October 2019 - kernelnewbies@kernelnewbies.org

[PATCH] feedback appreciated
by Alex Diaz Oct. 18, 2019

Oct. 18, 2019

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Why linux kernel mailing list stop send email to me
by wuzhouhui Oct. 17, 2019

Oct. 17, 2019

Hi, Few days ago, I subscribe linux kernel mailing list (linux-kernel(a)vger.kernel.org) Subscription succeed and I got a lot of email from linux kernel. However, I don't get any new email since yesterday and it is impossible for linux kernel mailing list. So the reason should be that I have unsubscribed passively. I only receive email and never send email to linux kernel. So why I can't receive new emails? Thanks.

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Re: Try/catch for modules?
by Maria Neptune Oct. 17, 2019

Oct. 17, 2019

On Thu, Oct 17, 2019, 09:42 Maria Neptune <maria.elysse.n(a)gmail.com> wrote: > I hate to say it but honestly in a kernel module, your solution is not to > do null dereferences. It's hard but you gotta. > Otherwise I've seen quite a bit of error handling done with gotos (if > ptr==0 goto error), which I believe compiles to similar code as try/except > blocks. Unsure how you'd handle stuff that sends a signal like null > dereferences in that way though. > > On Thu, Oct 17, 2019, 09:37 Martin Galvan <omgalvan.86(a)gmail.com> wrote: > >> Hi all, >> >> I'm writing a kernel module, and am trying to implement some >> exception-handling mechanism so that the system won't oops/panic if my >> module does e.g. a NULL dereference. The (horribly hackish) way I'm >> doing this right now is registering a die_notifier which will set the >> 'panic_on_oops' variable to 0 if we detect that the current PID >> corresponds to my module. However, this is ugly for many reasons. >> >> What would be the "standard" way of doing this? Is there something >> like Window's try/except blocks, where I can get back control of the >> execution flow, without having the process die? I'm aware of >> _ASM_EXTABLE, but I understand this only works for a single >> instruction and has other limitations. >> >> _______________________________________________ >> Kernelnewbies mailing list >> Kernelnewbies(a)kernelnewbies.org >> https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >> >

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Do I need strong mathematical bases to work in the memory subsystem?
by CRISTIAN ANDRES VARGAS GONZALEZ Oct. 16, 2019

Oct. 16, 2019

Hello good morning, to be developed from the kernel do I need to have good math bases? I want to help in the ram memory subsystem and I have that doubt thank you.

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Re: Kernelnewbies Digest, Vol 107, Issue 9
by CRISTIAN ANDRES VARGAS GONZALEZ Oct. 10, 2019

Oct. 10, 2019

Thank you very much, I understand better, I will continue checking the links that happened to me regards att cristian vargas El mié., 9 oct. 2019 a las 11:00, <kernelnewbies-request(a)kernelnewbies.org> escribió: > Send Kernelnewbies mailing list submissions to > kernelnewbies(a)kernelnewbies.org > > To subscribe or unsubscribe via the World Wide Web, visit > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > or, via email, send a message with subject or body 'help' to > kernelnewbies-request(a)kernelnewbies.org > > You can reach the person managing the list at > kernelnewbies-owner(a)kernelnewbies.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Kernelnewbies digest..." > > > Today's Topics: > > 1. Re: Are there global constructors in the Linux kernel? > (Konstantin Andreev) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Wed, 09 Oct 2019 11:54:26 +0300 > From: Konstantin Andreev <andreev(a)swemel.ru> > To: CRISTIAN ANDRES VARGAS GONZALEZ <vargascristian(a)americana.edu.co>, > kernelnewbies(a)kernelnewbies.org > Subject: Re: Are there global constructors in the Linux kernel? > Message-ID: <5D9DA042.2090205(a)swemel.ru> > Content-Type: text/plain; charset=utf-8; format=flowed > > Hi, Cristian. There are, a kinda of ... > > kernel/taskstats.c: > | late_initcall(taskstats_init); > > kernel/rcu/update.c: > | early_initcall(check_cpu_stall_init); > > There is a whole set of macros STAGE_initcall() in include/linux/init.h > > Arguments to these macros invokations are accounted and called by kernel > initialization code at strictly defined stages of initialization. See > https://0xax.gitbooks.io/linux-insides/content/Concepts/linux-cpu-3.html > > The only thing that is run before kernel is <a series of> > platform-specific boot loaders, maybe under hypervisor control. Compiler > has no power to insert something in between. > > Regards, Konstantin. > > CRISTIAN ANDRES VARGAS GONZALEZ, 09 Oct 2019 06:44 MSK: > > > > Good day > > > > I have been doing a little kernel following some repositories of > GitHub, videos and wikis, and I have found a topic that leaves me with > doubts, the theme is the global constructors. > > > > Suppose I write a program in c, for the user space, for my code to run I > must have the main function > > int main() { /*Code*/} > > > > The gcc compiler searches for this function to run my program, but > before that happens, I can use the global constructors and write a code > that runs before the main function, but in the case of writing a kernel, > why do I need to run lines of code before the kernel is executed ?, I > understand that when writing a kernel there is no main function and that it > is disabled to indicate it to the compiler. In the Linux kernel are there > global constructors? If so, what things are executed before starting the > kernel? > > att: cristian vargas. > > > > ------------------------------ > > Subject: Digest Footer > > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies(a)kernelnewbies.org > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > > ------------------------------ > > End of Kernelnewbies Digest, Vol 107, Issue 9 > ********************************************* >

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Software Prefetching using Machine learning
by Irfan Ullah (울라 이르판) Oct. 10, 2019

Oct. 10, 2019

Dear All, Thanks in advance. I am a PhD candidate, and currently I have started working on kernel development. My professor told me to implement this paper <https://arxiv.org/abs/1803.02329>. In this paper authors have used machine learning to predict the next missed addresses.They used instruction addresses (program counters PCs), and corresponding missed addresses as features to train the machine learning classifier. As a kernel newbie, I don't know how to initiate the implementation. I am thinking to implement it in the following steps: 1- Saving instruction addresses (PCs), and corresponding missed addresses 2- Perform the machine learning 3-Do the prediction using machine learning classifier, and swap in/swap out the pages. I have some questions that 1) How can I directly store the missed addresses, and instruction addresses from kernel handle_mm_fault() to a file? 2) How can I use machine learning classifier in the kernel for predicting addresses? 3) Is there any way to do the machine learning in the user space in python, and then transfer the classifier in bytes forms to the kernel space for address predictions ? Currently, I am stuck in getting the missed addresses by storing it into the file. I am trying to send the missed addresses to the user space from the kernel space, and store it into the file. I know that /proc, ioctl, and netlink are some options to exchange data between kernel and user spaces. I have selected the netlink, and trying to customize this code <https://gist.github.com/JeonghunLee/17db624665da91ee46c221b00e2b93f5> for my task. I need some type of communication API which let me do exchange anytype of data (integers, string, bytes, and may be structures to bind all these types of data) between kernel space, and user space. Any type of help, and guidelines will be highly appreciated. Thank you. -- *Best Regards,* *Mr. Irfan Ullah* PhD Candidate Data and Knowledge Engineering(DKE) Lab Department of Computer Science and Engineering Kyung Hee University, South Korea. +82-010-591-51651 <+82%2010-3877-8867> sahibzada.iu(a)gmail.com sahibzada_irfanullah

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Predicting Process crash / Memory utlization using machine learning
by prathamesh naik Oct. 10, 2019

Oct. 10, 2019

Hi all, I want to work on project which can predict kernel process crash or even user space process crash (or memory usage spikes) using machine learning algorithms. Can someone point me what all data can be useful for tuning my algorithm ? is there already paper on this (could not find much articles on this) ? Thanks, Prathamesh

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Are there global constructors in the Linux kernel?
by CRISTIAN ANDRES VARGAS GONZALEZ Oct. 9, 2019

Oct. 9, 2019

Good day I have been doing a little kernel following some repositories of GitHub, videos and wikis, and I have found a topic that leaves me with doubts, the theme is the global constructors. Suppose I write a program in c, for the user space, for my code to run I must have the main function int main() { /*Code*/} The gcc compiler searches for this function to run my program, but before that happens, I can use the global constructors and write a code that runs before the main function, but in the case of writing a kernel, why do I need to run lines of code before the kernel is executed ?, I understand that when writing a kernel there is no main function and that it is disabled to indicate it to the compiler. In the Linux kernel are there global constructors? If so, what things are executed before starting the kernel? att: cristian vargas.

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Re: Kernelnewbies Digest, Vol 107, Issue 5
by CRISTIAN ANDRES VARGAS GONZALEZ Oct. 7, 2019

Oct. 7, 2019

Thank you very much for the answers, it has been very useful. El sáb., 5 oct. 2019 a las 11:00, <kernelnewbies-request(a)kernelnewbies.org> escribió: > Send Kernelnewbies mailing list submissions to > kernelnewbies(a)kernelnewbies.org > > To subscribe or unsubscribe via the World Wide Web, visit > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > or, via email, send a message with subject or body 'help' to > kernelnewbies-request(a)kernelnewbies.org > > You can reach the person managing the list at > kernelnewbies-owner(a)kernelnewbies.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Kernelnewbies digest..." > > > Today's Topics: > > 1. Re: Remote I/O bus (Valdis Kl=?utf-8?Q?=c4=93?=tnieks) > 2. Test the kernel code (CRISTIAN ANDRES VARGAS GONZALEZ) > 3. Re: Test the kernel code (Adam Zerella) > 4. Re: Test the kernel code (Valdis Kl=?utf-8?Q?=c4=93?=tnieks) > 5. suspend mode (nunojsa) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Fri, 04 Oct 2019 17:51:17 -0400 > From: "Valdis Kl=?utf-8?Q?=c4=93?=tnieks" <valdis.kletnieks(a)vt.edu> > To: Luca Ceresoli <luca(a)lucaceresoli.net> > Cc: Greg KH <greg(a)kroah.com>, kernelnewbies(a)kernelnewbies.org > Subject: Re: Remote I/O bus > Message-ID: <154634.1570225877@turing-police> > Content-Type: text/plain; charset="us-ascii" > > On Fri, 04 Oct 2019 17:08:30 +0200, Luca Ceresoli said: > > Yes, the read/write helpers are nicely isolated. However this sits in a > > vendor kernel that tends to change a lot from one release to another, so > > I admit having a hard time wrapping my head around "vendor kernel that > changes a lot from one release to another", unless you mean something like > the RedHat Enterprise releases that updates every 2 years, and at that > point you get hit > with a jump of 8 or 10 kernel releases. > > And of course, the right answer is to fix up the driver and upstream it, > so that > in 2022 when your vendor does a new release, the updated driver will > already be > there waiting for you. > > And don't worry about having to do patches to update the driver to a new > kernel > release because APIs change - that's only a problem for out-of-tree > drivers. If it's > in-tree, the person making the API change is supposed to fix your driver > for you. > >

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Remote I/O bus
by Luca Ceresoli Oct. 7, 2019

Oct. 7, 2019

Hi, on an embedded system I currently have a standard platform device: .-----. data .--------. | CPU |--------| DEVICE | '-----' bus '--------' The driver is a standard platform driver that uses ioread32() and iowrite32() to access registers. So far, so good. Now in a new design I have the same device in an FPGA, external to the SoC. The external FPGA is not reachable via an I/O bus, but via SPI (or I2C). A microprocessor in the FPGA acts as a bridge: as an SPI client it receives register read/write requests from the CPU, forwards them to the devices on the in-FPGA data bus as a master, then sends back the replies over SPI. SoC <- | -> FPGA .-----. data .---------. .--------. data .--------. | CPU |---------| SPI CTL |-------| BRIDGE |---------| DEVICE | '-----' bus A '---------' SPI '--------' bus B '--------' What would be a proper way to model this in the Linux kernel? Of course I can hack the drivers to hijack them on SPI, but I'm trying to solve the problem in a better way. IMO "a proper way" implies that the platform driver does not need to be aware of the existence of the bridge. Note: in the real case there is more than one device to handle. At first sight I think this should be modeled with a "bridge" device that: * is a SPI device * implements a "platform bus" where regular platform devices can be instantiated, similar to a "simple-bus" In device tree terms: &amba { /* data bus A in picture */ spi0: spi@42000000 { reg = <0x42000000 0x1000>; #address-cells = <1>; io-over-spi-bridge@1 { /* data bus B */ reg = <1>; /* slave select pin 1 */ compatible = "linux,io-over-spi-bridge"; #address-cells = <1>; #size-cells = <1>; mydevice@4000 { /* 1 kB I/O space at 0x4000 on bus B */ reg = <0x4000 0x1000>; }; }; }; }; The io-over-spi driver is supposed to request allocation of a virtual memory area that: 1. is as large as the address space on bus B 2. is __iomem (non cached, etc) 3. is not mapped on the physical CPU address space (bus A) 4. page faults at every read/write access, triggering a callback that starts an SPI transaction, waits for the result and returns After some research I haven't found how this could be implemented, mostly due to my newbieness about kernel memory management. Also, as drivers might access the bus in IRQ handlers, I suspect there is no way to do an SPI transaction in IRQ context, but this could be handled differently (threaded IRQ...). Does this look like a good approach to handle the problem? If it does, how would you implement the iomem access and handle IRQ context? Otherwise, which way would you suggest? Many thanks in advance, -- Luca

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