mmap file

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 su

effectively manage user data and read/write efficiency. User data is not directly from the application layer, read or write disks and storage media, but is divided by applications on a layer-by-layer basis, different functions correspond to each layer. In the final interaction, the disk operation is triggered at the most appropriate time. Write Data to disks and storage media using an I/O driver. The management of page cache is emphasized here. The cache should be designed for page management.

Now, in Linux often can be seen in the user space to write the driver, such as x server, some vendors private drive, etc., which means that user space has access to the hardware, this is usually through the MMAP device memory map to the user process space, This allows the user to gain access to the hardware by reading and writing these memory. The kernel typically buffers I/O operations for better performance, but also provides direct I/O and asynchro

Descriptor Specific structure, please refer to the following figure The memory map is now known to map the device address to the process space address (note: Not all memory mappings are mapped to the process address space, Ioremap is mapped to the kernel virtual space, mmap is mapped to the process virtual address), essentially allocating a vm_area_ The struct structure is added to the address space of the process, that is, mapping the device addres

How the kernel guarantees that each process addresses the memory page of the same shared memory area1. Page cache and swap cache pages: a physical page of an accessed file resides in the page cache or swap cache, and all the information for a page is described by a struct page. There is a field in the struct page that is pointer mapping, which points to a struct ADDRESS_SPACE type structure. All pages in the page cache or swap cache are differentiated

Today Mayuyu encounters two more interesting functions, namely the mmap () and the fmemeopen () functions.First look at the mmap () function, the header file for this function is #include and #include function prototypes are as followsReturn value: If the mapping succeeds, it returns the memory start address of the mapping area, otherwise map_failed (-1) is retu

Original URL: http://www.cnblogs.com/geneil/archive/2011/12/08/2281222.html1.mmap system Callvoid *mmap (void *addr, size_t len, int prot, int flags, int fd, off_t offset);Function: Responsible for mapping the contents of the file to the virtual address space of the process, by reading and modifying the memory to realize the reading and modification of the

);ParametersADDR: the starting address to be mapped. It is usually specified as null to allow the kernel to automatically selectLen: number of bytes mapped to the process address spaceProt: ing protection modeFlags: FlagFD: file descriptorOffset: the offset starting from the file header, which must be an integer multiple of the page size (generally 4 K in 32-bit system structure)Returned value: the start a

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

Recently, the instructor said this: MMAP () memory ing can be used to copy files, and the speed is significantly faster than normal file copying.I tried to copy two files at a time.First, check the Code: # Include # Include# Include # Include# Include # Include# Include # Include # Include# Include # DefineBuffer_size 1 Void my_copy1 (){Int fin, fout;Void * start;Void * end;Struct stat Sb;If (fin =Open ("

You can't simply say which method is highly efficient. Either method is nothing more than the OS that helps you cache your memory, and then the fl at some point in time. To the memory. MMAP can easily simplify file operations and is more efficient than Directly Reading and Writing files. Introduced a few paragraphs: "This problem is complicated and it cannot be simply said that

From: http://blog.csdn.net/scorpio16/article/details/2059623 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 perfo

function, which is defined in mm/mmap. c. SYSCALL_DEFINE6 (mmap_pgoff, unsigned long, addr, unsigned long, len, Unsigned long, prot, unsigned long, flags, Unsigned long, fd, unsigned long, pgoff) { Struct file * file = NULL; Unsigned long retval =-EBADF; If (! (Flags MAP_ANONYMOUS) {/* anonymous ing */ Audit_mmap_fd (fd, flags ); If (unlikely (flags

(unsigned long addr, unsigned long len,unsigned long prot, unsigned long flags,unsigned long fd, unsigned long pgoff); 6) sys_mmap_pgoff implementationThe implementation in kernel/MM/MMAP. C is as follows: SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr, unsigned long, len,unsigned long, prot, unsigned long, flags,unsigned long, fd, unsigned long, pgoff){struct file *fi