mmap

相同的demo。Ubuntu下运行没问题，在海思开发板运行一直有问题。 期间检查了无数遍参数与mmap的实现代码，完全没问题。后来发现原来是文件系统的问题导致。 mmap的文件存放在SD卡中成功，放在在内置Flash ext目录下出现mmap: Invalid argument ext目录下文件系统为jffs2 SD卡为vfat jffs2会对文件进行压缩，不知道是否是这个因素导致的。 来源： https://blog.csdn.net/chenwr2018/article/details/100972367

I've written a linux driver that ioremaps exports PCI BAR0 for a particular device to a sysfs binary attribute allowing userspace to directly control it. The problem rears when I attempt to MMAP on top of the attribute to directly access that bit of memory (from a userland program). Reads succeed just fine and return expected values, though when I write to that memory it appears to be cached somewhere between the kernel and memory and not delivered to the GMCH root complex (and therefore the device). What I'd like to do is have an implicit write memory barrier after each access. Is there any

Is seems that the mmap interface only supports readline(). If I try to iterate over the object I get character instead of complete lines. What would be the "pythonic" method of reading a mmap'ed file line by line? import sys import mmap import os if (len(sys.argv) > 1): STAT_FILE=sys.argv[1] print STAT_FILE else: print "Need to know <statistics file name path>" sys.exit(1) with open(STAT_FILE, "r") as f: map = mmap.mmap(f.fileno(), 0, prot=mmap.PROT_READ) for line in map: print line # RETURNS single characters instead of whole line The most concise way to iterate over the lines of an mmap is

I'm constantly appending to a file of stock quotes (ints, longs, doubles, etc.). I have this file mapped into memory with mmap. What's the most efficient way to make newly appended data available as part of the memory mapping? I understand that I can open the file again (new file descriptor) and then mmap it to get the new data but that seems to be inefficient. Another approach that has been suggested to me is to pre-allocate the file in 1mb chunks, write to a specific position until reaching the end then ftruncate the file to +1mb. Are there other approaches? Doest Boost help with this? Boost

1.前言 本篇文章的所有例子，基于RHEL6.5平台(linux kernal: 2.6.32-431.el6.i686)。 2.共享内存介绍 前面所讲述的Linux下面的各种进程间通信方式，例如：pipe(管道)，FIFO(命名管道)，message queue(消息队列)，它们的共同点都是通过内核来进行通信(假设posix消息队列也是在内核中实现的，因为posix标准没有规定它的具体实现方式)。向pipe，fifo，message queue写入数据时，需要把数据从用户空间(用户进程)复制到内核，而从这些IPC读取数据时，又需要把数据从内核复制到用户空间。因此，所有的这些IPC方式，都需要在内核与用户进程之间进行2次数据复制，即进程间的通信必须通过内核来传递，如下图所示： 通过内核进行进程间通信(IPC) 共享内存也是一种 IPC ，它是目前最快的IPC，它的使用方式是将同一个内存区映射到共享它的不同进程的地址空间中，这样这些进程间的通信就不再需要通过内核，只需对该共享的内存区域进程操作就可以了。和其他 IPC 不同的是，共享内存的使用需要用户自己进行同步操作。下图是共享内存区 IPC 的通信： 3.映射函数mmap 每个进程都有自己的虚拟地址空间，我们知道除了堆中的虚拟内存我们可以由程序员灵活分配和释放，其他区域的虚拟内存都由系统控制

I got some huge files I need to parse, and people have been recommending mmap because this should avoid having to allocate the entire file in-memory. But looking at 'top' it does look like I'm opening the entire file into the memory, so I think I must be doing something wrong. 'top shows >2.1 gig' This is a code snippet that shows what I'm doing. Thanks #include <stdio.h> #include <stdlib.h> #include <err.h> #include <fcntl.h> #include <sysexits.h> #include <unistd.h> #include <sys/stat.h> #include <sys/types.h> #include <sys/mman.h> #include <cstring> int main (int argc, char *argv[] ) {

We're experimenting with changing SQLite, an embedded database system, to use mmap() instead of the usual read() and write() calls to access the database file on disk. Using a single large mapping for the entire file. Assume that the file is small enough that we have no trouble finding space for this in virtual memory. So far so good. In many cases using mmap() seems to be a little faster than read() and write(). And in some cases much faster. Resizing the mapping in order to commit a write-transaction that extends the database file seems to be a problem. In order to extend the database file,