At the operating system level, the virtual address space seen by each process is independent and there is no intersection between them. Therefore, you need to map different virtual addresses of multiple associated processes to the same physical address space through an intermediate Association.MMAP is a function that maps a file (that is, the physical address space in the memory) to the address space of different processes.I. WriteIt is worth noting that MMA
There are a lot of ways to allocate and manage memory commonly used in C + +, such as smart pointers, STL containers, New/delete, Malloc/free, BRK, SBRK, and so on, and recently studied a kind of memory management method of Unix's lower level mmap/munmap, You need to maintain the allocated virtual memory entirely yourself, without any other auxiliary data structures to help maintain the memory space.First, enter the man
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
a Mmap object when you need a string, such as using the RE module to search for a memory-mapped file. Modify a single character: obj[index] = ' A ', or change the string by slicing: [i1:i2] = ' ... '. The current file location data can be read, and Seek () is positioned to another location in the file.Memory-mapped files are created by the Mmap constructor, which differs in UNIX and Windows. Both need to p
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
Title: Question about mmap? -- Linux general technology-Linux programming and kernel information. The following is a detailed description. At the beginning, I learned about linux programming. I don't know much about some basic issues.
I have read the original form of the mmap function void * mmap (void * addr, size_t length, int prot, int flags, int fd, off_t of
In this example, a character device is used. The device applies for a piece of memory, and file_operations has the MMAP function. In test. C, the MMAP memory can be modified by operating the user memory.
Driver code mmap_demo.c
#include
Makefile
KERNELDIR=/lib/modules/$(shell uname -r)/buildPWD=$(shell pwd)obj-m = mmap_demo.omodules:$(MAKE) -C $(KERNELDIR) M=$(PWD) modulestest: test.cgcc $
Test code
#inc
system call:When a process is created or switched, the system information belonging to the current process is loaded. These system information contains the running space of the current process. When the user program calls Mmap. The function finds the appropriate VMA in the space of the current process to describe the area that it is going to map. The function of this area is to map the contents of the specific file that the file descriptor points to
resources as read and write Ram. To ensure cross-platform portability of drivers, we should use specific functions in Linux to access I/O memory resources rather than through pointers to the core virtual addresses. As on the x86 platform, the functions of read/write I/O are as follows:#define READB (Addr) (* (volatile unsigned char *) __io_virt (addr))#define READW (Addr) (* (volatile unsigned short *) __io_virt (addr))#define READL (Addr) (* (volatile unsigned int *) __io_virt (addr))#define W
" This article declined to reprint , originally from http://990487026.blog.51cto.com"Linux System Development 5 interprocess Communication Pipe () FIFO () mmap () pipe () Pipeline Communication Introduction pipe () parent-child process communication case pipe () using piping has some restrictions pipe () pipe buffer size pipe () read-side non-blocking pipeline FIFO () Pipeline file FIFO () write end/Read End program pipeline file size on disk is 0mmap
and ending addresses of the process snippet, Start_data and End_data are the start and end addresses of the process data segment, and Start_stack is the process stack segment start address , START_BRK is the process dynamic memory allocation start address (the start address of the heap), and a BRK (the current last address of the heap), which is the current terminating address of the dynamic memory allocation.The basic function of C language dynamic memory allocation is malloc (), and the basic
to 0;The prot parameter specifies the access rights for shared memory. The following values may be desirable or: prot_read (readable), prot_write (writable), prot_exec (executable), Prot_none (inaccessible), the value is often set to Prot_read | Prot_write.Flags are specified by the following constant values: map_shared, Map_private, map_fixed, where map_shared (changes are shared, all processes are visible to the modified shared memory), Map_private (the change is private, Only visible to the
/ * Use Mmap to operate the file * /#include #include #include #include #include #include #define FILELENGTHintMainvoid){intFD =-1;/ * The string that will be written to the file * / Charbuf[]="Quick brown fox jumps over the lazy dog";Char*ptr = NULL;/* Open the file mmap.txt and reduce the file length to 0, create it if the file does not exist, and read/write the permission to execute */FD = open ("Mmap.txt", O_RDWR/* Readable/writable */| O_creat/
void *mmap (void *addr, size_t length, int prot, int flags, int fd, off_t offset);function function: Map the contents of the file to a piece of memory (virtual memory), through the memory read and modify, to achieve the file read and modify.Parameter descriptionAddr: Specifies the starting address of the map, usually set to null (indicated by the system).Length: Represents how much part of the file is mapped to memory.PORT: How the Map area is protect
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
"set_io_value\r\n");Break}Case get_io_value:{PRINTK (Kern_alert "get_io_value\r\n");Ugpio = stb_gpio->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 thi
Note: The sys/Mman. h header file does not have to be passed in Linux in windows.
Method Introduction:
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.
Void * MMAP (void * Start, size_t length, int Prot, int flags, int FD, off_t offset); the parameters are
1. Write filesWith open ('?? ' ' r+b ' As F: With contextlib.closing (Mmap.mmap (F.fileno (), size, flags=mmap. map_shared, access=mmap. Access_write)) as mm: = ?? Mm.flush ()2. Key Reminders>>> mmap.ACCESS_READ1>>> mmap.ACCESS_WRITE2>>> mmap.ACCESS_COPY3>>> mmap.ACCESS_READ | mmap.ACCESS_WRITE3In and words, is the access=mmap.ACCESS_READ|mmap.ACCESS_WRITE same as access=mmap.ACCESS_COPY . What do
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