// SPDX-License-Identifier: GPL-2.0
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/*
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* hugepage-mmap:
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*
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* Example of using huge page memory in a user application using the mmap
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* system call. Before running this application, make sure that the
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* administrator has mounted the hugetlbfs filesystem (on some directory
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* like /mnt) using the command mount -t hugetlbfs nodev /mnt. In this
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* example, the app is requesting memory of size 256MB that is backed by
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* huge pages.
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*
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* For the ia64 architecture, the Linux kernel reserves Region number 4 for
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* huge pages. That means that if one requires a fixed address, a huge page
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* aligned address starting with 0x800000... will be required. If a fixed
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* address is not required, the kernel will select an address in the proper
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* range.
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* Other architectures, such as ppc64, i386 or x86_64 are not so constrained.
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*/
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#include <stdlib.h>
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#include <stdio.h>
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#include <unistd.h>
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#include <sys/mman.h>
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#include <fcntl.h>
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#define FILE_NAME "huge/hugepagefile"
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#define LENGTH (256UL*1024*1024)
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#define PROTECTION (PROT_READ | PROT_WRITE)
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/* Only ia64 requires this */
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#ifdef __ia64__
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#define ADDR (void *)(0x8000000000000000UL)
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#define FLAGS (MAP_SHARED | MAP_FIXED)
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#else
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#define ADDR (void *)(0x0UL)
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#define FLAGS (MAP_SHARED)
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#endif
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static void check_bytes(char *addr)
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{
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printf("First hex is %x\n", *((unsigned int *)addr));
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}
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static void write_bytes(char *addr)
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{
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unsigned long i;
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for (i = 0; i < LENGTH; i++)
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*(addr + i) = (char)i;
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}
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static int read_bytes(char *addr)
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{
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unsigned long i;
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check_bytes(addr);
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for (i = 0; i < LENGTH; i++)
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if (*(addr + i) != (char)i) {
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printf("Mismatch at %lu\n", i);
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return 1;
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}
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return 0;
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}
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int main(void)
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{
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void *addr;
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int fd, ret;
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fd = open(FILE_NAME, O_CREAT | O_RDWR, 0755);
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if (fd < 0) {
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perror("Open failed");
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exit(1);
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}
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addr = mmap(ADDR, LENGTH, PROTECTION, FLAGS, fd, 0);
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if (addr == MAP_FAILED) {
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perror("mmap");
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unlink(FILE_NAME);
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exit(1);
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}
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printf("Returned address is %p\n", addr);
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check_bytes(addr);
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write_bytes(addr);
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ret = read_bytes(addr);
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munmap(addr, LENGTH);
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close(fd);
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unlink(FILE_NAME);
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return ret;
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}
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