mmap

For illustration purposes, this script creates a file mapfile containing the content of the files, given as arguments, prepended by a binary header with a sha1 checksum, that allows for duplication detection on subsequent runs. What's needed here is a hashable ctypes.c_char replacement, that can hold sha1 checksums with minimum fuzz, but not choking on '\0' bytes. # -*- coding: utf8 -* import io import mmap import ctypes import hashlib import logging from collections import OrderedDict log = logging.getLogger(__file__) def align(size, alignment): """return size aligned to alignment""" excess =

The Mmap() syscall in the x/sys/unix package in Golang returns a []byte type, while the underlying syscall actually returns a pointer. How does it do this? More specifically, in this package by a Golang developer, the VirtualAlloc function simply returns a pointer. How can this be converted to a byte slice, the same way as it's done in the Unix package? Using the unsafe package you can do the same thing golang.org/x/sys/unix does in the Mmap method of its unexported mmapper type: // Slice memory layout var sl = struct { addr uintptr len int cap int }{addr, length, length} // Use unsafe to turn

I have the following code, ... char* seg = mmap(0, ...) printf("seg=%x\n", seg); ... The program prints with seg=b7ffd000 . While in gdb (for the same execution), when using p/x seg , it prints $2 = 0x0 . I am confused here. Isn't it the same var seg ? why are the values different. PS: in mmap , the first argument is the preferably address of mapped memory and the return value is the actual address of mapped memory. Now that you've answered my question in the comments, I can answer! The value that you see as the result of the printf is the real address. You are seeing 0 as the value of seg in

开始学习在Linux下视频源捕获驱动框架，也就是V4L2（video4linux）,本次关于v4l2的知识准备主要在于其的官方例程，理解官方例程也就差不多掌握了v4l2的基本内容。例程在： http://blog.chinaunix.net/uid-23983143-id-3351976.html 知识准备： v42视频编程的流程和对文件操作并没有什么本质的不同，大概的流程如下 1.打开视频设备(通常是/dev/video0) 2.获得设备信息。 3.根据需要更改设备的相关设置。 4.获得采集到的图像数据（在这里v4l提供了两种方式，直接通过打开的设备读取数据，使用mmap内存映射的方式获取数据）。 5.对采集到的数据进行操作（如显示到屏幕，图像处理，存储成图片文件）。 6.关闭视频设备。 知道了流程之后，我们就需要根据流程完成相应的函数。 第一步： 那么我们首先完成第1步打开视频设备，需要完成int v4l_open(char *, v4l_device *); 具体的函数如下 #define DEFAULT_DEVICE “/dev/video0” int v4l_open(char *dev , v4l_device *vd) { if(!dev)dev= DEFAULT_DEVICE; if((vd-fd=open(dev,O_RDWR))<0){perror(“v4l

I use a mmap'ed file to share data between processes. The code is like this: struct Shared { int Data; }; int file = open("file.dat", O_RDWR); Shared* shared = static_cast<Shared*>( mmap(0, sizeof(Shared), PROT_READ | PROT_WRITE, MAP_SHARED | MAP_POPULATE, file, 0)); shared->Data++; The questions are: Should I use volatile qualifier ( volatile int Data )? Should I use atomic operations on the shared data ( __sync_fetch_and_add(&(shared->Data), 1) )? For future reference: Volatile: Almost Useless for Multi-Threaded Programming . You should not use volatile when changing an integer from more

mmap() docs mentions flag MAP_UNINITIALIZED, but the flag doesn't seem to be defined. Tried on Centos7, and Xenial, neither distro has the flag defined in sys/mman.h as alleged. Astonishingly, the internet doesn't seem to be aware of this. What's the story? Edit: I understand from the docs that the flag is only honoured on embedded or low-security devices, but that doesn't mean the flag shouldn't be defined... How do you use it in portable code? Google has revealed code where it is defined as 0 in cases where not supported, except in my cases it's not defined at all. In order to understand

x86_64栈和mmap固定映射地址   只需要设置全局变量randomize_va_space 值 为 0 ， 这 个 变 量 默 认 值 为 1 。 用 户 可 以 通 过 设 置/proc/sys/kernel/randomize_va_space 来停用该特性，也可以用如下命令： sudo sysctl -w kernel.randomize_va_space=0 内存的延迟分配   只有在真正访问一个地址的时候才建立这个地址的物理映射，这是 Linux 内存管理的基本思想之一。Linux 内核在用户申请内存的时候，只是给它分配了一个线性区（也就是虚拟内存），并没有分配实际物理内存；只有当用户使用这块内存的时候，内核才会分配具体的物理页面给用户，这时候才占用宝贵的物理内存。内核释放物理页面是通过释放线性区，找到其所对应的物理页面，将其全部释放的过程。 内核数据结构 mm_struct start_code：进程代码段的起始地址 end_code：进程代码段的终止地址 start_stack：进程堆栈段起始地址 start_brk：进程动态内存分配起始地址（堆的起始地址） brk：是动态内存分配当前的终止地址（堆的当前最后地址） Heap 操作相关函数 #include <unistd.h> 系统调用int brk(void *addr); C库函数void *sbrk