mmap mindmap

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

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

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 of such a kernel is often used, resulting in speed restrictions. One solution is

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

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 the process address space, the process can access the same file as the normal memory without havi

("/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.\n"); Perror ("mmap"); } Else { printf ("Memory

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