mmap mindmap

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

First, it is necessary to state that the new kernel has already adopted Vb2_queue and Vb2_buffer Replace the Videobuf_queue and videobuf_buffer that are often used in older versions of the kernel. The two are mainly used when applying vidioc_reqbuf to the user layer. From the user layer request of the type of memory, the typical two are: V4l2_memory_userptr and V4l2_memory_mmap, the former is located in the user layer, the video output memory address of the driver is provided by the user la

Today Mayuyu encounters two more interesting functions, namely the mmap () and the fmemeopen () functions.First look at the mmap () function, the header file for this function is #include and #include function prototypes are as followsReturn value: If the mapping succeeds, it returns the memory start address of the mapping area, otherwise map_failed (-1) is returned, and the cause of the error is stored in

Original URL: http://www.cnblogs.com/geneil/archive/2011/12/08/2281222.html1.mmap system Callvoid *mmap (void *addr, size_t len, int prot, int flags, int fd, off_t offset);Function: Responsible for mapping the contents of the file to the virtual address space of the process, by reading and modifying the memory to realize the reading and modification of the file, without having to call read and write again;P

I. Overview memory mapping, in short, is to map a section of memory area of user space to the kernel space, after the successful mapping, user changes to this area of memory can be directly reflected to the kernel space, the same, the kernel space for this section of the changes also directly reflect the user space. The efficiency is very high for both kernel space The following is a schematic diagram of an area of memory that maps universal files to user space. figure I: second, the basi

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

MMAP function is a system call in Unix/Linux. Let's take a look at the introduction to MMAP in section 12.2 of UNIX netword programming: The MMAP function maps either a file or a POSIX shared memory object into the address space of a process. We use this function for three purposes: 1. With a regular file to provide memory-mapped I/O 2. With special files to prov

Mmap Implementation Analysis Mmap Implementation Analysis This article does not introduce how to use mmap functions, but analyzes its kernel implementation. There is a lot of information available on the Internet. The essence of Mmap is to assign (or find) a suitable vma for the current process, and then set the cor

Mmap system call (function)void *mmap (void *addr, size_t len, int prot, int flags, int fd, off_t offset)Memory mapping function Mmap, is responsible for the file content mapping to the process of virtual memory space, through the memory of the read and modify, to implement the file read and modify, and do not need to call read, write and other operations.Addr: S

Disk-to-memory mapping is a file mapping, before we say the swap, because This problem makes me very easy to think of Swap,linux swap is the meaning of the swap partition, in the case of memory not enough, the operating system first put the memory and the swap area of the disk to "map", and then the these memory freed up into memory, For the subsequent process of freeing up a piece of memory space, wait until the own process is awakened again, then the memory inside the disk in exchange. Ther

mmap,munmap--#include void*mmap(void*addr, size_tlength,intProtintFlagsintFD, off_t offset);intMunmap (void*addr, size_tlength);intMprotect (void*addr, size_t Len,intProt);intMsync (void*addr, size_tlength,intFlags); mmap, Munmap-Map orUnmap filesorDevices into memory.Storage mapping IO maps a disk file to a buffer in storage space. Then when the data is taken fr

Article Title: Linux mmap File Memory ing mechanism. Linux is a technology channel of the IT lab in China. Includes basic categories such as desktop applications, Linux system management, kernel research, embedded systems, and open source. When describing the concept of file ing, it is inevitable that virtual memory (SVR 4 VM) is involved ). in fact, file ing is the central concept of virtual storage. On the one hand, file ing provides users with a se

The second volume of UNIX Network Programming inter-process communication describes MMAP functions. This function has three main purposes:1. Map a common file to the memory, which is usually used when files need to be read and written frequently. In this way, I/O reading and writing is replaced with memory reading and writing to achieve high performance;2. Anonymous memory ing of special files can provide shared memory space for associated processes;3

I. Overview Memory mapping, in short, is to map a section of memory area of user space to the kernel space, after the successful mapping, user changes to this area of memory can be directly reflected to the kernel space, the same, the kernel space for this section of the changes also directly reflect the user space. The efficiency is very high for both kernel space The following is a schematic diagram of an area of memory that maps universal files to user space. Figure I: Second, the basi

This article describes the POSIX environment uses file mapping IO method of operation, file mapping IO also known as storage mapping IO , for ordinary files, many times it is efficient, it actually reduces the duplication of data, and it can also be used in special places for communication between processes, a way of sharing memory. We can think of a file as a continuous piece of data, from a purely data point of view, which can be understood by any ordinary document. The file map actually corre

same common file. After the normal file is mapped to the process address space, the process can access the same file as the normal memory without having to call read (), write (), and so on. The function prototypes are: #include void *mmap (void *addr, size_t length, int prot, int flags, int fd, off_t offset); Where the parameter addr is the descriptor FD should be mapped to the start address of the process space, when NULL is sp

MongoDB now has two storage engines MMAPv1 and Wiretiger, of course, in addition to these two storage engines there are other storage engines.Such as: Memory Engine: Now the MongoDB version already has, the main cache service, it is mainly to do unit testing. Mongo-rocks: is a key-value engine that is used as a hybrid layer for Facebook's rocksdb Fusion-io: This storage engine is created by SanDisk and he is as far as possible bypassing the operating system's file layer to write

memcpy_fromio (a, B, c) memcpy (a) ,__ io_virt (B), (c ))# Define memcpy_toio (a, B, c) memcpy (_ io_virt (a), (B), (c )) Finally, we need to emphasize the implementation of MMAP functions in the driver. MMAP is used to map a device, which means that an address in the user space is associated with the device memory. This allows the program to read or write data within the allocated address range, it

Simple and effective method: mmap and remap_pfn_range 0x00 background As we all know, modern operating systems use a complex method of memory management for the sake of security and overall planning of hardware, resulting in the concept of physical addresses, logical addresses, virtual addresses, and so on. This part of the content is not mentioned in detail, simply The kernel and user-State processes have different logical address spaces. The page