July 2020 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

How to make /dev/ttyACM0 (and friends) exclusive?
by Jeffrey Walton Oct. 11, 2020

Oct. 11, 2020

Hi Everyone, I'm trying to trackdown a problem using my dialup modem. I have a program that opens the modem and watches caller id's. It flashes the hook when a telemarketer calls. It works well until... When another program opens the modem then my program starts reading intermittent responses intended for the other program. I cannot seem to open the device in exclusive mode. The current open is (I also tried with O_EXCL): int modem = open(device_path, O_RDWR | O_NOCTTY | O_SYNC); I'm not sure if it because udev configures the device incorrectly or the kernel driver is configured incorrectly. Or maybe it is impossible to do. Does anyone know how I can make the device exclusive? Thanks in advance.

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Compiled Kernel stuck in booting
by Yashodhan Joshi Sept. 23, 2020

Sept. 23, 2020

Hello, I use a dual boot laptop with windows and Ubuntu,with grub2. I Followed the instruction in https://kernelnewbies.org/OutreachyfirstpatchSetup to clone the source code and compile the kernel, which was done without any errors. When I tried to install the kernel using 'sudo make modules_install install' it showed a warning when updating initramfs, that it will attempt to resume from UUID, which is my SWAP space, but other than that it showed no other errors. When I tried to boot into it from the grub menu after restarting, it showed message of loading the kernel and then 'setting up intitial ramdisk', after which nothing further happend. The default kernel that came with ubuntu is still working and boots up into desktop environment withing 2-3 minutes after the 'ramdisk' message, but even though I kept the system running for 20 minutes after the 'ramdisk' message for the compiled kernel, niether any further proccess seems to be happening nor any error messages are shown. Can someone help me figuring out what is wrong and how can I run the kernel? Thank You. Also can someone point me in right direction to send suggestions about updating the information on kernelnewbies website? The information about connecting mutt to Gmail is quite outdated, and I would like to help updating it.

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How to check my wifi driver iwlwifi supports "wifi 5G band 4"
by Malatesh Ankasapur July 29, 2020

July 29, 2020

Hi Guys, How can check my wifi chip and driver is supports "wifi 5G band 4" Indonsia. What is the differnce between band 1/2/4 ? Regards, Malatesh

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test tools to measure performance of the Linux kernel
by Subhashini Rao Beerisetty July 27, 2020

July 27, 2020

Hi all, I’m having a few Linux x86_64 systems(same hardware configuration) with different Ubuntu kernels installed on those machines. I’m looking for any existing test suite which can be used to measure the system performance on different kernels. Any pointers on this topic will be greatly appreciated. Thanks

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[PATCH 0/3] dyndbg: WIP semi-viable diet plan ?
by Jim Cromie July 25, 2020

July 25, 2020

dynamic-debug metadata is bloated; the __dyndbg linker section, filled by DYNAMIC_DEBUG_METADATA, has 3 fields with 90%, 84%, 45% repeated values, consuming ~150kb on my laptop. Instead of an arduous restructuring of the data, lets stuff it into zram, get whatever compression it gives us for free, and be able to map and unmap individual records on demand. Once map/unmap suffices for internal needs, the whole __dyndbg section can be reclaimed. >From this, it seems practical to push it into zswap, and then to keep active/enabled callsites mapped into ram, like a cache. But thats a lot of stuff I can only handwave about. Please fill in details or call BS. This patchset makes a decent start down that path, but theres a boatload of chatter in the commit-logs about options and maybes, and brave projections about whats possible. Blah Blah. Theres almost certainly some subtle/ornot thinkos. Please point them out. I probably have some terminology cleanup to do too. I punted with lazy names a lot & welcome better ones some // comments too - not for submission I'll try to summarize here. - The easiest thing is to stuff whole struct _ddebug contents, into an anonymous struct, along with a new zhandle, into a new zpool. This is done in patch 1. this defers the unionization, so it just enlarges the ram footprint. - patch 2 attempts to distinguish zhandles from pointers, by making zhandles odd, and testing with %2. This works fine before unionization, falls over afterwards. - The unionization is in patch 3, and it works, at least casually. The fix-on-2 is to add an explicit flag; is_zhandle, and drop the %2 test, which fails when it encounters an odd pointer in the __dyndbg section. the structs/unions must be reworked to actually save any ram - for non-JUMP_LABEL builds, putting whole struct _ddebug into zram is problematic; it means pulling out whole record just to check the am-i-printing flag, a horrible cost. - pulling flags into a separate flags vector would solve that, and would be 'tight' on ram; no paholes, good grouping of flags for callsites enabled with module=foo function=bar file=buz etc. But it creates new ones Im stuck on. - an 'opaque' descriptor might be the magic needed, but Im pretty clueless on how to proceed. Anyone got any pointers to good examples in the tree ? This patchset is on top of other dyndbg patches, which are now in gregkh's char-misc git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git in the char-misc-next branch. Jim Cromie (3): dyndbg: WIP replace __dyndbg section with a zs-pool copy. dyndbg: zhandle+1 plus info tweaks, BUG_ONs dyndbg: fixup/correct assumptions re ptr-vals include/linux/dynamic_debug.h | 9 ++ lib/dynamic_debug.c | 172 ++++++++++++++++++++++++++++++++-- 2 files changed, 171 insertions(+), 10 deletions(-) -- 2.26.2

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Unable to manually bind driver
by Isaac July 22, 2020

July 22, 2020

Hello everyone, I'm currently going through the task 05 of the eudalypta challenge. I thought my implementation didn't work, so I tried testing a a person's solution on github <https://github.com/agelastic/eudyptula/tree/master/task5>. However, I am still unable to manually bind the USB device to my driver. Here are the steps I did. 1) Use* lsusb -t *to find the bus and port USB device was connected on. It was *1-3*. 2) Went to *sys/bus/usb/devices* and found that *1-3 *was bound to *drivers/usb* using *tree*. 3) Used *echo 1-3 > unbind* to unbind it. 4) Went to *devices* folder and checked if it was still bound. It was not. 5) Went to the directory of my own driver, named *hello_driver*. 6) Tried to do *echo 1-3 > bind* but got the error message *echo: write error: No such device*. These instructions are based on LWN.net Manual driver binding and unbinding <https://lwn.net/Articles/143397/>. One suspicion I have is that this simple USB driver doesn't support the USB device I am plugging in (a USB flash drive). I actually have no idea. Many thanks for your help.

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i2c possible patch
by Nuno Sá July 22, 2020

July 22, 2020

Hi all, I was looking at the i2c core code and I stumbled in a condition that looks like some "legacy" thing. While I'm not sure about this, this mailing list feels like a good place to get some feedback. The condition in question is this https://elixir.bootlin.com/linux/latest/source/drivers/i2c/i2c-core-base.c#… So, my first question is: Can we actually get into `i2c_device_probe()` without `i2c_device_match()` being called first? If not, it looks that this condition could just be removed... If we can get there without `i2c_device_match()`, I can see a problem in the condition if we just use of_id_table in ACPI. `i2c_acpi_match_device()` just calls `acpi_match_device()` whereas I think `acpi_driver_match_device()` should be used if we want to take of_id_table into account. Does this really look like an issue or Am I missing something? - Nuno Sá

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Dubios pointer casting with put_user()
by Richard Sailer July 19, 2020

July 19, 2020

Hi, In the following example from net/dccp/proto.c the pointer given put_user() is casted to (int __user *) although the value to copy is a unsigned long. Is this (correctness and security wise) sane? Because as I understand it put_user() determines the amount it copies from the pointer type. ``` unsigned long amount = 0; skb = skb_peek(&sk->sk_receive_queue); if (skb != NULL) { amount = skb->len; } rc = put_user(amount, (int __user *)arg); ``` Also skb->len is an unsigned int realisticly in most cases < 9000 (and in all cases I can imagine < int_max (with 16 bit)). I would like to declare amount as int outside of the switch case statement (because I need it in another case statement as signed int) would it be safe to do so? Thanks, -- Richard

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Why disabling CONFIG_APIC may cause the kernel failing to boot up?
by 孙世龙 sunshilong July 19, 2020

July 19, 2020

Hi, list The same kernel Deb is installed on two different platforms(both are intel X86_64 CPUs, but not the same model). But what confuses is that it works well on one platform whereas it causes the kernel failing to boot up on the other one. Could you please shed some light on this matter? Thank you for your attention to this matter. sunshilong

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How to comfirm whether __GI___clock_gettime() implemented as fast system call or not on x86_64 platform with Linux 4.19.84?
by 孙世龙 sunshilong July 19, 2020

July 19, 2020

Hi, list How to comfirm whether __GI___clock_gettime() implemented as fast system call or not on x86_64 platform with Linux 4.19.84? Here is some related backtrace log(hope there is some hint on this question): (gdb) bt #0 0x00007ffc41da89fa in ?? () #1 0x00007fa90785aaf0 in ?? () #2 0x00007fa905a16876 in __GI___clock_gettime (clock_id=0, tp=0x7fa90785aac0) at ../sysdeps/unix/clock_gettime.c:115 Thank you for your attention to this matter.

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