mmap file

->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 this pointer to read and write the Gpio register, here is a bit of program snippet for everyone to refer

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

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 having to call read (), write (), and so on. The function prototypes are: #include void *mmap (void *addr, size_t length, int prot, int flags, int fd, off_t o

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

Comparison between MMAP and read/write on File Access We know that files accessed through MMAP or read/write must be cached in the kernel. When you need to read and write content from the file, the files are copied to the cache in the kernel for communication. 1. in read/write mode, the user must specify the number o

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 t

IPC Three communication mechanism refers to: semaphore, shared memory, message queue,signal Volume: Through the operating system of the PV operation to achieve;Shared Memory: Request a piece of memory, process A to write in shared memory, other processes can read out the contents of the shared memory to obtain the information transmitted by process A;Message Queuing: Create a message queue, process a writes to the queue, and process B gets the information that process a transmits by reading the

index, which means that index0 or index1 itself contains all the index information, setting two is only for expansion and reconstruction. In fact, the block part of the reader can be understood as a whole is a large block. The equivalent of index0 corresponding to the entire block, the index to rebuild the index information to switch to INDEX1, at this point, index1 corresponding blocks, the advantage of this is that only need to save a piece of data, and the index capacity expansion can be sep

" 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

Virtual space with remap_page_range, both the kernel and the user can access it. If the memory initialization string "ABCD" is added to the virtual address in the kernel, you can read it from the virtual address: /************ Mmap_ioremap.c **************/# Include # Include # Include # Include # Include # Include # Include Module_parm (mem_start, "I ");Module_parm (mem_size, "I ");Static int mem_start = 101, mem_size = 10;Static char * reserve_virt_addr;Static int Major;Int mmapdrv_o