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memory addressing
by 慕冬亮 May 20, 2015

May 20, 2015

In Understanding the Linux kernel book, it says that linux kernel of x86 uses the segmentation and paging unit to transform logistic address to physical address! Up to now , kernel has gone to linux kernel 4.0 , does the segmentation exist in the x86? Is it only using the paging ? And in x86_64?

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device returned IRQ_WAKE_THREAD but no thread function avable error
by Chan Kim May 20, 2015

May 20, 2015

In the smsc911x Ethernet chip driver, I'm changing the FIFO write and read to DMA write and read. By the way, this driver uses loopback test during initialization using a simple test packet. I registered the DMA controller irq using request_irq(irq, handler, flags, name, dev) which calls request_threaded_irq(irq, handler, NULL, flags, name, dev). The process goes into sleep using wait_event_interruptible() after DMA command and I've seen the ISR handler is called by the DMA completion, and during the ISR, wake_up_interruptible() is called to wake up the process. But when the program runs I get this error message below during the first interrupt processing. "IRQ 2 device ald_dmac returned IRQ_WAKE_THREAD but no thread function available" I don't know why ald_dmac returned IRQ_WAKE_THREAD (because my interrupt handler only returns IRQ_HANDLED), and I have a feeling that in this case (processing going to sleep and woken up by the ISR), I should use some other method to register my interrupt. Can anybody give me some advice? Thanks a lot in advance. Chan Kim

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A flow path for ethernet kernel driver
by Airton Ishimori May 19, 2015

May 19, 2015

Hello, everybody, I'm trying to develop a new Ethernet driver (Realtek) for Linux kernel 4.0.2. [ 3.612938] r8169 Gigabit Ethernet driver 2.3LK-NAPI loaded As part of my studies, I'm trying to trace the path for functions defined in drivers/net/ethernet/realtek/r8169.c, net/core/dev.c and net/core/dev_ioctl.c. I'm using "printks" for this purpose. For instance, something like: printk("TEST: __dev_set_promiscuity\n"); However, I'm not getting what's going on. I can set/unset the promiscuity behaviour via ifconfig command. [ 131.330091] device eth0 entered promiscuous mode [ 170.619086] device eth0 left promiscuous mode By looking at the dmesg output above, I thought the function that deals with promiscuity was __dev_set_promiscuity() defined in net/core/dev.c, because this function calls a function to print the message above: pr_info("device %s %s promiscuous mode\n", dev->name, dev->flags & IFF_PROMISC ? "entered" : "left"); But, when I tried to look for my printk message with dmesg after compiling and running the kernel, I couldn't find it. $ cd linux-4.0.2/ $ make net && make modules $ sudo make modules_install && sudo make install Can somebody help me to understand what's happening? Thanks in advance, *--*Airton Ishimori

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Question about struct block_device
by Rock Lee May 19, 2015

May 19, 2015

Hello: In struct block_device, there are two counters, one is bd_openers, and the other is bd_part_count. Why do there need those two counters? Can anybody give me some hint? -- Rock Lee

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Re: Addning new protocol and new driver on Linux
by Daniel. May 18, 2015

May 18, 2015

A new topic to the list :) - Write netlink api for access with iproute2 Cheers, 2015-05-18 17:21 GMT-03:00 Daniel. <danielhilst(a)gmail.com>: > Hi all! > > I have a driver for nordic nRF24L01+ module: > http://www.nordicsemi.com/eng/Products/2.4GHz-RF/nRF24L01P > > I'm looking for a requirements list of what I need to do. For now I have > this topics > > - Write driver using kernel NAPI (I already have a driver working with > cdev API) > - Write new protocol and export to userspace as a new socket type (no > ideia on this) > > As example I'm using the linux socketCan, I want to do like they did, but > with nRF24L01+. I have no ideia how this two topics touch one each other... > Any documentation, simple examples, tutorials, guide lines, articles or irc > chat on subject is welcome, I look on LDD3, but its outdated, I'm using > kernel 3.0 for development, > > As first version requeriment I want to send frames (32 bytes fixed) with > sendto() and receive (32 bytes fixed too) with recvfrom()... Messages > should be enqueued while sending, the driver need to iterate over a > circular list of remote nodes, exchaning frames and delivering the received > to userspace... > > Something like: > > for (;;) { > node *n = get_next_node(); > send_frames_to(n); // <- send enqueed frames, unblocking sendto() caller > receive_frames_from(n); // <- deliver received frames to recvfrom() > caller > } > > Thanks in advance! > Cheers > > -- > *"Do or do not. There is no try"* > *Yoda Master* > -- *"Do or do not. There is no try"* *Yoda Master*

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Addning new protocol and new driver on Linux
by Daniel. May 18, 2015

May 18, 2015

Hi all! I have a driver for nordic nRF24L01+ module: http://www.nordicsemi.com/eng/Products/2.4GHz-RF/nRF24L01P I'm looking for a requirements list of what I need to do. For now I have this topics - Write driver using kernel NAPI (I already have a driver working with cdev API) - Write new protocol and export to userspace as a new socket type (no ideia on this) As example I'm using the linux socketCan, I want to do like they did, but with nRF24L01+. I have no ideia how this two topics touch one each other... Any documentation, simple examples, tutorials, guide lines, articles or irc chat on subject is welcome, I look on LDD3, but its outdated, I'm using kernel 3.0 for development, As first version requeriment I want to send frames (32 bytes fixed) with sendto() and receive (32 bytes fixed too) with recvfrom()... Messages should be enqueued while sending, the driver need to iterate over a circular list of remote nodes, exchaning frames and delivering the received to userspace... Something like: for (;;) { node *n = get_next_node(); send_frames_to(n); // <- send enqueed frames, unblocking sendto() caller receive_frames_from(n); // <- deliver received frames to recvfrom() caller } Thanks in advance! Cheers -- *"Do or do not. There is no try"* *Yoda Master*

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Linux 14.04 stuck at "Loading initial RAM disk"
by Ramesh May 18, 2015

May 18, 2015

Hi All, I have linux 14.04 with 64-bit kernel and recently I installed 32 bit kernel in my machine. After installation complete I restarted machine to login to new 32 bit kernel. But when I try to logging in to the newly installed 32 bit kernel system get stuck in "Loading initial RAM disk" Please someone help me Thanks in advance... -- Regards, Ramesh

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vulnerability use-after-free
by 慕冬亮 May 17, 2015

May 17, 2015

Use-after-free is a important vulnerability ! As far as we know , Linux kernel is mostly using C and there may exist this vulnerability! I think in the kernel there are much allocator and reallocator , how do the kernel manage these things? mudongliang

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linux timer questions
by buyitian May 17, 2015

May 17, 2015

Dear Experts: I have some questions about the linux timers: Dear Experts: I have some questions about the linux timers: 1. If one linux platform does not enable CONFIG_HIGH_RES_TIMERS, it means the platform does not support high resulution timer, what is the side effect? Is there any exact examples that can let me know the necessary of hrtimer? For example, if hrtimer is not enabled in code, the video 1080P will not work? I need these kind of examples to judge whether to enable hrtimer. Dear Experts: I have some questions about the linux timers: 1. Suppose in one linux platform, the timer HW is far from CPU core, if CPU wants to access timer register, it needs to go through several bus(AXI, AHB, APB), finally the access arrives at timer register, in this example, if I enable CONFIG_TICK_ONESHOT, and if the HZ == 512, it means CPU core needs to call function set_next_event 512 times per second, and the access latency caused by HW design will be large, how to mitigate this? Dear Experts: I have some questions about the linux timers: 1. Suppose in one linux platform, the system counter HW is far from CPU core, if CPU wants to access system counter, it needs to go though several bus(AXI, AHB, APB), fianally the access arrives at counter register, as far as I know, kernel will call update_wall_time based on HZ, suppose HZ == 512, it means the update_wall_time will be called 512 times per second. And inside function update_wall_time, it will read system counter register. So the access latency caused by system counter HW design will be large, how to mitigate this? Thanks in advance.

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x86 driver help: ever see DMA and MMIO operations NMI depending on which PCIe slot you're installed in?
by Jimmie Mayfield May 17, 2015

May 17, 2015

Hi all. We're in the midst of performing system compatibility tests with our device and I'm seeing some odd behavior when testing a Lenovo x3650 M4 and M5 machines. 1) On the x3650 M4 machine, an attempt to perform a TODEVICE DMA operation using consistent memory results in an NMI when the device attempts to fetch the memory. Here's the thing: this NMI only happens when the device is plugged into certain PCIe slots. Some slots appear to work fine. We obtained PCIe bus analyzer traces for the NMI scenario and sent to Lenovo for analysis. Their response was a rather terse "memory address is invalid". We later obtained an analyzer trace for a non-NMI scenario in a different slot and saw the very same bus address. So I'm very confused: is it possible for a bus address allocated via pci_alloc_consistent to be valid only for specific PCIe slots? Shouldn't the kernel be able to allocate valid memory since it's given the pci_dev * as an argument? 2) On the x3650 M5 machine, an attempt to perform MMIO operations results in an NMI. Again, only from certain slots. Some slots seem to work fine. Again, near as I can tell, the slots are physically the same -- same width, same power capabilities, etc. Again, we obtained PCIe bus analyzer traces for both the NMI and the non-NMI scenarios and compared. There's a lot of noise in the traces because the machine BIOS appears to poll the PCI registers repeatedly and frequently but once the driver enables the device, we don't see anything that stands out in one case or the other. In both traces, we see the device receive the MMIO read request and respond about a microsecond later. In the NMI trace, the NMI occurs after the device writes the MMIO response. So I'm scratching my head. Has anyone seen such slot-specific behavior? How does one account for this in a device driver?

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