November 2016 - kernelnewbies@kernelnewbies.org

Understanding Platform devices and platform drivers.
by Madhu K Nov. 7, 2016

Nov. 7, 2016

Hi All, I am trying to understand the concept of platform device and platform driver, my very basic question is that, the devices and data which is present in device tree represents platform devices and platform data? Regards, Madhu

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The sequence of the built in kernel module be probed
by Hao Zhang Nov. 7, 2016

Nov. 7, 2016

hi, what's the sequence of the built in kernel module be probed? and how to change it ?

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PCI drivers and interrupts
by Kenneth Adam Miller Nov. 4, 2016

Nov. 4, 2016

Hello, I'm trying to author a driver that communicates over shared memory within the kernel land between concurrent userland processes. I'm using this as a base: https://github.com/henning-schild/ivshmem-guest-code/blob/master/kernel_mod… I've been able to build it and to insmod it into a linux that I have built and started running in qemu. I need a way to send an interrupt, as per the documentation mentions in the device_spec and in the guide. But I'm looking in the uio_ivshmem driver and I don't see functionality that corresponds to sending an interrupt at all. This functionality is supposed to be demonstrated in https://github.com/henning-schild/ivshmem-guest-code/tree/master/tests/Inte…, but this is problematic because it seems to indicate that one of the ioctls corresponds to an interrupt. Unless there's something I'm missing, I think that the stub pci driver implementation that this particular demo filled out implements some kind of interrupt, or else it's actually implemented with one of the function calls on line 28 or 43. But those each seem to correspond to interrupt handlers for receiving from other QEMU instances, with no sign of how they are *sent*. I need to write a function in the context of the driver that can be compiled in the same code, meaning editing uio_ivshmem.c and yielding some function interface like send_interrupt(int index), where index corresponds to the BAR against which the driver registers irq handlers anyway. How can I send interrupts from the kernel land using a particular BAR entry?

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zap_pid_ns_processes(struct pid_namespace)
by David Rodic Nov. 4, 2016

Nov. 4, 2016

Hi guys, I am reading "Linux Kernel Development". I came across the function call zap_pid_ns_processes(struct pid_namespace) inside the find_new_reaper function. Can someone tell me what this function does and why it is being called inside the find_new_reaper function? Thanks, David

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PMU suspend/resume
by Amit Mahadik Nov. 2, 2016

Nov. 2, 2016

Hi, I am trying to understand the Linux Power management Unit framework. I have an ARM Cortex-A9x4 board. When I enable pm_test or pass initcall_debug parameter through U-boot via bootargs the system goes into (wfi/suspend state) and resumes properly.However, the issue is when I disable pm_test and initcall_debug and put my system into WFI/SUSPEND state , it does not resume even if the registered wakeup IRQ is generated. I am using linux kernel source revision 4.4.16. Can somebody please help me regarding this issue? Regards,Amit.

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ip rule suppress_prefixlength
by Matthias Peter Walther Nov. 1, 2016

Nov. 1, 2016

Dear Linux-friends, I asked this question before on the netdev-Mailinglist, but never got an answer (Link: https://www.mail-archive.com/netdev@vger.kernel.org/msg133574.html) Maybe someone here can help me. I have a configuration like this: root@des1 ~ # ip rule 0: from all lookup local 32765: from all iif lo lookup ffnet suppress_prefixlength 0 32766: from all lookup main 32767: from all lookup default (ffnet is table 42) root@des1 ~ # ip r s default via 5.9.86.151 dev eth0 5.9.86.151 dev eth0 proto kernel scope link src 5.9.86.144 root@des1 ~ # ip r s t 42 blackhole default I have the default routing table, and a routing table number 42. I could use an ip rule filtering by destination ip, but I wanted to try suppress_prefixlength. Let's say I want to ping 8.8.8.8. What I expect is, that the package is put into routing table 42 by the ip rule 32765. As there is no more specific route for 8.8.8.8 than the default route in table 42, I expect the suppress_prefixlength 0 option to put it back to the default routing table and then to be send out through eth0. Instead this configuration takes the whole machine offline: root@des1 ~ # ping 8.8.8.8 connect: Invalid argument When I delete the ip rule 32765 containing the suppress_prefixlength, the machine is back online. Do I not understand the suppress_prefixlength-feature correctly or is this a bug? I tested with Kernel 4.7 and 4.6, both show the same behaviour as described above. Thanks for any replies in advance. Regards, Matthias

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