linux-device-driver

问题 I want to use my DSLR camera as video input for let say Skype / Google talk under Linux and Android. Is it possible to create a video loop back using v4l2loopback and Canon EDSDK ? how can I pipe the liveview buffer from the camera to the video loop back ? Thanks 回答1: you will need a "producer" application, that writes frames to the loopback device (and which has previously acquired those frames via the canon esdk) v4l2loopback already comes with a few simple producer examples, and you could

问题 Working on a Linux PCI driver, now I'm trying to write codes for DMA using scatter/gather. For now, I've learned that to access to DMA datas directly from User space, we need to pin user space pages to kernel space. And to do this, we have get_user_pages , its full definition is like: int get_user_pages(struct task_struct * tsk, struct mm_struct * mm, unsigned long start, int nr_pages, int write, int force, struct page ** pages, struct vm_area_struct ** vmas); My first question is about the

问题 It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center. Closed 8 years ago . How to get signal from kernel space to user space? 回答1: To get the signal from kernel to user space use the following code in your user space and kernel space code as below : user space application : signal(SIGIO

问题 I understand that in Linux the mm_struct describes the memory layout of a process. I also understand that the start_brk and brk mark the start and end of the heap section of a process respectively. Now, this is my problem: I have a process, for which I wrote the source code, that allocates 5.25 GB of heap memory using malloc . However, when I examine the process's mm_sruct using a kernel module I find the value of is equal to 135168. And this is different from what I expected: I expected brk

问题 As we all know, in the CAN bus communication protocol, sender know whether the data was successfully sent. I send socketcan data as follows. ret = write (socket, frame, sizeof (struct can_frame)); However, even if the CAN communication cable is disconnected, the return value of ret is still 16(=sizeof (struct can_frame)).I queried the information and found that the problem was due to the tx_queue of the network stack used by socketcan. When write is called multiple times, the buffer is full

问题 in r8169 driver from realtek it does rx_buf = page_address(tp->Rx_databuff[entry]); dma_sync_single_for_cpu(d, addr, pkt_size, DMA_FROM_DEVICE); prefetch(rx_buf); skb_copy_to_linear_data(skb, rx_buf, pkt_size);<----//Do I get packet at this???? skb->tail += pkt_size; skb->len = pkt_size; dma_sync_single_for_device(d, addr, pkt_size, DMA_FROM_DEVICE); //csum... skb->protocol = eth_type_trans(skb, dev); napi_gro_receive(&tp->napi, skb); this is inside rtl_rx function called from poll of driver.

问题 in r8169 driver from realtek it does rx_buf = page_address(tp->Rx_databuff[entry]); dma_sync_single_for_cpu(d, addr, pkt_size, DMA_FROM_DEVICE); prefetch(rx_buf); skb_copy_to_linear_data(skb, rx_buf, pkt_size);<----//Do I get packet at this???? skb->tail += pkt_size; skb->len = pkt_size; dma_sync_single_for_device(d, addr, pkt_size, DMA_FROM_DEVICE); //csum... skb->protocol = eth_type_trans(skb, dev); napi_gro_receive(&tp->napi, skb); this is inside rtl_rx function called from poll of driver.

问题 As I was going through the Interrupt Handling in Linux, I had this question if we can make reference to the current macro pointing to the interrupted task, while the core is in hard-irq mode? Also, if this referencing is possible whatwill happen if we make a call to semaphore "down", though this is highly discouraged.? 回答1: I believe it's possible to do, at least on x86, in the sense that it won't cause an immediate panic. It is however ALWAYS wrong to do this. An interrupt is not associated

问题 As I was going through the Interrupt Handling in Linux, I had this question if we can make reference to the current macro pointing to the interrupted task, while the core is in hard-irq mode? Also, if this referencing is possible whatwill happen if we make a call to semaphore "down", though this is highly discouraged.? 回答1: I believe it's possible to do, at least on x86, in the sense that it won't cause an immediate panic. It is however ALWAYS wrong to do this. An interrupt is not associated

问题 I am trying to rescan PCI bus in my own kernel driver with the help of pci_rescan_bus() kernel function but I do not see it is functioning same. If I try to do same from user space by running following command, I see that rescanning happens: echo 1 > /sys/devices/pci0000:00/0000:00:14.1/rescan I am trying to re-initialize my ethernet ports which sit on PCI bus. Below is the code I am using for now: struct pci_dev *pci_eth_dev01, *pci_eth_dev02 = NULL; pci_eth_dev01 = pci_get_device(0x10ec,