常用的連續實體記憶體的獲取方法(一)
獲得連續實體記憶體的方法有很多,在很多地方搜了但是自己拿過來用就是用不了,這裡展示幾個親測能用的。包括dma_alloc_coherent和kmalloc等。
程式碼:
效果:#include <linux/module.h> #include <linux/init.h> #include <linux/pci.h> #include <linux/slab.h> #include <linux/dma-mapping.h> #include <linux/dmapool.h> #include <linux/device.h> // int direction = PCI_DMA_TODEVICE ; // int direction = PCI_DMA_FROMDEVICE ; static int direction = PCI_DMA_BIDIRECTIONAL; //int direction = PCI_DMA_NONE; static char *kbuf; static dma_addr_t handle; static size_t size = (10 * PAGE_SIZE); static struct dma_pool *mypool; static size_t pool_size = 1024; static size_t pool_align = 8; static void my_release(struct device *dev) { pr_info("releasing DMA device\n"); } static struct device dev = { .release = my_release }; static void output(char *kbuf, dma_addr_t handle, size_t size, char *string) { unsigned long diff; diff = (unsigned long)kbuf - handle; pr_info("kbuf=%12p, handle=%12p, size = %d\n", kbuf, (unsigned long *)handle, (int)size); pr_info("(kbuf-handle)= %12p, %12lu, PAGE_OFFSET=%12lu, compare=%lu\n", (void *)diff, diff, PAGE_OFFSET, diff - PAGE_OFFSET); strcpy(kbuf, string); pr_info("string written was, %s\n", kbuf); } static int __init my_init(void) { dev_set_name(&dev, "my0"); device_register(&dev); /* dma_alloc_coherent method */ pr_info("Loading DMA allocation test module\n"); pr_info("\nTesting dma_alloc_coherent()..........\n\n"); kbuf = dma_alloc_coherent(NULL, size, &handle, GFP_KERNEL); output(kbuf, handle, size, "This is the dma_alloc_coherent() string"); dma_free_coherent(NULL, size, kbuf, handle); /* dma_map/unmap_single */ pr_info("\nTesting dma_map_single()................\n\n"); kbuf = kmalloc(size, GFP_KERNEL); handle = dma_map_single(NULL, kbuf, size, direction); output(kbuf, handle, size, "This is the dma_map_single() string"); dma_unmap_single(NULL, handle, size, direction); kfree(kbuf); /* dma_pool method */ /* pr_info("\nTesting dma_pool_alloc()..........\n\n"); mypool = dma_pool_create("mypool", NULL, pool_size, pool_align, 0); kbuf = dma_pool_alloc(mypool, GFP_KERNEL, &handle); output(kbuf, handle, size, "This is the dma_pool_alloc() string"); dma_pool_free(mypool, kbuf, handle); dma_pool_destroy(mypool); */ device_unregister(&dev); return 0; } static void __exit my_exit(void) { pr_info("Module Unloading\n"); } module_init(my_init); module_exit(my_exit); MODULE_AUTHOR("Jerry Cooperstein"); MODULE_DESCRIPTION("LDD:2.0 s_23/lab1_dma.c"); MODULE_LICENSE("GPL v2");
[ 5689.589449] Loading DMA allocation test module
[ 5689.589450]
Testing dma_alloc_coherent()..........
[ 5689.589463] kbuf=ffff8e8b42240000, handle= 2240000, size = 40960
[ 5689.589464] (kbuf-handle)= ffff8e8b40000000, 18446619327458181120, PAGE_OFFSET=18446619327458181120, compare=0
[ 5689.589464] string written was, This is the dma_alloc_coherent() string
[ 5689.589465]
Testing dma_map_single()................
[ 5689.589466] kbuf=ffff8e8b42240000, handle= 2240000, size = 40960
[ 5689.589466] (kbuf-handle)= ffff8e8b40000000, 18446619327458181120, PAGE_OFFSET=18446619327458181120, compare=0
[ 5689.589467] string written was, This is the dma_map_single() string
[ 5689.589492] releasing DMA device
環境:Linux ubuntu 4.13.0-26-generic
不足之處是dma_pool method沒有實現,夥伴們可自行實踐然後一起交流哦。