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      1 // SPDX-License-Identifier: GPL-2.0
      2 /*
      3  * hugepage-mmap:
      4  *
      5  * Example of using huge page memory in a user application using the mmap
      6  * system call.  Before running this application, make sure that the
      7  * administrator has mounted the hugetlbfs filesystem (on some directory
      8  * like /mnt) using the command mount -t hugetlbfs nodev /mnt. In this
      9  * example, the app is requesting memory of size 256MB that is backed by
     10  * huge pages.
     11  *
     12  * For the ia64 architecture, the Linux kernel reserves Region number 4 for
     13  * huge pages.  That means that if one requires a fixed address, a huge page
     14  * aligned address starting with 0x800000... will be required.  If a fixed
     15  * address is not required, the kernel will select an address in the proper
     16  * range.
     17  * Other architectures, such as ppc64, i386 or x86_64 are not so constrained.
     18  */
     19 
     20 #include <stdlib.h>
     21 #include <stdio.h>
     22 #include <unistd.h>
     23 #include <sys/mman.h>
     24 #include <fcntl.h>
     25 
     26 #define FILE_NAME "huge/hugepagefile"
     27 #define LENGTH (256UL*1024*1024)
     28 #define PROTECTION (PROT_READ | PROT_WRITE)
     29 
     30 /* Only ia64 requires this */
     31 #ifdef __ia64__
     32 #define ADDR (void *)(0x8000000000000000UL)
     33 #define FLAGS (MAP_SHARED | MAP_FIXED)
     34 #else
     35 #define ADDR (void *)(0x0UL)
     36 #define FLAGS (MAP_SHARED)
     37 #endif
     38 
     39 static void check_bytes(char *addr)
     40 {
     41 	printf("First hex is %x\n", *((unsigned int *)addr));
     42 }
     43 
     44 static void write_bytes(char *addr)
     45 {
     46 	unsigned long i;
     47 
     48 	for (i = 0; i < LENGTH; i++)
     49 		*(addr + i) = (char)i;
     50 }
     51 
     52 static int read_bytes(char *addr)
     53 {
     54 	unsigned long i;
     55 
     56 	check_bytes(addr);
     57 	for (i = 0; i < LENGTH; i++)
     58 		if (*(addr + i) != (char)i) {
     59 			printf("Mismatch at %lu\n", i);
     60 			return 1;
     61 		}
     62 	return 0;
     63 }
     64 
     65 int main(void)
     66 {
     67 	void *addr;
     68 	int fd, ret;
     69 
     70 	fd = open(FILE_NAME, O_CREAT | O_RDWR, 0755);
     71 	if (fd < 0) {
     72 		perror("Open failed");
     73 		exit(1);
     74 	}
     75 
     76 	addr = mmap(ADDR, LENGTH, PROTECTION, FLAGS, fd, 0);
     77 	if (addr == MAP_FAILED) {
     78 		perror("mmap");
     79 		unlink(FILE_NAME);
     80 		exit(1);
     81 	}
     82 
     83 	printf("Returned address is %p\n", addr);
     84 	check_bytes(addr);
     85 	write_bytes(addr);
     86 	ret = read_bytes(addr);
     87 
     88 	munmap(addr, LENGTH);
     89 	close(fd);
     90 	unlink(FILE_NAME);
     91 
     92 	return ret;
     93 }
     94