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lemonsqueezelemonsqueeze
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naive /dev/mem mmap() experiment
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4 files changed

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‎.gitignore‎

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*~
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*.o
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*.ko
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*.cmd
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*.order
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*.mod.c
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*.symvers
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.tmp_versions

‎hello.c‎

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@@ -12,6 +12,8 @@
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#include <linux/init.h> // Macros used to mark up functions e.g., __init __exit
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#include <linux/module.h> // Core header for loading LKMs into the kernel
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#include <linux/kernel.h> // Contains types, macros, functions for the kernel
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#include <linux/page-flags.h>
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#include <asm/cacheflush.h>
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MODULE_LICENSE("GPL"); ///< The license type -- this affects runtime behavior
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MODULE_AUTHOR("Derek Molloy"); ///< The author -- visible when you use modinfo
@@ -22,6 +24,63 @@ static char *name = "world"; ///< An example LKM argument -- default valu
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module_param(name, charp, S_IRUGO); ///< Param desc. charp = char ptr, S_IRUGO can be read/not changed
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MODULE_PARM_DESC(name, "The name to display in /var/log/kern.log"); ///< parameter description
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#if 0
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// x86 only ?
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#define alloc_gatt_pages(order) \
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((char *)__get_free_pages(GFP_KERNEL, (order)))
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#define free_gatt_pages(table, order) \
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free_pages((unsigned long)(table), (order))
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#endif
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// use vmalloc()
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static int page_order = 10; // we allocate (1<<page_order) pages
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static char *table = 0;
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static void
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hello_alloc_pages(void)
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{
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struct page *page;
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char *table_end;
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table = (char*) __get_free_pages(GFP_KERNEL, page_order);
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if (!table) { printk(KERN_WARNING "Could not allocate pages\n"); return; }
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printk(KERN_WARNING "sizeof(phys_addr_t): %i\n", sizeof(phys_addr_t));
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if (sizeof(phys_addr_t) == 8)
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printk(KERN_WARNING "Allocated %li bytes (%i pages) at 0x%llx\n",
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(1 << page_order) * PAGE_SIZE, 1 << page_order, virt_to_phys(table));
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table_end = table + ((PAGE_SIZE * (1 << page_order)) - 1);
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for (page = virt_to_page(table); page <= virt_to_page(table_end); page++)
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SetPageReserved(page);
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*((int*)table) = 0xdeadbeaf;
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if (set_memory_uc((unsigned long)table, 1 << page_order))
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printk(KERN_WARNING "Could not set pages to UC!\n");
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else
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printk(KERN_WARNING "Success !\n");
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}
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static void
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hello_free_pages(void)
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{
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char *table_end = table + ((PAGE_SIZE * (1 << page_order)) - 1);
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struct page *page;
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printk(KERN_WARNING "Freeing pages\n");
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set_memory_wb((unsigned long)table, 1 << page_order);
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for (page = virt_to_page(table); page <= virt_to_page(table_end); page++)
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ClearPageReserved(page);
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free_pages((unsigned long)(table), (page_order));
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}
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/** @brief The LKM initialization function
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* The static keyword restricts the visibility of the function to within this C file. The __init
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* macro means that for a built-in driver (not a LKM) the function is only used at initialization
@@ -30,6 +89,7 @@ MODULE_PARM_DESC(name, "The name to display in /var/log/kern.log"); ///< parame
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*/
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static int __init helloBBB_init(void){
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printk(KERN_INFO "EBB: Hello %s from the BBB LKM!\n", name);
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hello_alloc_pages();
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return 0;
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}
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@@ -38,6 +98,8 @@ static int __init helloBBB_init(void){
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* code is used for a built-in driver (not a LKM) that this function is not required.
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*/
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static void __exit helloBBB_exit(void){
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if (table)
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hello_free_pages();
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printk(KERN_INFO "EBB: Goodbye %s from the BBB LKM!\n", name);
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}
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‎test/Makefile‎

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CC=gcc
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#CFLAGS=-Wall -ggdb3 -std=gnu99 -O3
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CFLAGS=-Wall -ggdb3 -std=gnu99
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all: test
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clean:
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-@ rm test *~ >/dev/null 2>&1
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‎test/test.c‎

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#include <stdlib.h>
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#include <stdio.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <sys/mman.h>
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#include <sys/time.h>
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#include <string.h>
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#include <assert.h>
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void usage(int ac, char **av)
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{
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printf("usage: %s cached addr\n", av[0]);
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printf(" %s uncached addr\n", av[0]);
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exit(1);
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}
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void die(char *msg)
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{
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printf("%s\n", msg);
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exit(1);
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}
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/* Returns the current time. */
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double time_now(void)
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{
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#if _POSIX_TIMERS > 0
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struct timespec now;
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clock_gettime(CLOCK_REALTIME, &now);
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return now.tv_sec + now.tv_nsec/1000000000.0;
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#else
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struct timeval now;
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gettimeofday(&now, NULL);
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return now.tv_sec + now.tv_usec/1000000.0;
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#endif
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}
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void *get_uncached_mem(void *base_addr, int size)
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{
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int fd = open("/dev/mem", O_RDWR | O_SYNC, 0);
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if (fd == -1) die("couldn't open /dev/mem, are you root ?");
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printf("mmap()'ing %p\n", base_addr);
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void *map = mmap(0, size, PROT_READ /*| PROT_WRITE*/, MAP_FILE | MAP_SHARED, fd, (off_t)base_addr);
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if (map == MAP_FAILED)
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die("mmap failed. Note: we need a kernel without CONFIG_STRICT_DEVMEM.");
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return map;
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}
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int main(int ac, char **av)
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{
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int size = 1024 * 4096; // FIXME
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if (ac != 3)
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usage(ac, av);
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int uncached_mem_test;
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if (!strcmp(av[1], "uncached")) uncached_mem_test = 1;
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else if (!strcmp(av[1], "cached")) uncached_mem_test = 0;
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else usage(ac, av);
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void *base_addr = (void*)strtoul(av[2], NULL, 16);
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void *map;
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if (uncached_mem_test)
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map = get_uncached_mem(base_addr, size);
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else
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map = malloc(size); /* test normal memory */
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unsigned int *pt = ((unsigned int*)map);
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/* uncached mem should start with 0xdeadbeaf */
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printf("read %#0x\n", *pt);
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if (uncached_mem_test) assert(*pt == 0xdeadbeaf);
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//printf("sizeof(off_t): %i\n", sizeof(off_t));
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/*********************************************************************/
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/* benchmark reads */
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double time_start = time_now();
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int tsize = size / sizeof(int);
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//int t[tsize];
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#define STEP 10
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unsigned int sum = 0;
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int reads = 0;
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for (int i = 0; i < tsize - STEP; i++)
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for (int j = 0; j < STEP; j++) {
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sum += pt[i+j];
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reads++;
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}
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printf("%s mem test: %i reads in %.2fs (sum: %i)\n",
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(uncached_mem_test ? "uncached" : "cached"),
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reads, time_now() - time_start, sum);
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}

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