STEP1: user space===>read man 2
n = read(fd[0], line, MAXLINE);
STEP2: kernel===>sys_read unistd.h
/* fs/pipe.c */
#define __NR_pipe2 59
__SYSCALL(__NR_pipe2, sys_pipe2)
/* fs/quota.c */
#define __NR_quotactl 60
__SYSCALL(__NR_quotactl, sys_quotactl)
/* fs/readdir.c */
#define __NR_getdents64 61
#define __ARCH_WANT_COMPAT_SYS_GETDENTS64
__SC_COMP(__NR_getdents64, sys_getdents64, compat_sys_getdents64)
/* fs/read_write.c */
#define __NR3264_lseek 62
__SC_3264(__NR3264_lseek, sys_llseek, sys_lseek)
#define __NR_read 63
__SYSCALL(__NR_read, sys_read)
#define __NR_write 64
__SYSCALL(__NR_write, sys_write)
STEP3: read_write.c
SYSCALL_DEFINE3(read, unsigned int, fd, char __user *, buf, size_t, count)//argv:fd, buf, count
{
struct fd f = fdget_pos(fd);//fd-->f
ssize_t ret = -EBADF;
if (f.file) {
loff_t pos = file_pos_read(f.file);//pos出世，拿到此文件当前的pos
ret = vfs_read(f.file, buf, count, &pos);//调用到 vfs_read(), argv:f.file, buf, cout, pos
if (ret >= 0)
file_pos_write(f.file, pos);//一旦vfs_read成功返回，我需要修改f.file中pos的位置,这样内核就一直记录着每个文件的pos
fdput_pos(f);
}
return ret;
}
STEP4: read-->vfs_read(f.file, buf, count, &pos);
这里还没有调用到我们对应设备的fops
ssize_t vfs_read(struct file *file, char __user *buf, size_t count, loff_t *pos)
{
ssize_t ret;
if (!(file->f_mode & FMODE_READ))
return -EBADF;
if (!(file->f_mode & FMODE_CAN_READ))
return -EINVAL;
if (unlikely(!access_ok(VERIFY_WRITE, buf, count)))
return -EFAULT;
ret = rw_verify_area(READ, file, pos, count);
if (ret >= 0) {
count = ret;
if (file->f_op->read)
ret = file->f_op->read(file, buf, count, pos);//调用到file->f_op－>read注意参数.
else if (file->f_op->aio_read)
ret = do_sync_read(file, buf, count, pos);
else
ret = new_sync_read(file, buf, count, pos);
if (ret > 0) {
fsnotify_access(file);
add_rchar(current, ret);
}
inc_syscr(current);
}
return ret;
}
STEP5: 使用读管道的例子.
n = read(fd[0], line, MAXLINE);
const struct file_operations pipefifo_fops = {
.open = fifo_open,
.llseek = no_llseek,
.read = new_sync_read,//会调用到设备的read
.read_iter = pipe_read,
.write = new_sync_write,
.write_iter = pipe_write,
.poll = pipe_poll,
.unlocked_ioctl = pipe_ioctl,
.release = pipe_release,
.fasync = pipe_fasync,
};
调用方STEP4: ret = file->f_op->read(file, buf, count, pos);//调用到file->f_op－>read注意参数.
ssize_t new_sync_read(struct file *filp, char __user *buf, size_t len, loff_t *ppos)
{
struct iovec iov = { .iov_base = buf, .iov_len = len };
struct kiocb kiocb;
struct iov_iter iter;
ssize_t ret;
init_sync_kiocb(&kiocb, filp);
kiocb.ki_pos = *ppos;
kiocb.ki_nbytes = len;
iov_iter_init(&iter, READ, &iov, 1, len);
ret = filp->f_op->read_iter(&kiocb, &iter);//注意参数改变.
if (-EIOCBQUEUED == ret)
ret = wait_on_sync_kiocb(&kiocb);
*ppos = kiocb.ki_pos;
return ret;
}
STEP6:new_sync_read调用方
ret = filp->f_op->read_iter(&kiocb, &iter);//注意参数改变.
pipe_read(struct kiocb *iocb, struct iov_iter *to)；参数在调用方函数中.
STEP: END 回顾调用流程
1.read(fd[0], line, MAXLINE);
2.SYSCALL_DEFINE3(read, unsigned int, fd, char __user *, buf, size_t, count)
3.在2中被调用vfs_read(f.file, buf, count, &pos) ---> 可以参看vfs_open 中会回调open会调用到设备的open,完成filpe和inode的关联
4.在3中被调用ret = file->f_op->read(file, buf, count, pos);
5.对应于4,new_sync_read(struct file *filp, char __user *buf, size_t len, loff_t *ppos)
6.在5中被调用ret = filp->f_op->read_iter(&kiocb, &iter)
7.对应于6，pipe_read(struct kiocb *iocb, struct iov_iter *to)
