如何从结构页面获取相关数据的物理地址？ [英] How to get the physical address of the associated data from a struct page?

问题描述

比方说，我们已经有了一个结构页从页面缓存的文件的地址空间。

Let's say we've got a struct page from the address space of a page cached file.

我们怎样才能从这个结构页 4KB的数据的起始物理地址？

How could we get the starting physical address of the 4KB data from this struct page?

我想应该是这样的数据在结构的sk_buff 的指针，但我没有找到它

I suppose there should be something like the data pointer inside struct sk_buff, but I didn't find it.

修改

由于垫子和llya的答案。

Thanks Mat and llya for the answers.

在看答案后，我想第一个问题是确定是否结构页位于 ZONE_NORMAL 或 ZONE_HIGHMEM 。

After looking at the answers, I think the first problem is to identify whether the struct page is located in ZONE_NORMAL or ZONE_HIGHMEM.

在一个文件I / O，当我们没有找到缓存的页面，我们将首先使用分配一个新的页面 page_cache_alloc_cold（）。 page_cache_alloc_cold（）将最后调用 alloc_pages（）它看起来像它会使用 ZONE_HIGHMEM （这在86，是开始于 PAGE_OFFSET + 896M内核内存区）为它的工作。

During a file I/O, when we don't find the cached page, we will at first allocate a new page using page_cache_alloc_cold(). page_cache_alloc_cold() will finally calls alloc_pages() which looks like it will use the ZONE_HIGHMEM (which in x86, is the kernel memory area starting at PAGE_OFFSET+896M) for its job.

所以

• 我想垫的答案是适合 ZONE_NORMAL 页


• 假设我们使用 KMAP（）找到与结构页面相关的4KB数据的起始物理地址，它是正确的，我们应该使用（无符号长）（安培;页）-PAGE_OFFSET 来找到在哪里存储结构本身
的物理地址？

• I think Mat's answer is suitable for pages in ZONE_NORMAL
• Suppose we use kmap() to find the starting physical address of the 4KB data associated with the struct page, is it correct that we should use (unsigned long)(&page)-PAGE_OFFSET to find the physical address where stores the structure itself?

请纠正。

推荐答案

您需要一个页映射到内核内存如下：

You need to map a page into the kernel memory as follows:

void * mapping = kmap_atomic(page, KM_USER0);
// work with mapping...
kunmap_atomic(mapping, KM_USER0);

是必需的这招，因为在Linux上 HighMemory 的概念（见的这链接前）。

This trick is required as there is a HighMemory concept in Linux (see this link for ex.).

UPD：您可以使用 KMAP 而不是 kmap_atomic 在非原子上下文

UPD: You can use kmap instead of kmap_atomic in non-atomic contexts.

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