I have an additional query in the same situation. I was reading the 'Linux kernel module programming 2.6'. For a simple char device driver, the sample code was using 'sprintf' routine to copy the a message from kernel space to user space. I want to know is this valid. If so, then how is the snprintf routine working? Is it a kernel Provided routine also? IF not valid, then how is that when i tried that code, it worked.
Thanks in advance
sandeep
On 1/28/06, Gaurav Dhiman <gauravd.chd@xxxxxxxxx> wrote:
On 1/27/06, Medeiros Edward M NPRI <MedeirosEM@xxxxxxxxxxxxxxxxx > wrote:
>
>
>
> 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);
>
check the user buffer before passing it to system call, it might be
NULL id malloc is unable to allocate memory. If you pass invaliduser
address copy_to_user will make the kernel panic.
-Gaurav
> 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.
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