（4 个缓冲块）的内容到内存指定的地址。
void
bread_page( unsigned long address, int dev, int b[4] )
{
struct buffer_head *bh[4];
int i;
// 循环执行4 次，读一页内容。
for( i = 0; i < 4; i++ )
{
if( b[i] )
{
// 取高速缓冲中指定设备和块号的缓冲区，如果该缓冲区数据无效则产生读设备请求。
if( bh[i] = getblk( dev, b[i] ) )
{
if( !bh[i]->b_uptodate )
{
ll_rw_block( READ, bh[i] );
}
}
}else
{
bh[i] = NULL;
}
}
// 将4 块缓冲区上的内容顺序复制到指定地址处。
for( i = 0; i < 4; i++, address += BLOCK_SIZE )
{
if( bh[i] )
{
wait_on_buffer( bh[i] ); // 等待缓冲区解锁(如果已被上锁的话)。
if( bh[i]->b_uptodate ) // 如果该缓冲区中数据有效的话，则复制。
{
COPYBLK( (unsigned long)bh[i]->b_data, address );
}
brelse( bh[i] ); // 释放该缓冲区。
}
}
}