mmap tutorial

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

->gpi;PRINTK (kern_alert "GPIO =%08x", (int) ugpio);Copy_to_user (void *) arg, (const void *) ugpio,sizeof (Ugpio));Break}Case get_io_dir:{PRINTK (Kern_alert "get_io_dir\r\n");Break}}return 0;}2. At the application layer use the MMAP function at the application layer to obtain the virtual address pointer of the GPIO physical base site, and then use this pointer to read and write the Gpio register, here is a bit of program snippet for everyone to refer

); Mapfd (FD, size); // obtain a piece of memory by using the MMAP method of the FD. // Do not understand. Check man MMAP. After mapfd is complete, the mbase variable points to the starting position of the memory. msize indicates the size of the allocated memory, and MFD indicates File descriptor returned by ashmem_create_region } Memoryheapbase provides several functions to obtain the size and location o

MMAP can map a part of the disk file directly to the memory, so that the location in the file has a corresponding memory address, you can directly use pointers to read and write files without the need for the read/write function. Prototype: # include Void * MMAP (void * ADDR, size_t Len, int Prot, int flag, int filedes, off_t off ); Int munmap (void * ADDR, size_t Len ); The parameters are expla

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

IPC Three communication mechanism refers to: semaphore, shared memory, message queue,signal Volume: Through the operating system of the PV operation to achieve;Shared Memory: Request a piece of memory, process A to write in shared memory, other processes can read out the contents of the shared memory to obtain the information transmitted by process A;Message Queuing: Create a message queue, process a writes to the queue, and process B gets the information that process a transmits by reading the

Preface Work encountered some of the demand for KV storage, such as the recommendation system needs to store a commodity ID corresponding to the similar Product ID list, or a user's browsing the Product ID list, which requires a key value to store. This article describes the storage based on the requirements of a simple implementation of a version, the actual work is much more complex, in order to make the reader easy to understand, based on this analysis of a primary key to String key,value is

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

Mmap function,1. mmap system call The man manual shows that: 1 void * mmap (void * addr, size_t length, int prot, int flags, 2 int fd, off_t offset ); Function: maps the file content to the virtual address space of the process. By reading and modifying the memory, you can read and modify the file without calling read and write; Parameters: Addr: Start addr

1. MmapMmap can map a portion of a disk file directly to memory, so that the location of the file directly has a corresponding memory address, read and write to the file can be directly with the pointer without the need for the Read/write function.Shared memory Exchange data, not switch the power level, fast.Mmap Cons: 1) consumes memory, fragmentation. 2) ordinary documents.Pros: 1) Map speed is fast. 2) can be atomic access to any byte, do not worry about offset.#include void *

I. Overview Memory ing, in short, is to map a memory area of the user space to the kernel space. After the ing is successful, the user's modifications to this memory area can be directly reflected in the kernel space, modifications made to this region by the kernel space also directly reflect the user space. Therefore, if the kernel space First, the driver allocates a piece of memory, and then the user process uses the library function MMAP () to tel

the function is in the stack frame. function static local variables and the spatial allocation of global variables in the data segment. Process but the scope of the two is different. Stackheap code Snippet data segment heap, stack life cycle either the programmer manually frees the heap space. Otherwise, at the end of the process. Second, use Mmap to map the physical address to the virtual address space of the process.

Introduction to Linux mmap function, linuxmmap Function I. Introduction 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:

Mmap maps a file or other object into memory. Mmap can also implement shared memory. mmap function calls enable shared memory between processes by mapping the same file. After the file is mapped to the process address space, the process can manipulate the file like read-write memory. Function prototype: void* mmap(void

Function Description: MMAP maps a file or other objects to the memory. The file is mapped to multiple pages. If the file size is not the sum of the sizes of all pages, the unused space of the last page will be cleared. Munmap performs the opposite operation to delete the object ing of a specific address area. File-based ing, the st_atime of the mapped file may be updated at any time during MMAP and munmap

Initially After reading the memory ing I/O, it means you can understand it, that is, you can directly operate the file and then directly operate through the buffer to reduce the time it takes to call the read and write operations. In addition, the following is an example of copy.However, after I map two files, I can use the memcpy memory replication function to write the files, but this is the operation of the two files, I want to modify a file myself? What should I do when there is only one fil

The advanced driver courses over the past few days are really happy. Block devices and MTD devices are really clear and open-minded.When it's still hot and free, record the MMAP implementation in the S3C2410 framebuffer driver. For more information, seePreviously, MMAP was replaced. There is no concept of how to implement an MMAP in the kernel space.There is no

Mmap,mmap64,munmap---Map or unmap files or devices into memoryvoid *mmap (void* addr,size_t length, int prot, int flags, int fd, off_t offset);void *mmap64 (void* addr,size_t length, int prot, int flags, int fd, off_t offset);int Munmap (void *addr, size_t lenght);Mmap function creates a new mapping in the virtual address space of the the calling process. The sha