December 2016 - kernelnewbies@kernelnewbies.org

Kernel boot panic
by Amit Mahadik Dec. 12, 2016

Dec. 12, 2016

Hi, I am trying to boot Linux kernel version 4.4.16 on custom ARM based development platform.I want to separate rootfs and kernel Image so that the size of my uImage is small. I followed the following steps. 1. Partitioned the SD card. It has 2 partition. First partition is formatted as vfat partition and has uImage (without rootfs). Second partition is formatted as ext3 and has the rootfs.2. I then changed the U-Boot (version 2011.05) bootargs Kernel command line: console=ttyS0,115200 noinitrd rw rootfstype=ext3 root=/dev/mmcblk0p2 rootwait mem=512M coherent_pool=4M no_console_suspend resume=/dev/mtdblock3. However, while booting I get the following error Failed to create /dev/root: -2VFS: Cannot open root device "mmcblk0p2" or unknown-block(179,2): error -2 I have also attached log for reference. Can anyone please point out what I may be missing? Regards,Amit.

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What is this MODULE_ALIAS() use for?
by Perr Zhang Dec. 10, 2016

Dec. 10, 2016

source code: MODULE_ALIAS("platform:sm501"); static const struct of_device_id of_sm501_match_tbl[] = { { .compatible = "smi,sm501", }, { /* end */ } }; MODULE_DEVICE_TABLE(of, of_sm501_match_tbl);

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marvell wifi sdio device not detected
by Dushara Jayasinghe Dec. 9, 2016

Dec. 9, 2016

Hi, I'm trying to bring up a marvell 8787 based wifi chip on an atmel sama5d2 based board. The kernel version I'm on is 4.4 (specific version is at https://github.com/linux4sam/linux-at91/tree/linux4sam_5.5) The wifi controller is a WYSBMVGXB from TAIYO YUDEN. The device tree configuration for the mmc bus I've used is as follows: sdmmc1: sdio-host@b0000000 { pinctrl-names = "default"; pinctrl-0 = <&pinctrl_sdmmc1_default>; mmc-pwrseq = <&sdhci0_pwrseq>; bus-width = <4>; broken-cd; status = "okay"; /* conflict with qspi0 */ }; I've used a modified pwrseq driver that drives the IO as specified in the controller data sheet and confirmed that the lines are controlled as expected during startup. I can also see some clock activity on the sdio bus, but doesn't seem to detect a device on the bus. The mwifiex_sdio driver is statically compiled. Can anyone offer any suggestions on how I can debug this issue? Also, I don't quite understand how the mwifiex_sdio driver is attached to that specific bus. My understanding based on the i2c, spi buses are, the device tree can specify the devices hanging off these buses and the appropriate driver is loaded. However, the mmc/sdio dts entries dob't seem to be following the same pattern. Thank you and regards, Dushara

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How to use spi device from another kernel module?
by Ran Shalit Dec. 8, 2016

Dec. 8, 2016

Hello, I have spi device which is registered using spi_register_board_info(), and I would like to get a pointer to this device in some other kernel module. Is there a simple way to get a pointer to pointer to a device , so that we can use it from other module ? (something like i2c_get_adapter for i2c) Regards, Ran

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bifs mount error
by Anurag Raghavan (RBEI/ETW11) Dec. 7, 2016

Dec. 7, 2016

Hi All, My appdata partition could not be mounted or where the partition was not able to be used. Anyone can help me to find out the root cause of this. What are the possibilities of this ubifs corruption. Any patched are available to fix this issue. Error logs: [ 1.797141] UBI error: ubi_io_read: error -74 (ECC error) while reading 253952 bytes from PEB 445:8192, read 253952 bytes [ 1.808274] UBIFS error (pid 491): ubifs_scan: corrupt empty space at LEB 489:233760 [ 1.816037] UBIFS error (pid 491): ubifs_scanned_corruption: corruption at LEB 489:233760 [ 1.828660] UBIFS error (pid 491): ubifs_scan: LEB 489 scanning failed [ 1.835215] UBIFS warning (pid 491): ubifs_ro_mode: switched to read-only mode, error -117 [ 1.843502] UBIFS error (pid 491): make_reservation: cannot reserve 58 bytes in jhead 2, error -117 [ 1.852569] UBIFS error (pid 491): do_writepage: cannot write page 0 of inode 76584, error -117 dpkg: error: unable to sync new file '/var/lib/dpkg/arch-new': Structure needs cleaning Best regards Raghavan Anurag RBEI/ETW1 Tel. +91(422)667-4001 | Mobil 9986968950

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Monitoring network system calls from outside VM
by W. Michael Petullo Dec. 6, 2016

Dec. 6, 2016

I am working on a system which will monitor the system calls serviced by an operating system running inside a VM. All of the software runs outside of the VM, and I wish to avoid modifying or installing software inside of the VM. Imagine an external monitor observing PID/syscall/syscall parameters and PID/syscall return values. We have a prototype running which uses Xen introspection. One difficulty is mapping packets back to the process which generated them. After observing a series of system calls, the monitor might want to deny a process's ability to send network traffic. A problem arises because the parameters to and return values from socket() and connect() or sendto() do not reveal the ephemeral port chosen by the operating system. Thus the monitor does not know which process created which packet. I had thought about watching packets. The first one which the VM generates destined to the parameters set by connect() or sendto() would likely be from the process which called connect() or sendto(). However, I am not sure the events would always work out in the right order. I think something like this might be possible even while assuming one core: Process A connect(1.1.1.1:80) Process B connect(1.1.1.1:80) Kernel sends B's three-way handshake Kernel sends A's three-way handshake Process B connect returns Process A connect returns If this happened, then the monitor would incorrectly associate B's source port with A and vice versa (because the connects and handshakes are out of order). Could the events work their way through the kernel in the way described above, assuming the OS is running on a single core? Or is the kernel written in such a way that it would preserve the expected ordering? With interrupts and scheduling points, I fear it is the former. Does anyone have an idea of how I could in the monitor associate source ports/packets with processes? The monitor can easily use VM introspection to do things like map PIDs to process names, but walking the kernel data structures to solve our packet problem using introspection is much harder. More importantly, such introspection is also fragile as data structures change across versions of Linux. Thank you, -- Mike :wq

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pls help in veth
by Er Krishna Dec. 6, 2016

Dec. 6, 2016

Hi All, Can some one pls let me know for below command to run on linux which driver and which package I need to install ? I see I have iproute package installed on my box, but still I am facing below error. root@krishna:~# ip link add ep1 type veth peer name ep2 RTNETLINK answers: Operation not supported BR/Krish

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Re: Driver with hard RT requiremnets
by Greg KH Dec. 5, 2016

Dec. 5, 2016

On Mon, Dec 05, 2016 at 04:49:28PM +0200, Ran Shalit wrote: > > > On Mon, Dec 5, 2016 at 4:35 PM, Greg KH <greg(a)kroah.com> wrote: > > On Mon, Dec 05, 2016 at 04:24:05PM +0200, Ran Shalit wrote: > > Hello, > > > > We need to support serial driver with real time requirements (towards > specific > > device with RT demands): > > Every 5.3msec receive 100 bytes and 1.3msec afterwards send 100 bytes. > > > > 1. Does kernel support real-time of such hard requirements ? > > It depends on the hardware you are using, does your hardware provide > enough processing power and lack of harware interruptions (i.e. SMI) to > allow this to work properly? > > > 2. Is it matter if we do the exact bytes send/receive from kernel or > userspace, > > i.e. is kernel more real-time than userspace ? > > It depends on your userspace code, people write real-time Java code in > userspace just fine. > > > 3. Is mainline kernel unable to support such requirements and we better > use RT > > patch such as xemonai ? > > Why not try it out yourself and see? You have the code and the hardware > to test, you don't need us to tell you if this works or not :) > > > Hi, > > I mean that the requirements doesn't allow missing of these time intervals for > send/receive. > Say If I'll test and it shall work OK, does it mean that in a more loaded usage > (more threads in a future application), it shall still function correctly with > the same kernel (from mainline) ? Again, it all depends on your hardware. But if you want to make sure your deadlines are met, use the -rt patchset and do a lot of testing to ensure things work properly. Don't just trust some random person on a random mailing list to tell you if it works or not :) > I also wanted to ask if it is doing real-time in kernel is better than doing it > in userspace ? Again, it all depends on what you are wanting to do, and your hardware. Battleships are doing real-time work, in Java, on Linux, just fine. Does that mean that any Linux machine can do that same workload with the same deadlines? Of course not, you have to consider the whole system (hardware and software) to be able to determine any of this. > Since we have some doubts if kernel can support such hard requirements, I > raised this question. I know that Xenomai was created to make kernel hard > real-time. I have no idea what xenomai is, again, please look into the -rt patchset, and your hardware platform requirements. good luck! greg k-h

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Driver with hard RT requiremnets
by Ran Shalit Dec. 5, 2016

Dec. 5, 2016

Hello, We need to support serial driver with real time requirements (towards specific device with RT demands): Every 5.3msec receive 100 bytes and 1.3msec afterwards send 100 bytes. 1. Does kernel support real-time of such hard requirements ? 2. Is it matter if we do the exact bytes send/receive from kernel or userspace, i.e. is kernel more real-time than userspace ? 3. Is mainline kernel unable to support such requirements and we better use RT patch such as xemonai ? Best Regards, Ran

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How to control power of a device from sysfs ?
by Ran Shalit Dec. 5, 2016

Dec. 5, 2016

Hello, I am trying to turn off screen using sysfs entries, but I'm having some difficulties with it: 1. command: echo 0 > /sys/devices/platform/s5p-dsim.0/ea8061/backlight/panel/brightness result: screen is dimmed - BUT not turned off 2. command: cat /sys/devices/platform/s5p-dsim.0/ea8061/backlight/panel/actual_brightness 20 This strengthen the fast that we didn't turned off brightness completely 3. In this point I though that maybe I can turn off the whole brightness device ls /sys/devices/platform/s5p-dsim.0/ea8061/backlight/panel/ actual_brightness auto_brightness bl_power brightness device dimming max_brightness power subsystem type uevent I made some trials , but didn't made it turned off yet. Is there any idea if it's possible to turn it off completely ? Thank you, Ran

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