The mmap function is very important, alsa drives uac uvc audio and video and this entire application becomes a process, this function also plays a key role.
root@instance-tau7o2q5:~/app_modules# strace ./a.out . execve("./a.out", ["./a.out", "."], 0x7ffc78e587b8 /* 27 vars */) = 0 brk(NULL) = 0x559be8915000 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory) openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3 fstat(3, {st_mode=S_IFREG|0644, st_size=46616, ...}) = 0 mmap(NULL, 46616, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f4f4d50d000 close(3) = 0 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3 read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\260\34\2\0\0\0\0\0"..., 832) = 832 fstat(3, {st_mode=S_IFREG|0755, st_size=2030544, ...}) = 0 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f4f4d50b000 mmap(NULL, 4131552, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f4f4cf01000 mprotect(0x7f4f4d0e8000, 2097152, PROT_NONE) = 0 mmap(0x7f4f4d2e8000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1e7000) = 0x7f4f4d2e8000 mmap(0x7f4f4d2ee000, 15072, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f4f4d2ee000 close(3) = 0 arch_prctl(ARCH_SET_FS, 0x7f4f4d50c4c0) = 0 mprotect(0x7f4f4d2e8000, 16384, PROT_READ) = 0 mprotect(0x559be7d71000, 4096, PROT_READ) = 0 mprotect(0x7f4f4d519000, 4096, PROT_READ) = 0 munmap(0x7f4f4d50d000, 46616) = 0 openat(AT_FDCWD, "./file_mmap", O_RDWR|O_CREAT, 0600) = 3 fstat(3, {st_mode=S_IFREG|0644, st_size=294, ...}) = 0 mmap(NULL, 294, PROT_READ|PROT_WRITE, MAP_SHARED, 3, 0) = 0x7f4f4d518000 close(3) = 0 munmap(0x7f4f4d518000, 294) = 0 exit_group(0) = ? +++ exited with 0 +++
Did a file modification operation
#include <stdio.h> #include <string.h> #include <stdlib.h> #include <ctype.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <unistd.h> #include <sys/mman.h> struct Card_Messge { char number1; char number2; char number3; char number4; char number5; }; struct Card_Messge* Card ; int main(int argc, char *argv[]) { int fd; char *buf; off_t len; struct stat sb; char *fname = "./file_mmap"; fd = open(fname, O_RDWR | O_CREAT, S_IRUSR | S_IWUSR); if (fd == -1) { perror("open"); return 1; } if (fstat(fd, &sb) == -1) { perror("fstat"); return 1; } buf = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); if (buf == MAP_FAILED) { perror("mmap"); return 1; } Card = (struct Card_Messge*)buf; if (close(fd) == -1) { perror("close"); return 1; } for (len = 0; len < sb.st_size; ++len) { buf[len] = toupper(buf[len]); /*putchar(buf[len]);*/ } buf[0] = '1'; buf[1] = '2'; buf[2] = '3'; buf[3] = '4'; Card->number1 = 'a'; Card->number2 = 'b'; Card->number3 = 'c'; Card->number4 = 'd'; if (munmap(buf, sb.st_size) == -1) { perror("munmap"); return 1; } return 0;
