> For the complete documentation index, see [llms.txt](https://book.bsdcn.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://book.bsdcn.org/man/man9/declare_geom_class.9.md).

# DECLARE\_GEOM\_CLASS.9

`DECLARE_GEOM_CLASS` — GEOM 类声明宏

## 名称

`DECLARE_GEOM_CLASS`

## 概要

```c
#include <geom/geom.h>
```

```c
DECLARE_GEOM_CLASS(class, mod_name);
```

## 描述

`DECLARE_GEOM_CLASS` 宏在 GEOM 中注册 GEOM 类。GEOM 类本身实现一种特定类型的转换。典型的例子包括：MBR 磁盘分区、BSD disklabel 和 RAID5 类。`DECLARE_GEOM_CLASS` 可用于编译内建的 GEOM 类和作为 [kld(4)](/man/man4/kld.4.md) 模块加载的 GEOM 类，它是类注册的唯一官方方式。

`DECLARE_GEOM_CLASS` 的参数如下：

**`class`** 描述 GEOM 类的 `g_class` 结构。

**`mod_name`** 内核模块名（不是类名！）。

`g_class` 结构包含描述类的数据。它们是：

* 类激活时，所有现有的 provider 都提供给 taste。
* 创建新 provider 时，将其提供给 taste。
* 对 provider 的最后一次写访问关闭后，将其提供给重新 taste（在第一次写打开事件时会发送“spoil”）。

**`const char *`** `name` 类名。

**`g_taste_t *`** `taste` 指向用于处理 taste 事件的函数的指针。如果非 `NULL`，则在以下三种情况下调用：

**`g_config_t *`** `config` 此字段不再使用，其功能由 `ctlreq` 字段取代。

**`g_ctl_req_t *`** `ctlreq` 指向用于处理来自用户空间应用程序事件的函数的指针。

**`g_init_t *`** `init` 指向在类注册后立即调用的函数的指针。

**`g_fini_t *`** `fini` 指向在类注销前调用的函数的指针。

**`g_ctl_destroy_geom_t *`** `destroy_geom` 指向在类卸载时为每个 geom 调用的函数的指针。如果未设置此字段，则该类无法卸载。

只有 `name` 字段是必需的；其余均为可选。

## 限制与条件

`g_class` 的字段应始终使用 C99 风格的字段命名进行初始化（参见下面 `example_class` 的初始化方式）。

## 实例

类声明示例。

```c
static struct g_geom *
g_example_taste(struct g_class *mp, struct g_provider *pp,
    int flags __unused)
{
	g_topology_assert();
	[...]
}
static void
g_example_ctlreq(struct gctl_req *req, struct g_class *cp,
    char const *verb)
{
	[...]
}
static int
g_example_destroy_geom(struct gctl_req *req, struct g_class *cp,
    struct g_geom *gp)
{
	g_topology_assert();
	[...]
}
static void
g_example_init(struct g_class *mp)
{
	[...]
}
static void
g_example_fini(struct g_class *mp)
{
	[...]
}
struct g_class example_class = {
	.name = "EXAMPLE",
	.taste = g_example_taste,
	.ctlreq = g_example_ctlreq,
	.init = g_example_init,
	.fini = g_example_fini,
	.destroy_geom = g_example_destroy_geom
};
DECLARE_GEOM_CLASS(example_class, g_example);
```

## 参见

[geom(4)](/man/man4/geom.4.md), [g\_attach(9)](/man/man9/g_attach.9.md), [g\_bio(9)](/man/man9/g_bio.9.md), [g\_consumer(9)](/man/man9/g_consumer.9.md), [g\_data(9)](/man/man9/g_data.9.md), [g\_event(9)](/man/man9/g_event.9.md), [g\_geom(9)](/man/man9/g_geom.9.md), [g\_provider(9)](/man/man9/g_provider.9.md), [g\_provider\_by\_name(9)](/man/man9/g_provider_by_name.9.md), [g\_wither\_geom(9)](/man/man9/g_wither_geom.9.md)

## 作者

本手册页由 Pawel Jakub Dawidek <pjd@FreeBSD.org> 编写。


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://book.bsdcn.org/man/man9/declare_geom_class.9.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.