mmap example

fifth parameter of the mmap. Shm_unlink () functionFunction: Delete a shared memory areaHeader files: #include Function prototype: int shm_unlink (const char *name);Parameter: Name of the shared memory areaReturn value: Successfully returned 0, error returned-1The Shm_unlink function removes the name of a shared memory area object, and deleting a name only prevents subsequent Open,mq_open or Sem_open calls from succeeding. You can refer to this artic

process inherits the mapped store, but the new program after exec does not inherit.The following is an example of copying files using storage map Io, which may have different CPU times for users and systems under different operating systems than read/write, but the clock time is significantly faster than read/write. Because: When using read and write, the data is copied from the kernel buffer read to the application buffer, then the data in the appli

after munmap. among them, flags can be MS_SYNC, MS_ASYNC, MS_INVALIDATE, and MS_SYNC must be returned after the write-back is complete. MS_ASYNC will return immediately after the write-back request is sent, MS_INVALIDATE: Use the write-back content to update other Mappings of the file. this system call is done by calling the sync function of the ing file. Brk (void * end_data_segement ): Extend the data segment of a process to the address specified by end_data_segement. The system call is simil

Note: The android underlying malloc is swapped for mmap to get memory, the acquired memory can be added to the tag, so that the meminfo for analysis, you can view the memory of the tag separately for analysis.One. 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

Reprinted from Http://blog.chinaunix.net/uid-26669729-id-3077015.htmlOne. 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 zeroed out. Munmap performs the opposite operation by deleting the object mappings for a specific

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

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

anonymous memory mapping is used, MAP_ANONYMOUS,FD is set to-1 in flags. Some systems do not support anonymous memory mappings, you can use fopen to open the/dev/zero file.The file can then be mapped to the same effect as an anonymous memory map.Offset: File-mapped offsets, usually set to 0, represent the corresponding starting from the front of the file, and offset must be an integer multiple of page_size.return value:If the mapping succeeds, it returns the memory start address of the mapping

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

" 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

unsigned short *) __io_virt (addr) = (b))#define Writel (B,ADDR) (* (volatile unsigned int *) __io_virt (addr) = (b))#define MEMSET_IO (A,b,c) memset (__io_virt (a), (b), (c))#define 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 want to emphasize the implementation of the MMAP function in the driver. Mapping a device with mmap

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 the MM_STRUCT structure.The

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

belonging to different address spaces actually correspond to the same physical page. One Party modifies the data and the other party can see the changes in real time. General application scenarios are embedded devices, such as refresh the LED display screen and record a large amount of sensor data. This requires developers to implement mmap logic simultaneously in their own drivers and user code. First, provide the following interface functions in t

map_anonymous: The contents of the mapped area are initialized to 0. Not related to any file. If this parameter is referred to. FD and offset are ignored. FD: File descriptor (file) offset: The file's starting position (file) return value: map_failed error errno is set to return the first address of the mapped area. intMunmap (void*addr, size_t length); function: Release the file-to-memory mapping parameter: Addr:mmap (2The return value of length: Specifies the size of the mapped area. return v

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 memory; while regular file read and write op

Http://blog.csdn.net/edwardlulinux/article/details/8604400 Many articles have analyzed the implementation principle of MMAP. From the logic of the code, I always feel that the read/write ing area after MMAP is not associated with the common read/write areas. Have to have questions: 1. What is the difference between reading and writing in the ing areas after the common read/write and

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 zeroed out. Munmap performs the opposite operat

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

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