mmap example

#作用: Create a memory-mapped file instead of reading the content directlyText message content: as follows (name is Text.txt)Lorem ipsum dolor sit amet, consectetuer adipiscing elit. DonecEgestas, enim et consectetuer ullamcorper, lectus ligula rutrum Leo,A elementum elit tortor EU quam.Duis tincidunt nisi ut ante. NullaFacilisi.Sed tristique eros eu libero. Pellentesque velArcu. Vivamus purus Orci, iaculis ac, suscipit sit amet, pulvinar EU,Lacus.Praesent placerat tortor sed nisl. Nunc blandit di

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

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 in the Mmap function.The principle is: the execution o

(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 process for shared memory modification is required, and map_fixed is not recommended for use.MUNMP () deletes the address mapping relationship, the function prototype is as follows: #inclu

/ * 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

Normal through the file system access to the value of Ain serial port, you can use Fread and other file IO read/sys/bus/iio/devices/iio:device0/in_voltage*_raw content. But this requires high frequency access to the ADC is very inefficient, the data needs to be copied from the disk to the kernel process space, and then copied to the user process space, consuming unnecessary resources. This problem can be solved by memory innuendo, Mmap can realize the

these. Let's look at one of the most commonly used write files Typical example, also the longest path of IO.{Char *buf = malloc (max_buf_size);strncpy (buf, SRC,, max_buf_size);Fwrite (BUF, max_buf_size, 1, FP);Fclose (FP);}The buf of malloc here is for application buffer in the layer, the application buffer, and after calling Fwrite, the data is copied from application buffer to the CLIB buffer, the C library standard Iobuffer. After Fwrite returns,

->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

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

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

650) this.width=650; "src="/img/fz.gif "alt=" Copy Code "style=" border:0px; "/>importmmapmmap_file=none# #从内存中读取信息, Defread_mmap_info (): globalmmap_filemmap_file.seek (0) ## Convert the binary to String info_str=mmap_file.read (). Translate (none,b ' \x00 '). Decode () print (INFO_STR) # #如果内存中没有对应信息, writes the information to memory for the next call to use Defget_mmap_info (): globalmmap_file# #第二个参数1024是设定的内存大小, units: bytes. If you have more content, you can turn it up a little bit mmap_f

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

Preface Work encountered some of the demand for KV storage, such as the recommendation system needs to store a commodity ID corresponding to the similar Product ID list, or a user's browsing the Product ID list, which requires a key value to store. This article describes the storage based on the requirements of a simple implementation of a version, the actual work is much more complex, in order to make the reader easy to understand, based on this analysis of a primary key to String key,value is

This article describes the POSIX environment uses file mapping IO method of operation, file mapping IO also known as storage mapping IO , for ordinary files, many times it is efficient, it actually reduces the duplication of data, and it can also be used in special places for communication between processes, a way of sharing memory. We can think of a file as a continuous piece of data, from a purely data point of view, which can be understood by any ordinary document. The file map actually corre

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 offset); Where the parameter addr is the descriptor FD should be mapped to the start address of the process space, when NULL is sp

); Mapfd (FD, size); // obtain a piece of memory by using the MMAP method of the FD. // Do not understand. Check man MMAP. After mapfd is complete, the mbase variable points to the starting position of the memory. msize indicates the size of the allocated memory, and MFD indicates File descriptor returned by ashmem_create_region } Memoryheapbase provides several functions to obtain the size and location o

Mmap function,1. mmap system call The man manual shows that: 1 void * mmap (void * addr, size_t length, int prot, int flags, 2 int fd, off_t offset ); Function: maps the file content to the virtual address space of the process. By reading and modifying the memory, you can read and modify the file without calling read and write; Parameters: Addr: Start addr

1. MmapMmap can map a portion of a disk file directly to memory, so that the location of the file directly has a corresponding memory address, read and write to the file can be directly with the pointer without the need for the Read/write function.Shared memory Exchange data, not switch the power level, fast.Mmap Cons: 1) consumes memory, fragmentation. 2) ordinary documents.Pros: 1) Map speed is fast. 2) can be atomic access to any byte, do not worry about offset.#include void *