Linux内核vfs_write函数混乱

Question

I was looking at the old Linux kernel code (3.10.1), particularly the IO path.

So when the IO enters the VFS layer, the function vfs_write() is called.

Here I can see a call to file->f_op->write() , which is a blocking call as the man page of the system call write() says.

The other option in the code is when file->f_op->write pointer is not defined, in that case vfs_write() calls do_sync_write() .

do_sync_write() goes ahead and calls filp->f_op->aio_write() , which is an async call as the man page of aio_write() explains.

Now, my question is, why was the function do_sync_write() named "sync", when it clearly goes on to call an async IO function?

I might be missing something probably, or there was a blunder made here back in those times?

Function definitions for reference,

ssize_t vfs_write(struct file *file, const char __user *buf, size_t count, loff_t *pos)
{
    ssize_t ret;

    if (!(file->f_mode & FMODE_WRITE))
        return -EBADF;
    if (!file->f_op || (!file->f_op->write && !file->f_op->aio_write))
        return -EINVAL;
    if (unlikely(!access_ok(VERIFY_READ, buf, count)))
        return -EFAULT;

    ret = rw_verify_area(WRITE, file, pos, count);
        if (ret >= 0) {
        count = ret;
        file_start_write(file);
        if (file->f_op->write)
            ret = file->f_op->write(file, buf, count, pos);
        else
            ret = do_sync_write(file, buf, count, pos);
        if (ret > 0) {
            fsnotify_modify(file);
            add_wchar(current, ret);
        }
        inc_syscw(current);
        file_end_write(file);
    }

    return ret;
}



ssize_t do_sync_write(struct file *filp, const char __user *buf, size_t len, loff_t *ppos)
{
    struct iovec iov = { .iov_base = (void __user *)buf, .iov_len = len };
    struct kiocb kiocb;
    ssize_t ret;

    init_sync_kiocb(&kiocb, filp);
    kiocb.ki_pos = *ppos;
    kiocb.ki_left = len;
    kiocb.ki_nbytes = len;

    ret = filp->f_op->aio_write(&kiocb, &iov, 1, kiocb.ki_pos);
    if (-EIOCBQUEUED == ret)
        ret = wait_on_sync_kiocb(&kiocb);
    *ppos = kiocb.ki_pos;
    return ret;
}

Answer 1

why was the function do_sync_write() named "sync", when it clearly goes on to call an async IO function?

It calls async function and then waits for its completion with

ret = wait_on_sync_kiocb(&kiocb);

So from the view of the caller of do_sync_write function, the whole function behavior is synced.