在linux中，如何为内存区域创建文件描述符 [英] In linux , how to create a file descriptor for a memory region

问题描述

我有一些程序可以处理文件或内存缓冲区中的某些数据.我想提供统一的方式来处理这些情况.

I have some program handling some data either in a file or in some memory buffer. I want to provide uniform way to handle these cases.

我可以:1)映射文件，以便我们可以将它们作为内存缓冲区统一处理； 2)使用fopen和fmemopen创建FILE *，以便像FILE *一样统一访问它们.

I can either 1) mmap the file so we can handle them uniformly as a memory buffer; 2) create FILE* using fopen and fmemopen so access them uniformly as FILE*.

但是，我不能使用上述任何一种方法.我需要将它们都当作文件描述符处理，因为我使用的其中一个库仅采用文件描述符，并且对文件描述符执行mmap.

However, I can't use either ways above. I need to handle them both as file descriptor, because one of the libraries I use only takes file descriptor, and it does mmap on the file descriptor.

所以我的问题是，给定一个内存缓冲区(我们可以假定它与4K对齐)，我们能否获得由该内存缓冲区支持的文件描述符?我在其他问题中看到popen是一个答案，但我认为popen中的fd不能被映射.

So my question is, given a memory buffer (we can assume it is aligned to 4K), can we get a file descriptor that backed by this memory buffer? I saw in some other question popen is an answer but I don't think fd in popen can be mmap-ed.

推荐答案

您无法轻松地从某些内存区域"创建文件描述符(除了C标准库之外，这没有帮助).但是，您可以创建共享内存区域，以获取文件描述符作为回报.

You cannot easily create a file descriptor (other than a C standard library one, which is not helpful) from "some memory region". However, you can create a shared memory region, getting a file descriptor in return.

来自 shm_overview(7):

shm_open(3)
创建并打开一个新对象，或打开一个现有的对象.这类似于open(2).呼叫返回文件描述符，以供下面列出的其他接口使用.

shm_open(3)
Create and open a new object, or open an existing object. This is analogous to open(2). The call returns a file descriptor for use by the other interfaces listed below.

列出的接口中有mmap，这意味着您可以像对普通文件进行内存映射一样，对内存进行内存映射".

Among the listed interfaces is mmap, which means that you can "memory map" the shared memory the same as you would memory map a regular file.

因此，在两种情况下(文件或内存缓冲区)都使用mmap应该可以无缝运行，如果仅由您控制内存缓冲区"的创建.

Thus, using mmap for both situations (file or memory buffer) should work seamlessly, if only you control creation of that "memory buffer".

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