mmap

Inter-process Communication-mmap#include The essence of mmap is to synchronize the memory with the files on the hard disk. The contents of a block of memory are synced to the hard disk file, which maps the files to memory. Therefore, the communication between processes is achieved through the reading and writing of the same file.Parameter explanation:Addr: Specifies where to map the block of memory. A null

http://lwn.net/Articles/28746/ Occasionally, a device driver would need to map an address range into a userprocess ' s space. This mapping can is done into give the process DirectAccess to a device ' I/O memory area, or to the driver ' s DMA buffers. 2.6features a number of changes to the virtual memory subsystem, but, for Mostdrivers, supporing mmap () would be relatively Painless. Using Remap_page_range () There are two techniques in with for imple

In the driver code, we often need to map the hardware address to the virtual memory, which is why we need to learn MMAP! The so-called cutting-edge without mistake, let's calm down and learn this very useful tool. Prototype: void * MMAP (void * Start, size_t length, int Prot, int flags,Int FD, off_t offset ); Parameter: Start address of the ing area. (It is generally recommended to be null so that the kern

Use MMAP/dev/MEM to read and write Linux memory Category: Linux Kernel 114 reading comments (1) Favorites Report Use hexedit/dev/MEM to display information in all physical memory. Use MMAP to map/dev/MEM, and then directly read and write it to implement kernel operations in the user space. Below is a sample I wroteView plain # Include # Include # Include # Include # Include # Include Int ma

Linux provides the memory ing function MMAP, which maps the file content to a memory segment (specifically, virtual memory). By reading and modifying this memory segment, to read and modify files, Let's first look at the MMAP function declaration: Header file: Prototype: void * MMAP (void * ADDR, size_t length, int Prot, int flags, int FD, off_t

1. Application space void *virt_mem = Kzalloc (page_size, Gfp_kernel); 2. Drive Layer----->> implement File_operation interface. Mmap method int Led_drv_mmap (struct file *filp, struct vm_area_struct *vma) { VMA is an information body, the user provides MMAP request//Parameter 1, VMA information carrier//parameter 2, User space virtual start position//Parameter 3, physical address unsigned long add

A process can system invoke mmap () to map the contents of an open file to its user space with the following user interface:Mmap (void *start, size_t length, int prot, int flags, int fd, off_t offset).The parameter fd represents an open file, offset is the starting point in the file, and start is mapped to the start address in the user space, and length is long. There are also two parameters, prot and flags, which are used to access patterns of the ma

achieve the effect of sequential access IO and improve the efficiency of reading text, the results show that multithreading only has a read rate of 380 Mb/s.Why is fread less efficient? Read some information to learn how to access the hard disk in fread/fwrite mode. You must specify the number of data to be read to the kernel, and then copy the obtained content from the kernel buffer pool to the user space; writing also requires a process like this. In this way, when I/O is accessed, the buffer

Mmap: a problem occurs when the file is mapped to the memory and the corresponding method on the window. Our program occupies too much memory and crashes when running on the target machine. Some memory can be mapped to files to save some memory. Make a record for future reference. On linux, use mmap: www.2cto.com 1 int dumpFileDescriptor = open (mmFileName, O_CREAT | O_RDWR, 0755); 2 3 if (dumpFileDescripto

efficient.This allows us to understand that shared memory is the fastest way of IPC (interprocess communication) , and it is also described in the framebuffer display driver that mmap can map framebuffer memory to user space. This allows each AP of an Android device to manipulate the mapped memory to change what is displayed.Mmap () system calls enable shared memory between processes by mapping the same common file. After the normal file is mapped to

same position as they were * * off_t target = 0x7f008800; //gpkcon0 0x7f008800 if (fd = open ("/dev/mem", O_RDWR | O_sync)) = =-1) { printf ("/dev/mem could not being opened.\n"); Perror ("open"); Exit (1); } Else { printf ("/dev/mem opened.\n"); } / * MAP one page * / Map_base = mmap (0, map_size, Prot_read | Prot_write, map_shared, FD, Target ~map_mask); if (map_base = = (void *)-1) { printf ("Memory map failed.\

MMAP () and munmap ()-Unix system functions are closer to the underlying void* mmap(void* addr,size_t size,int prot,int flags, int fd, off_t offset) The ADDR parameter can specify the first address of the ing. Generally, the value 0 is assigned to the kernel. Size is the size of the allocated memory, in the unit of page for ing. Prot is the permission to allocate memory. It is gener

This should be considered to be an IPC, although efficiency may not be as high as other IPC methods.It's easy to see maps that map. Indeed, Mmap is a mapping that maps open files to a contiguous set of memory. The memory can be manipulated to read and write to the file, in turn, that is, it is possible to achieve process communication in this way.The MMAP series involves three functions.void *

1. Memory mapping the so-called memory mapping is to map physical memory into the process's address space, these applications can directly use the input and output of the address space, so as to improve the efficiency of reading and writing. Linux provides the mmap () function to map physical memory. In the driver, the application takes a device file as an object, invokes the Mmap () function, prepares the

Description void *mmap (void *start,size_t length,int prot,int flags,int fd,off_t); Specific parameter meaningStart: Point to the memory start address to map, usually set to NULL, to allow the system to automatically select the address, and the mapping succeeds to return the address.Length: Represents how large portions of a file are mapped to memory.Prot: The protection method of the mapped area. There are several ways to combine the following:Prot_

Normal through the file system access to the value of Ain serial port, you can use Fread and other file IO read/sys/bus/iio/devices/iio:device0/in_voltage*_raw content. But this requires high frequency access to the ADC is very inefficient, the data needs to be copied from the disk to the kernel process space, and then copied to the user process space, consuming unnecessary resources. This problem can be solved by memory innuendo, Mmap can realize the

Access to files on disk, you must consolidate and move files into memory according to certain rules, and then access this file. The order in which the pages of the files to be accessed are arranged intoRadix tree. Assuming that the file is small and there is no memory writeback and access to the entire file, the logically linear organization of this file page is in memoryhas been transformed into a tree-like arrangement--radix tree (which is very important). But the actual

Fsync function.From the above class sub-see, a common fwrite function process, basically after a lot of hardships, the data after several copy, only to reach the destination. Some people have doubts, this will improve performance, but will reduce performance. Let's put this problem in the first place.Some people say that I do not want to fwrite+fflush this combination, I want to write directly to page cache. This is our common file IO call read/write function.These functions are basically a fun

When writing a device driver, if you want to map the device memory to the user space, you need to implement MMAP. by reading the ldd3 introduction above, you have a little understanding of MMAP implementation. This article describes how to use Int remap_pfn_range (struct vm_area_struct * VMA, unsigned long effec_addr, Unsigned long PFN, unsigned long size, pgprot_t prot) function or Int io_remap_page_range

Solemnly declare: This article is written by the author based on my personal understanding. errors are inevitable. Please be prepared! You can reprint, modify, and indicate the source when reprinting! When you run sudo apt-Get update, the system prompts: E: Dynamic MMAP has no space. Increase the size of APT: cache-limit. Current Value: 25165824. (MAN 5 apt. conf), E: Error Handling libsvg-ruby1.8 (newfilever1), E: Problem with mergelist/var/lib/AP