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Hello,
I have a basic "char" driver that controls a PCI device with DMA capability. I have a read routine that utilizes a "copy_to_user()" call to move data from a kernel-space buffer to a user-space buffer. The kernel space buffer was created by calling by "dma_alloc_coherent" as follows:
kernel_space_buffer_address = dma_alloc_coherent(&(pci_dev->dev), 1024*128, dma_handle_address, GFP_KERNEL);
I check that the "kernel_space_buffer_address" is not NULL and I print the address, which looks reasonable. Then later in my driver's read routine I have the following code:
static ssize_t pci_read(struct file *file, char __user *ubuffer, size_t length, loff_t *offset) {
bytes_read = copy_to_user((void __user *)ubuffer, (const void *)kernel_space_buffer_address), 10);
}
I have a simple user-space program that opens the device and calls the above read routine with:
main() { buffer = (char *)malloc(1024*8); fd = open("/dev/pci_drv", O_RDONLY); bytes_read = read(fd, buffer 10); close(fd); free(buffer); }
As soon as I hit the "read" I instantly get a kernel panic!!! Am I missing something with my use of "copy_to_user"??
Thank you for your time. |
