Linux-0.11内核分析07：缓冲区与多进程操作文件
1. 缓冲块的进程等待队列
- A为一个读盘进程，目的是将hello.txt中的100字节读入buffer[100]中
- B为一个读盘进程，目的是将hello.txt中的200字节读入buffer[200]中
- C为一个写盘进程，目的是将hello.txt写入字符串”ABCDE”
- 三个进程执行顺序为A–>B–>C，进程间没有父子关系
// 进程A打开文件
--- fs --- open.c --- sys_open() --- (current->filp[fd]=f)->f_count++
|- open_namei(inode)
|- f->f_count=1
|- f->f_inode=inode
// 进程A读取文件
--- fs --- read_write.c --- sys_read() --- file_read()
| |
| |- file_dev.c --- file_read() --- nr=bmap((filp->f_pos)/BLOCK_SIZE)
| | |- bh=bread(nr)
| | |- 将数据拷贝到用户空间
| |
| |- buffer.c --- bread() --- bh=getblk()
| | | //假设有空闲缓冲区
| | |- ll_rw_block(READ,bh)
| | | //缓冲区加锁，开始读硬盘
| | |- wait_on_buffer(bh)//等待读盘完成
| |- wait_on_buffer() --- while (bh->b_lock)
| | sleep_on(&bh->b_wait);
|
|- kernel --- sched.c --- sleep_on(p) --- tmp = *p
| | //备份上一个task_struct，这里为空//备份进程B
| |- *p = current//bh->b_wait=A
| |- current->state = 1
| |- schedule()//调度到进程B//调度到进程0
| |- if (tmp)//唤醒上一个进程这里为空//唤醒进程B
| | tmp->state=0;
|- blk_drv --- ll_rw_block.c --- ll_rw_block() --- make_request(bh)
|- make_request() --- lock_buffer(bh)
|- lock_buffer() --- while (bh->b_lock)//未上锁
| sleep_on(&bh->b_wait);
|- bh->b_lock=1//上锁
//进程A消耗时间片，调度到进程B// 进程B打开文件
--- fs --- open.c --- sys_open() --- (current->filp[fd]=f)->f_count++
| | //f与进程A中的f指向不同的file_table[]
| |- open_namei(inode)
| | //与进程A得到的是同一个inode节点
| |- f->f_count=1
| |- f->f_inode=inode
|
|- namei.c --- open_namei() --- inode=iget(dev,inr)
| | //返回已有的inode节点，没有则重新创建
|- iget() --- 遍历整个inode_table[32]
| 如果dev和inode号不等则continue
| inode->i_count++;
| 返回inode
// 进程B读取文件
--- fs --- read_write.c --- sys_read() --- file_read()
| |
| |- file_dev.c --- file_read() --- nr=bmap((filp->f_pos)/BLOCK_SIZE)
| | |- bh=bread(nr)
| | |- 将数据读入进程空间
| |
| |- buffer.c --- bread() --- bh=getblk()
| | | //得到进程A申请的同一个缓冲块
| | |- ll_rw_block(READ,bh)
| | | //开始读硬盘，缓冲块被锁，挂起
| | |- wait_on_buffer(bh)//等待读盘完成
| |- wait_on_buffer() --- while (bh->b_lock)//已上锁
| | | sleep_on(&bh->b_wait);
| |- getblk() --- if ((bh = get_hash_table(dev,block)))
| | return bh;
|
|- kernel --- sched.c --- sleep_on(p) --- tmp = *p//备份进程A的task_struct //备份进程C // 备份进程B
| |- *p = current//bh->b_wait=B
| |- current->state = 1
| |- schedule()//调度到进程C //调度到进程A // 调度到进程C
| |- if (tmp)//唤醒进程A //唤醒进程C //重复唤醒进程B
| | tmp->state=0;
|- blk_drv --- ll_rw_block.c --- ll_rw_block() --- make_request(bh)
|- make_request() --- lock_buffer(bh)
|- lock_buffer() --- while (bh->b_lock)//进程A已上锁
| sleep_on(&bh->b_wait);
|- bh->b_lock=1
//进程B消耗时间片，切换到进程0// 进程C打开文件
--- fs --- open.c --- sys_open() --- (current->filp[fd]=f)->f_count++
| //f与进程B中的f指向不同的file_table[]
|- open_namei(inode)
| //与进程B得到的是同一个inode节点
|- f->f_count=1
|- f->f_inode=inode
// 进程C写入文件
--- fs --- read_write.c --- sys_write() --- file_write()
| |
| |- file_dev.c --- file_write() --- block = create_block(pos/BLOCK_SIZE)
| | |- bh=bread(block)
| | |- 将数据写入bh
| |
| |
| |- buffer.c --- bread() --- bh=getblk()
| | | //得到进程A申请的同一个缓冲块
| | |- ll_rw_block(READ,bh)
| | | //开始读硬盘，缓冲块被锁，挂起
| | |- wait_on_buffer(bh)//等待读盘完成
| |- wait_on_buffer() --- while (bh->b_lock)//已上锁
| | | sleep_on(&bh->b_wait);
| |- getblk() --- if ((bh = get_hash_table(dev,block)))
| | return bh;
|
|- kernel --- sched.c --- sleep_on(p) --- tmp = *p
| | //备份进程B的task_struct //备份进程C
| |- *p = current//bh->b_wait=C
| |- current->state = 1
| |- schedule()//调度到进程0 //调度到进程B
| |- if (tmp)//唤醒进程B //重复唤醒进程C
| | tmp->state=0;
|- blk_drv --- ll_rw_block.c --- ll_rw_block() --- make_request(bh)
|- make_request() --- lock_buffer(bh)
|- lock_buffer() --- while (bh->b_lock)//进程A已上锁
| sleep_on(&bh->b_wait);
|- bh->b_lock=1//再次上锁
//进程C消耗时间片，消耗完毕后进入进程0执行//进程A读盘完毕，发生硬盘中断
--- kernel --- blk_drv --- hd.c --- write_intr() --- end_request(1)
| |
| |- blk.h --- end_request() --- unlock_buffer()
| |- unlock_buffer() --- bh->b_lock=0//bh解锁
| |- wake_up(&bh->b_wait)
|- sched.c --- wake_up(p) --- (**p).state=0//唤醒进程C//进程C读盘完毕，发生硬盘中断
--- kernel --- blk_drv --- hd.c --- write_intr() --- end_request(1)
| |
| |- blk.h --- end_request() --- unlock_buffer()
| |- unlock_buffer() --- bh->b_lock=0//bh解锁
| |- wake_up(&bh->b_wait)
|- sched.c --- wake_up(p) --- (**p).state=0//唤醒进程A//进程B读盘完毕，发生硬盘中断
--- kernel --- blk_drv --- hd.c --- write_intr() --- end_request(1)
| |
| |- blk.h --- end_request() --- unlock_buffer()
| |- unlock_buffer() --- bh->b_lock=0//bh解锁
| |- wake_up(&bh->b_wait)
|- sched.c --- wake_up(p) --- (**p).state=0//唤醒进程B总体执行顺序
进程A: bh->b_lock=1 --- 设置硬盘中断 --- tmp=NULL --- bh->b_wait=A --- A.state=1 --- 切换到进程B --- tmp=B --- bh->b_wait=A --- A.state=1 --- 切换到进程0 --- tmp->state=0 --- 将bh数据读入进程空间 --- 等待时间片耗尽，切换到进程B 进程B: tmp=A --- bh->b_wait=B --- B.state=1 --- 切换到进程C --- tmp.state=0 --- tmp=C --- bh->b_wait=B --- B.state=1 --- 切换到进程A --- tmp.state=0 --- bh->b_lock=1 --- 设置硬盘中断 --- tmp=A --- bh->b_wait=B --- B.state=1 --- 切换到进程C --- tmp.state=0 --- 将bh数据读入进程空间 --- 等待时间片耗尽，切换到进程A 进程C: tmp=B --- bh->b_wait=C --- C.state=1 --- 切换到进程0 --- tmp.state=0 --- bh->b_lock=1 --- 设置硬盘中断 --- tmp=C --- bh->b_wait=C --- C.state=1 --- 切换到进程B --- tmp.state=0 --- tmp=B --- bh->b_wait=C --- C.state=1 --- 切换到进程0 --- tmp.state=0 --- 将数据写入bh --- 等待时间片耗尽，切换到进程B 硬盘中断：bh->b_lock=0 --- C.state=0 --- 切换到进程C --- bh->b_lock=0 --- A.state=0 --- 切换到进程A --- bh->b_lock=0 --- C.state=0 --- 切换到进程C
2. 多进程操作文件综合实例
- 进程A是一个写盘进程，目的是往hello1.txt文件中写入”ABCDE”
- 进程B是一个写盘进程，目的是往hello2.txt文件中写入”ABCDE”
- 进程C是一个读盘进程，目的是从hello3.txt文件中读20000字节到buffer中
- 三个进程执行顺序为A–>B–>C，进程间没有父子关系
- 假设进程A执行时，所有空闲的缓冲块都是脏的，且没加锁
//进程A
--- fs --- buffer.c --- bread() --- bh=getblk()
| | |
| | |- ll_rw_block(READ,bh)
| | |
| | |- wait_on_buffer(bh)
| |- wait_on_buffer() --- while (bh->b_lock)
| | | sleep_on(&bh->b_wait);
| |- getblk() --- 找到空闲，无锁，脏的缓冲区bh
| | |- while(bh->b_dirt){
| | | sync_dev(bh->b_dev);
| | | wait_on_buffer(bh);
| | | }
| | |-
| |
| |- sync_dev(dev) --- 遍历所有缓冲块，如果对应设备缓冲块是脏的
| | ll_rw_block(WRITE,bh);
| //将所有脏的缓冲块都放入请求队列，直到请求队列满
|
|- kernel --- blk_drv --- ll_rw_block.c --- ll_rw_block() --- make_request(bh)
|- make_request() --- lock_buffer(bh)
| |- 在request[32]中找到空闲请求项req
| |- 如果没有空闲请求项
| | sleep_on(&wait_for_request)
| | //切换到进程B
| | 返回1，重新查找
| |- req->bh=bh
| |- add_request(req)
|- lock_buffer() --- while (bh->b_lock)
| | sleep_on(&bh->b_wait);
| |- bh->b_lock=1
|- add_request() --- if (req->bh)
| req->bh->b_dirt=0;
| //去除脏的标志
|- if (!(tmp = dev->current_request)){
| dev->current_request = req;
| (dev->request_fn)();
| return;
| }
| //当前设备没有执行请求时，执行新请求
|- req->next=tmp->next;
|- tmp->next=req;
| //否则将新请求插入请求队列
//这里将刚刚释放的请求项加入队列//进程B
--- fs --- buffer.c --- bread() --- bh=getblk()
| | |
| | |- ll_rw_block(READ,bh)
| | |
| | |- wait_on_buffer(bh)
| |- wait_on_buffer() --- while (bh->b_lock)
| | | sleep_on(&bh->b_wait);
| | | //切换到进程C//切换到进程A
| |- getblk() --- 找到空闲，有锁，干净的缓冲区bh
| | | //该缓冲区是刚刚由进程A上锁并设置为干净的
| | |- wait_on_buffer(bh)//等待解锁//重新等待解锁
| | |- 检测到bh非空闲，返回0执行
| | |
|
|- kernel --- blk_drv --- ll_rw_block.c --- ll_rw_block() --- make_request(bh)
|- make_request() --- lock_buffer(bh)
| |- 在request[32]中找到空闲请求项req
| |- 如果没有空闲请求项
| | sleep_on(&wait_for_request)
| | //切换到进程B
| | 返回1，重新查找
| |- req->bh=bh
| |- add_request(req)
|- lock_buffer() --- while (bh->b_lock)
| | sleep_on(&bh->b_wait);
| |- bh->b_lock=1
|- add_request() --- if (req->bh)
| req->bh->b_dirt=0;
| //去除脏的标志
|- if (!(tmp = dev->current_request)){
| dev->current_request = req;
| (dev->request_fn)();
| return;
| }
| //当前设备没有执行请求时，执行新请求
|- req->next=tmp->next;
|- tmp->next=req;
| //否则将新请求插入请求队列//进程C
--- fs --- buffer.c --- bread() --- bh=getblk()
| | |
| | |- ll_rw_block(READ,bh)
| | | //将读盘请求加入请求队列中
| | |- wait_on_buffer(bh)
| |- wait_on_buffer() --- while (bh->b_lock)
| | | sleep_on(&bh->b_wait);
| | | //切换到进程0//切换到进程B
| |- getblk() --- 找到空闲，有锁，干净的缓冲区bh
| | | //该缓冲区和进程B获取的是同一个
| | |- wait_on_buffer(bh)//等待解锁
| | |- bh->b_count=1
| | | //bh变为非空闲缓冲块
| | |- bh->b_dirt=0//干净的
|
|- kernel --- blk_drv --- ll_rw_block.c --- ll_rw_block() --- make_request(bh)
|- make_request() --- lock_buffer(bh)
| |- 在request[32]中找到空闲请求项req
| |- 如果没有空闲请求项
| | sleep_on(&wait_for_request)
| | //切换到进程B
| | 返回1，重新查找
| | //从反向查找，第一个请求可以用于读
| |- req->bh=bh
| |- add_request(req)
|- lock_buffer() --- while (bh->b_lock)
| | sleep_on(&bh->b_wait);
| |- bh->b_lock=1
|- add_request() --- if (req->bh)
| req->bh->b_dirt=0;
| //去除脏的标志
|- if (!(tmp = dev->current_request)){
| dev->current_request = req;
| (dev->request_fn)();
| return;
| }
| //硬盘还在读，插入请求队列
|- req->next=tmp->next;
|- tmp->next=req;//硬盘中断
--- kernel --- blk_drv --- hd.c --- write_intr() --- end_request(1)
| |
| |- blk.h --- end_request() --- unlock_buffer()
| | |- wake_up(&wait_for_request)
| | | //唤醒进程A
| | |- CURRENT->dev = -1
| | //释放请求项
| |- unlock_buffer() --- bh->b_lock=0//bh解锁
| |- wake_up(&bh->b_wait)
| //唤醒进程C
|- sched.c --- wake_up(p) --- (**p).state=0- 由于进程C的时间片多于进程A，因此切换到进程C执行