February 2016 - kernelnewbies@kernelnewbies.org

How to handle Hotplug with UIO userspace driver
by Mandeep Sandhu Sept. 28, 2017

Sept. 28, 2017

Hi All, We're working on a custom PCIe based hardware, which can be hotplugged into the system. We're using the UIO approach of having a minimal kernel driver which basically handles the interrupt and provides a mmap of the device memory to userspace and userspace driver which mmap's the provided memory and manages the device. We're using systemd and udev rules to spawn off a user process whenever the hardware is plugged into the system. Now my question is, how can we gracefully inform the userspace process if someone pulls out the hardware (sitting on a PCI slot). Even with full hotplug support, there can always be a case of "surprise removal", where someone yanks the board without going through the whole "attention button" routine. While the kernel driver has no problem with hot-removal, I see that if I "unregister" our UIO driver in response to the removal, then the mapping for the hardware's physical memory would become "invalid" (done by UIO on unregsiter). This could possibly cause the user-space process to crash due to illegal memory access. Is there a "standard" way to handle this scenario, i.e for hotpluggable hardware using UIO? Basically, we'd want to "unregister" the UIO device only after the userspace process is informed of the removal so that it could unmap/close the device and exit gracefully. We could try doing it using some systemd trick, where we put a dependency on one of the UIO created files (/dev/uioX), so that when the file is destroyed, systemd could kill/shutdown the process. Although, there's no guarantee that the userspace process won't try to access the mmaped space during that interval, so this isn't a reliable solution either. Any hints, thoughts? Thanks., -mandeep

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What are need to makes humidifier?
by 윤영석 April 1, 2017

April 1, 2017

Hi, I want to make own humidifier. What sensor need when making humidifier?? humidity indicator (detecting humidity), ultrasonic waves maker?? Please shares your wisdom to me. Thanks. Best regards.

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[PATCH] staging: dgnc: Remove useless and deadly judgment
by Navy Cheng March 11, 2016

March 11, 2016

pci_unregister_driver() should be used once dgnc module exit. It has nothing to do with dgnc_NumBoards. Remove the judgment of dgnc_NumBoards to avoid pci_unregister_driver() is not used when dgnc_NumBoards is 0. Signed-off-by: Navy Cheng <navych(a)126.com> --- drivers/staging/dgnc/dgnc_driver.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/drivers/staging/dgnc/dgnc_driver.c b/drivers/staging/dgnc/dgnc_driver.c index fc6d298..20b0c3b 100644 --- a/drivers/staging/dgnc/dgnc_driver.c +++ b/drivers/staging/dgnc/dgnc_driver.c @@ -156,8 +156,7 @@ static void dgnc_cleanup_module(void) dgnc_tty_post_uninit(); - if (dgnc_NumBoards) - pci_unregister_driver(&dgnc_driver); + pci_unregister_driver(&dgnc_driver); } /* -- 2.1.4

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How to use earlycon and earlyprintk on Samsung S3C24xx
by Woody Wu March 7, 2016

March 7, 2016

Hi, It seems, at least in 4.4.2 kernel, earlyprintk parameter supports something like 's3c24xx,<addr>'. But I dont know where to find out the addr value of the first uart port on my *s3c2416* based board. Can someone please tell me? Also, I desire to know if the earlycon parameter supports the Samsung S3C24xx uarts, if so, what should the value of the parameter look like? Thank in advance, -woody -- Life is the only flaw in an otherwise perfect nonexistence -- Schopenhauer woody public key at http://subkeys.pgp.net:11371 (narkewoody(a)gmail.com)

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Question : How to access to bandwith statistics from kernel space?
by Martin Houry March 2, 2016

March 2, 2016

I have made some research and I could't find a library who can give me interfaces's statistics like max/min/average bandwidth, jitter, ... Do you know a way to do this? Thank you Martin

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Project Idea..
by SUNITA March 1, 2016

March 1, 2016

Respected Sir/Madam, I am trying to study the effect of Scheduler Policies on Energy Consumption of Portable Device. This will be achieved by modifying the current Completely Fair Scheduler by changing the range of nice values from 40 to 100 and adding a new scheduing policy. CFS uses SCHED_RR, SCHED_FCFS, SCHED_OTHER, SCHED_BATCH Policy for scheduling any process. The idea is to insert a new scheduling policy by modifying the header files. Can this be a good topic to carry out research.I welcome any other idea related Linux Kernel CFS. Regards, SUNIITA

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How to understan /proc/sys/kernel/sched_domain/cpu$/domain$/flags?
by Nan Xiao Feb. 26, 2016

Feb. 26, 2016

Hi all, I find there is a flags file under /proc/sys/kernel/sched_domain/cpu$/domain$ directory, but can't figure out the meaning of this file: # cat flags 687 Could anyone tell me where I can find the definition of this file? Thanks in advance! Best Regards Nan Xiao

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Mutex and Spinlock locked together
by priyaranjan Feb. 25, 2016

Feb. 25, 2016

Hello All, Do you have any idea of a situation where we would need mutex and spinlock to be locked together? I think there is an example for this in Linux kernel. Can anyone help me? Regards, Priyaranjan

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Is there a bug in dgnc.ko?
by Navy Cheng Feb. 25, 2016

Feb. 25, 2016

Hi, My kernel version is v4.4, and I have built drivers/staging/dgnc/dgnc.ko. I change to *dir*/drivers/staging/dgnc and do like this: sudo insmod ./dgnc.ko sudo lsmod | grep dgnc sudo rmmod ./dgnc sudo insmod ./dgnc.ko After I re-insmod the dgnc module, my laptop is breakdown. My OS is debian 8.0. Is there a bug in dgnc.ko or something wrong with my OS or kernel. If there is a bug, How can I find it? Thanks.

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user rsyslog/syslog
by Ran Shalit Feb. 24, 2016

Feb. 24, 2016

Hello, I am trying to write to rsyslog from application. With openlog(..., LOG_USER), it works fine and I find the log in /var/log/user.log (it is defines in /etc/rsyslog.d/50-defaults.conf ) But we need to enable different applications to have each its own log file. I tried to use LOG_LOCAL0 instead and configured it in /etc/rsyslog.d/50-defaults.conf the same way as user: local0.* action { type="omfile" FILE="/var/log/local0.log" FileOwner="root" FileGroup="adm" } I then did 1. /etc/init.d/rsyslog stop 2. /etc/init.d/rsyslog start I see no warnings or errors, and I started the application trying to write to LOG_LOCAL0, But there is no new file created, no logs. Is there any idea whatws wrong, or how I can achieve this multi user's logs ? Thank you, Ran

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