mmap 有什么作用？
这行代码是做什么的？
mmap(NULL, n, PROT_WRITE, MAP_ANON | MAP_PRIVATE, -1, 0);
What does this line of code do?
mmap(NULL, n, PROT_WRITE, MAP_ANON | MAP_PRIVATE, -1, 0);
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man mmap将为您提供帮助。它在进程的虚拟地址空间中创建内存映射。它创建一个匿名映射，这很像使用
malloc来分配n字节的内存。参数为：
NULL- 内核将为映射选择一个地址n- 映射的长度（以字节为单位）PROT_WRITE- 页可以写成MAP_ANON | MAP_PRIVATE- 映射不受文件支持，写入映射的更新是进程私有的-1- 文件描述符；未使用，因为映射不受文件支持0- 文件内开始映射的偏移量 - 再次未使用，因为映射不受文件支持man mmapwill help you here.It creates a memory mapping in the virtual address space of the process. It's creating an anonymous mapping, which is rather like using
mallocto allocatenbytes of memory.The parameters are:
NULL- the kernel will choose an address for the mappingn- length of the mapping (in bytes)PROT_WRITE- pages may be writtenMAP_ANON | MAP_PRIVATE- mapping is not backed by a file, and updates written to the mapping are private to the process-1- the file descriptor; not used because the mapping is not backed by a file0- offset within the file at which to start the mapping - again, not used, because the mapping is not backed by a file它请求 n 字节内存的私有、可写匿名映射。
fork()之后，子进程和父进程将具有独立的映射）；在这种情况下，它本质上是请求一个
n字节的内存块，因此大致相当于malloc(n)（尽管必须使用munmap( )而不是free()，并且它将是页面对齐的）。它还要求内存可写，但不要求其可读，但是可写和不可读内存通常不是底层硬件支持的组合。当单独请求 PROT_WRITE 时，POSIX 允许实现提供也可以读取和/或可执行的内存。It requests a private, writeable anonymous mapping of
nbytes of memory.fork()the child and parent will have independent mappings);In this case, it is essentially requesting a block of
nbytes of memory, so roughly equivalent tomalloc(n)(although it must be freed withmunmap()rather thanfree(), and it will be page-aligned). It's also requesting that the memory be writeable but not requesting that it be readable, however writeable and unreadable memory is typically not a combination supported by the underlying hardware. WhenPROT_WRITEalone is requested, POSIX allows the implementation to supply memory that can also be read and/or executable.