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abg1984's questions

Martin Hope
abg1984
Asked: 2024-11-27 18:20:20 +0800 CST
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因此，我目前正在学习如何编写内核模块/设备驱动程序，并正在研究以下实现unregister_chrdev_region：

https://elixir.bootlin.com/linux/v6.12/source/fs/char_dev.c#L311

/**
 * unregister_chrdev_region() - unregister a range of device numbers
 * @from: the first in the range of numbers to unregister
 * @count: the number of device numbers to unregister
 *
 * This function will unregister a range of @count device numbers,
 * starting with @from.  The caller should normally be the one who
 * allocated those numbers in the first place...
 */
void unregister_chrdev_region(dev_t from, unsigned count)
{
    dev_t to = from + count;
    dev_t n, next;

    for (n = from; n < to; n = next) {
        next = MKDEV(MAJOR(n)+1, 0);
        if (next > to)
            next = to;
        kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
    }
}

我不明白的是这一行的检查：

https://elixir.bootlin.com/linux/v6.12/source/fs/char_dev.c#L318

if (next > to) next = to;

据我所知，当循环变量等于上限时，循环已经中断to = from + count。什么时候我们会遇到条件的情况if (next > to)？这个条件检查的原因是什么？

linux-kernel