linux mmap example

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 $(KERNELDIR) M=$(

Linux system programming: inter-process communication-mmap, linux-mmap Inter-process communication-mmap #include In essence, mmap synchronizes the memory with files on the hard disk. The content in a memory is synchronized to

. #include This reads the contents of the file through read (), ToUpper (), and invokes write () writeback file. Because the file is too small to reflect the disadvantage of Read ()/write (): Frequent access to large files requires multiple Lseek () to determine the location. Each time you edit the read ()/write (), double data in physical memory. Of course, it is not possible to ignore the cost of creating and maintaining mmap () data structures.

call is done by calling the sync function of the ing file. BRK (void * end_data_segement ): Extend the data segment of a processEnd_data_segement specifies the address. This system call is similar to the MMAP implementation method. It also generates a VMA and then specifies its attributes.However, you need to check the validity of the address before this operation, for example, whether the address is great

Memory Allocation in linux: mmap, munmp, brk, mmapbrk Linux virtual memory management has several key concepts: 1. Each process has an independent virtual address space. The virtual address accessed by the process is not a real physical address; 2. The virtual address can be mapped to the physical address through the page table on each process (in the kernel vir

re-establish the shared memory area when there is new communication. Instead, the shared area is maintained until the communication is complete, so that the data content is kept in shared memory and is not written back to the file. Content in shared memory is often written back to a file when it is de-mapped. Therefore, the use of shared memory communication mode is very efficient.The Linux 2.2.x kernel supports a variety of shared memory methods, su

1. Introduction to shared memory The shared memory zone is the fastest form of IPC. data transmission between these processes no longer involves the kernel. In other words, processes no longer transmit data by executing system calls that enter the kernel. That is, each process address space has a shared storage ing area. When this area is mapped to the same real physical address space, data exchange can be performed through this area, for example, th

such a virtual storage space, and establish the VM_AREA_STRUCT structure to pass it to the specific device driver.2. Establish a mapping between the virtual address space and the physical address of the file or device (device-driven completion)The second step in establishing a file map is to establish a mapping between the virtual address and the specific physical address, which is achieved by modifying the Process page table. The Mmap method is a me

structure to pass it to the specific device driver.2. Establish a mapping between the virtual address space and the physical address of the file or device (device-driven completion)The second step in establishing a file map is to establish a mapping between the virtual address and the specific physical address, which is achieved by modifying the Process page table. The Mmap method is a member of the FILE_OPEARTIONS structure:Int (*

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 me

memory in two ways:(1) Memory mapping provided with normal files: applies to any process; At this point, you need to open or create a file and then call Mmap (); The typical calling code is as follows:Fd=open (name, flag, mode); if (fdPtr=mmap (NULL, Len, prot_read| Prot_write, map_shared, FD, 0); There are many features and areas of communication that enable shared memory through

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 (S

In Linux, MMAP and mmap2 are called to create a process address space ing. MMAP and mmap2 are commonly used in the following scenarios: 1. file ing common file I/O operations, read and write the memory after MMAP ing, you can complete file read and write operations, kernel and userspace operations are the same physical

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 implementation on Linux is called by the kernel's BRK system. BRK () is a very simple system call, simply changing the value of the member variable BRK of

establish a mapping between the virtual address and the specific physical address, which is achieved by modifying the Process page table. The Mmap method is a member of the FILE_OPEARTIONS structure:Int (*mmap) (struct file *,struct vm_area_struct *);There are 2 ways to build a page table in Linux:(1) Use Remap_pfn_range to create all page tables at once.int Rem

protection is based on pages. Even if the mapped file has only one byte size, the kernel will allocate a page size memory for the ing. When the size of the mapped file is smaller than the size of a page, the process can access the page size starting with the return address of MMAP () without errors. However, if you access an address space other than a page, an error occurs, which will be further described later. Therefore, the size of the valid addre

" 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 En

Forwarded by: Http://blog.chinaunix.net/uid-26669729-id-3077015.htmlMmap detailed description of Linux memory managementOne. Mmap system call1. Mmap system callMmap maps a file or other object into memory. Files are mapped to multiple pages, and if the size of the file is not the sum of the size of all pages, the space that is not used by the last page will be ze

to implement the Vb2_mem_ops interface. And if you still use the old version of the process, then you need to videobuf_queue_dma_contig_init to provide a videobuf_qtype_ops, because Alloc_vb is the old version of eitherV4l2_memory_mmap is stillv4l2_memory_userptr all to achieveVideobuf_qtype_ops. In contrast, forV4l2_memory_userptr the new version can reduce a certain amount of code, without vb2_mem_ops.Of course, the architecture can be implemented in a variety of ways, the essence of the purp

(void *start, size_t length);3. Virtual Memory Area:The virtual memory area is a homogeneous interval in the virtual address space of the process, that is, a contiguous address range with the same characteristics. The memory image of a process consists of the following parts: program code, data, BSS and stack areas, and memory-mapped regions.The Linux kernel uses the VM_AREA_STRUCT structure to describe the virtual memory area. Its main members:unsig