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I'm trying to write a small kernel module for TS-Linux ts-9 (Linux 2.4.26) on the TS-7200. All it should do is kmalloc a bit of memory and share it via mmap with a userland process. I've been trying lots of variations of code I've found on across the internet, but to no avail. I'm using remap_page_range in my kernel module's mmap function, which completes without error. However, trying to read/write to the mmap'ed buffer in userland does not work (always reads 0x0000 0000). I've also tried using get_free_page() instead of kmalloc and using nopage instead of remap_page_range to do the page table mapping. I've exhausted every attempt to fix this that I can think of. If you could take a look at my code and let me know if you see something wrong, please let me know. All of the source/Makefile/terminal spew is available at http://drop.io/woddjcp/asset/kmod-tar-gz. I'm also copying the terminal spew/code below. Thanks! -Mike Terminal Spew $ insmod accel_kmod.o Using accel_kmod.o Warning: loading accel_kmod will taint the kernel: no license See http://www.tux.org/lkml/#export-tainted for information about tainted modules init_module() Registration is a success. The major device number is 100. If you want to talk to the device driver, you'll have to create a device file. We suggest you use mknod accel_kmod c 100 0 The device file name is important, because the ioctl program assumes that's the file you'll use. virt_to_page(0xc4104000): 0xc00b2cb0 patterning memory dma buffer: kernel=0xc4104000, phys=0x04104000 $ ./accel_client device_open(c51411a0) device_mmap(0xc51411a0, 0xc1194b00) remap_page_range(0x2aac1000,0x04104000,4096,0x0000003F) dma_buf virt addr: 0x2aac1000 *** kernel mem stuff *** 0: 0x00000000 0x00000000 8: 0x00000000 0x00000000 16: 0x00000000 0x00000000 ... dma_buf[0]: 0x 0 *** writing 0xbeefbabe to kernel mem *** *** reading from kernel mem *** dma_buf[0]: 0xBEEFBABE device_release(c067da00,c51411a0) accel_kmod.c #define MODULE #define LINUX #define __KERNEL__ // We're doing kernel module work here. #include <linux/module.h> #include <linux/kernel.h> #include <linux/mm.h> // Deal with CONFIG_MODVERSIONS #if CONFIG_MODVERSIONS==1 #define MODVERSIONS #include <linux/modversions.h> #endif // Character device definitions are here #include <linux/fs.h> // A wrapper which does next to nothing // at the present, but may help for compatibility // with future versions of Linux. #include <linux/wrapper.h> // Our own IOCTL numbers #include "chardev.h" // For get_user and put_user #include <asm/uaccess.h> #define SUCCESS 0 // Pointer to unalgined data static int *dma_buf_ptr = NULL; // Pointer to page aligned area static int *dma_buf_area = NULL; // *** DEVICE DECLARATIONS **************************************************** // The name for our device (as it will appear in /proc/devices) #define DEVICE_NAME "accel_kmod" // Is the device open right now? (used to prevent concurrent access into the // same device) static int Device_Open = 0; // This function is called whenever a process attempts to open the device file static int device_open(struct inode *inode, struct file *file) { #ifdef DEBUG printk("device_open(%p)\n", file); #endif // DEBUG // We don't want to talk to two processes at the same time if (Device_Open) { return -EBUSY; } // If this was a process, we would have to be more careful here, because one // process might have checked Device_Open right before the other one tried // to increment it. However, we're in the kernel, so we're protected against // context switches. // // This is NOT the right attidue to take, because we might be running on an // SMP box, but we'll deal with SMP later if need be. Device_Open++; MOD_INC_USE_COUNT; return SUCCESS; } // This function is called when a process closes the device file. static int device_release(struct inode *inode, struct file *file) { #ifdef DEBUG printk("device_release(%p,%p)\n", inode, file); #endif // DEBUG // We're now ready for our next caller Device_Open--; MOD_DEC_USE_COUNT; return 0; } // *** Device memory map method *** // 2.4.x: this method is called from do_mmap_pgoff, from do_mmap, from the // syscall. The caller of do_mmap grabs the mm semaphore. So we are // protected from races here. int device_mmap(struct file *file, struct vm_area_struct *vma) { unsigned long offset = vma->vm_pgoff << PAGE_SHIFT; unsigned long size = vma->vm_end - vma->vm_start; printk("device_mmap(0x%p, 0x%p)\n", file, vma); if (offset & ~PAGE_MASK) { printk("offset not aligned: %ld\n", offset); return -ENXIO; } if (size > DMA_BUF_SIZE) { printk("size too big\n"); return -ENXIO; } // We only support shared mappings. Copy on write mappings are rejected here. // A shared mapping that is writeable must have the shared flag set. if ((vma->vm_flags & VM_WRITE) && !(vma->vm_flags & VM_SHARED)) { printk("writeable mappings must be shared, rejecting\n"); return -EINVAL; } // We do not want to have this area swapped out, lock it! vma->vm_flags |= VM_LOCKED | VM_RESERVED; // We create a mapping between the physical pages and the // virtual addresses of teh application with remap_page_range if (offset == 0) { printk("remap_page_range(0x%p,0x%p,%u,0x%08X)\n", vma->vm_start, (unsigned int)virt_to_phys(dma_buf_area), size, vma->vm_page_prot); if (remap_page_range(vma->vm_start, (unsigned int)virt_to_phys(dma_buf_area), size, vma->vm_page_prot)) { printk("remap page range failed\n"); return -ENXIO; } } else { printk("offset out of range\n"); return -ENXIO; } return SUCCESS; } // *** MODULE DECLARATIONS **************************************************** // This structure will hold the functions to be called when a process does // something to the device we created. Since a pointer to this structure is // kept in the devices table, it can't be local to init_module. NULL is for // unimplemented functions. struct file_operations Fops = { open: device_open, release: device_release, mmap: device_mmap }; // Initialize the module - register the character device int init_module() { int ret_val; unsigned int i; unsigned long dmaBuf_va; struct page *page; #ifdef DEBUG printk("init_module()\n"); #endif // DEBUG // Register the character device (at least try) ret_val = register_chrdev(MAJOR_NUM, DEVICE_NAME, &Fops); // Negative values signify an error if (ret_val < 0) { printk("Sorry, registering the character device failed with %d\n", ret_val); } printk("Registration is a success. The major device number is %d.\n", MAJOR_NUM); printk("If you want to talk to the device driver,\n" "you'll have to create a device file.\n" "We suggest you use mknod %s c %d 0\n", DEVICE_FILE_NAME, MAJOR_NUM); printk("The device file name is important, because\n" "the ioctl program assumes that's the\n" "file you'll use.\n\n"); // allocated DMA buffer in kernel memory // Align memory to a page - it will be physically contiguous dma_buf_ptr = (int *)kmalloc(DMA_BUF_SIZE+2*PAGE_SIZE, GFP_KERNEL | GFP_DMA); dma_buf_area = (int *)(((unsigned long)dma_buf_ptr + PAGE_SIZE - 1) & PAGE_MASK); for (dmaBuf_va = (unsigned long)dma_buf_area; dmaBuf_va < (unsigned long)dma_buf_area + DMA_BUF_SIZE; dmaBuf_va += PAGE_SIZE) { // reserve all pages to make them remapable printk("virt_to_page(0x%p): 0x%p\n", dmaBuf_va, virt_to_page(dmaBuf_va)); page = virt_to_page(dmaBuf_va); mem_map_reserve(page); } // Pattern the memory with some magic numbers (for testing!) printk("patterning memory\n"); for (i = 0; i < (DMA_BUF_SIZE/4); i += 2) { dma_buf_area[i] = (0xdead << 16) + i; dma_buf_area[i+1] = (0xbeef << 16) + i; } // Report alloc memory info! printk("dma buffer: kernel=0x%p, phys=0x%p\n", dma_buf_area, virt_to_phys(dma_buf_area)); return 0; } // Cleanup - unregister the appropriate file from /proc void cleanup_module() { #ifdef DEBUG printk("cleanup_module()\n"); #endif // DEBUG int ret; unsigned long va; // Unreserve all kmalloc'd pages for (va = (unsigned long)dma_buf_area; va < (unsigned long)dma_buf_area + DMA_BUF_SIZE; va += PAGE_SIZE) { mem_map_unreserve(virt_to_page(va)); } // Free kmallc'd pages if (NULL != dma_buf_area) { kfree((unsigned long)dma_buf_area); } // Unregister the device ret = unregister_chrdev(MAJOR_NUM, DEVICE_NAME); // If there's an error, report it if (ret < 0) { printk("Error in unregister_chrdev: %d\n", ret); } } chardev.h #ifndef CHARDEV_H #define CHARDEV_H #include <linux/ioctl.h> // The major device number. We can't rely on dynamic registration // because ioctls need to know it. #define MAJOR_NUM 100 // The name of the device file #define DEVICE_FILE_NAME "accel_kmod" #define DMA_BUF_SIZE 4096 #endif // CHARDEV_H accel_client.c #define MODULE #define LINUX #define __KERNEL__ // We're doing kernel module work here. #include <linux/module.h> #include <linux/kernel.h> #include <linux/mm.h> // Deal with CONFIG_MODVERSIONS #if CONFIG_MODVERSIONS==1 #define MODVERSIONS #include <linux/modversions.h> #endif // Character device definitions are here #include <linux/fs.h> // A wrapper which does next to nothing // at the present, but may help for compatibility // with future versions of Linux. #include <linux/wrapper.h> // Our own IOCTL numbers #include "chardev.h" // For get_user and put_user #include <asm/uaccess.h> #define SUCCESS 0 // Pointer to unalgined data static int *dma_buf_ptr = NULL; // Pointer to page aligned area static int *dma_buf_area = NULL; // *** DEVICE DECLARATIONS **************************************************** // The name for our device (as it will appear in /proc/devices) #define DEVICE_NAME "accel_kmod" // Is the device open right now? (used to prevent concurrent access into the // same device) static int Device_Open = 0; // This function is called whenever a process attempts to open the device file static int device_open(struct inode *inode, struct file *file) { #ifdef DEBUG printk("device_open(%p)\n", file); #endif // DEBUG // We don't want to talk to two processes at the same time if (Device_Open) { return -EBUSY; } // If this was a process, we would have to be more careful here, because one // process might have checked Device_Open right before the other one tried // to increment it. However, we're in the kernel, so we're protected against // context switches. // // This is NOT the right attidue to take, because we might be running on an // SMP box, but we'll deal with SMP later if need be. Device_Open++; MOD_INC_USE_COUNT; return SUCCESS; } // This function is called when a process closes the device file. static int device_release(struct inode *inode, struct file *file) { #ifdef DEBUG printk("device_release(%p,%p)\n", inode, file); #endif // DEBUG // We're now ready for our next caller Device_Open--; MOD_DEC_USE_COUNT; return 0; } // *** Device memory map method *** // 2.4.x: this method is called from do_mmap_pgoff, from do_mmap, from the // syscall. The caller of do_mmap grabs the mm semaphore. So we are // protected from races here. int device_mmap(struct file *file, struct vm_area_struct *vma) { unsigned long offset = vma->vm_pgoff << PAGE_SHIFT; unsigned long size = vma->vm_end - vma->vm_start; printk("device_mmap(0x%p, 0x%p)\n", file, vma); if (offset & ~PAGE_MASK) { printk("offset not aligned: %ld\n", offset); return -ENXIO; } if (size > DMA_BUF_SIZE) { printk("size too big\n"); return -ENXIO; } // We only support shared mappings. Copy on write mappings are rejected here. // A shared mapping that is writeable must have the shared flag set. if ((vma->vm_flags & VM_WRITE) && !(vma->vm_flags & VM_SHARED)) { printk("writeable mappings must be shared, rejecting\n"); return -EINVAL; } // We do not want to have this area swapped out, lock it! vma->vm_flags |= VM_LOCKED | VM_RESERVED; // We create a mapping between the physical pages and the // virtual addresses of teh application with remap_page_range if (offset == 0) { printk("remap_page_range(0x%p,0x%p,%u,0x%08X)\n", vma->vm_start, (unsigned int)virt_to_phys(dma_buf_area), size, vma->vm_page_prot); if (remap_page_range(vma->vm_start, (unsigned int)virt_to_phys(dma_buf_area), size, vma->vm_page_prot)) { printk("remap page range failed\n"); return -ENXIO; } } else { printk("offset out of range\n"); return -ENXIO; } return SUCCESS; } // *** MODULE DECLARATIONS **************************************************** // This structure will hold the functions to be called when a process does // something to the device we created. Since a pointer to this structure is // kept in the devices table, it can't be local to init_module. NULL is for // unimplemented functions. struct file_operations Fops = { open: device_open, release: device_release, mmap: device_mmap }; // Initialize the module - register the character device int init_module() { int ret_val; unsigned int i; unsigned long dmaBuf_va; struct page *page; #ifdef DEBUG printk("init_module()\n"); #endif // DEBUG // Register the character device (at least try) ret_val = register_chrdev(MAJOR_NUM, DEVICE_NAME, &Fops); // Negative values signify an error if (ret_val < 0) { printk("Sorry, registering the character device failed with %d\n", ret_val); } printk("Registration is a success. The major device number is %d.\n", MAJOR_NUM); printk("If you want to talk to the device driver,\n" "you'll have to create a device file.\n" "We suggest you use mknod %s c %d 0\n", DEVICE_FILE_NAME, MAJOR_NUM); printk("The device file name is important, because\n" "the ioctl program assumes that's the\n" "file you'll use.\n\n"); // allocated DMA buffer in kernel memory // Align memory to a page - it will be physically contiguous dma_buf_ptr = (int *)kmalloc(DMA_BUF_SIZE+2*PAGE_SIZE, GFP_KERNEL | GFP_DMA); dma_buf_area = (int *)(((unsigned long)dma_buf_ptr + PAGE_SIZE - 1) & PAGE_MASK); for (dmaBuf_va = (unsigned long)dma_buf_area; dmaBuf_va < (unsigned long)dma_buf_area + DMA_BUF_SIZE; dmaBuf_va += PAGE_SIZE) { // reserve all pages to make them remapable printk("virt_to_page(0x%p): 0x%p\n", dmaBuf_va, virt_to_page(dmaBuf_va)); page = virt_to_page(dmaBuf_va); mem_map_reserve(page); } // Pattern the memory with some magic numbers (for testing!) printk("patterning memory\n"); for (i = 0; i < (DMA_BUF_SIZE/4); i += 2) { dma_buf_area[i] = (0xdead << 16) + i; dma_buf_area[i+1] = (0xbeef << 16) + i; } // Report alloc memory info! printk("dma buffer: kernel=0x%p, phys=0x%p\n", dma_buf_area, virt_to_phys(dma_buf_area)); return 0; } // Cleanup - unregister the appropriate file from /proc void cleanup_module() { #ifdef DEBUG printk("cleanup_module()\n"); #endif // DEBUG int ret; unsigned long va; // Unreserve all kmalloc'd pages for (va = (unsigned long)dma_buf_area; va < (unsigned long)dma_buf_area + DMA_BUF_SIZE; va += PAGE_SIZE) { mem_map_unreserve(virt_to_page(va)); } // Free kmallc'd pages if (NULL != dma_buf_area) { kfree((unsigned long)dma_buf_area); } // Unregister the device ret = unregister_chrdev(MAJOR_NUM, DEVICE_NAME); // If there's an error, report it if (ret < 0) { printk("Error in unregister_chrdev: %d\n", ret); } } Makefile KMOD_TARGET := accel_kmod KMOD_CLIENT := accel_client INCLUDE := -isystem $(TS7200_KERNEL)/include WARN := -W CFLAGS := -O2 -DDEBUG $(WARN) $(INCLUDE) CC := arm-linux-gcc all: $(KMOD_TARGET).o $(KMOD_CLIENT) $(KMOD_TARGET).o: $(KMOD_TARGET).c $(KMOD_CLIENT): $(KMOD_CLIENT).c $(CC) -g -DDEBUG $(KMOD_CLIENT).c -o $(KMOD_CLIENT) .PHONY: clean clean: rm -rf $(KMOD_TARGET).o $(KMOD_CLIENT) deploy-kmod: scp -P 5022 accel_kmod.o :/kmod/ deploy-client: scp -P 5022 accel_client :/kmod/ deploy: all deploy-kmod deploy-client __._,_.___
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