[英]How to get the physical address of the associated data from a struct page?
Let's say we've got a struct page
from the address space of a page cached file.假设我们从页面缓存文件的地址空间中获得了一个
struct page
。
How could we get the starting physical address of the 4KB data from this struct page
?我们如何从这个
struct page
中获取 4KB 数据的起始物理地址?
I suppose there should be something like the data
pointer inside struct sk_buff
, but I didn't find it.我想
struct sk_buff
中应该有类似data
指针的东西,但我没有找到它。
EDIT编辑
Thanks Mat and llya for the answers.感谢 Mat 和 llya 的回答。
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
.看了答案,我觉得第一个问题就是判断
struct page
是在ZONE_NORMAL
还是ZONE_HIGHMEM
。
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()
.在文件 I/O 期间,当我们找不到缓存页面时,我们将首先使用
page_cache_alloc_cold()
分配一个新页面。 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. page_cache_alloc_cold()
最终会调用alloc_pages()
,看起来它将使用ZONE_HIGHMEM
(在 x86 中,是从PAGE_OFFSET
+896M 开始的 kernel memory 区域)。
So所以
ZONE_NORMAL
ZONE_NORMAL
中的页面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?kmap()
来查找与结构页关联的 4KB 数据的起始物理地址,我们应该使用(unsigned long)(&page)-PAGE_OFFSET
来查找存储结构本身的物理地址是否正确? Please correct.请改正。
You need to map a page
into the kernel memory as follows:你需要把 map 一个
page
变成 kernel memory 如下:
void * mapping = kmap_atomic(page, KM_USER0);
// work with mapping...
kunmap_atomic(mapping, KM_USER0);
This trick is required as there is a HighMemory
concept in Linux (see this link for ex.).这个技巧是必需的,因为 Linux 中有一个
HighMemory
概念(例如,请参见此链接)。
UPD: You can use kmap
instead of kmap_atomic
in non-atomic contexts. UPD:您可以在非原子上下文中使用
kmap
而不是kmap_atomic
。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.