January 2023 - kernelnewbies@kernelnewbies.org

Source code organization
by Billie Alsup (balsup) April 23, 2024

April 23, 2024

I have a set of drivers that I would like to upstream. These are primarily MFD style drivers supporting Cisco-8000 FPGAs. The devices can be instantiated through multiple top level drivers, which provide the access mechanism for the MFD driver. For example, an FPGA can be accessed via PCI, or via i2c, or via SLPC, or via P2PM (a point-to-point interface). We currently build these drivers out of tree, under a single directory drivers/cisco. I note that existing drivers are spread out across the kernel tree, sometimes by bus (pci, i2c), sometimes by function (gpio, net/mdio, spi), and sometimes under the generic mfd. I would like to start the upstream review process for our drivers, but first want to get recommendations on the source code layout. Is it permissible to keep a top level directory such as drivers/cisco to organize our code? It is not only the source code that is affected, but also provides a central place for Kconfig entries. Our FPGAs have multiple logical blocks, each of which is handled by a different MFD driver, e.g. i2c controllers, gpio controllers, spi controllers, mdio controllers. There can be multiple instances of each block as well (so multiple MFD devices are instantiated for each driver). And of course, there can be multiple FPGAs in a system, each with different combinations of logical blocks. The drivers themselves are pretty specific to our FPGAs, thus it makes sense to use Kconfig to select a hardware platform to automatically select the set of MFD drivers (and top level bus drivers) that would apply. Would a source layout putting all the code under drivers/cisco be acceptable in this case, or do I need to move things around and spread out the Kconfig entries across directories? I note that a single drivers/cisco would simplify any related modifications to MAINTAINERS as well.

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a question in pcie-designware-ep.c, can't find where a variable has been set.
by Chan Kim Jan. 31, 2023

Jan. 31, 2023

Hello kernel users and experts, With linux-5.15.68, I was analyzing function dw_plat_pcie_probe in file drivers/pci/controller/dwc/pcie-designware-plat.c. This function creates struct dw_pcie and it has struct dw_pcie_ep embedded in it as member 'ep'. When it's endpoint, it calls dw_pcie_ep_init(&pci->ep). ( https://elixir.bootlin.com/linux/v5.15.68/source/drivers/pci/controller/dwc/ pcie-designware-plat.c#L166 ) return dw_pcie_ep_init(&pci->ep); Now in the dw_pcie_ep_init function, (drivers/pci/controller/dwc/pcie-designware-ep.c) It creates dw_pcie_epc and calls pci_epc_mem_init function like this. ( https://elixir.bootlin.com/linux/v5.15.68/source/drivers/pci/controller/dwc/ pcie-designware-ep.c#L770 ) ret = pci_epc_mem_init(epc, ep->phys_base, ep->addr_size, ep->page_size); But I can't find where ep->page_size was assigned earlier. (ep is the pointer to the struct dw_pcie_ep). Can anyone tell me where it was assigned? And I'm not clear in this struct pci_epc_mem_window, the unit of size.(in include/linux/pci-epc.h) struct pci_epc_mem_window { phys_addr_t phys_base; size_t size; size_t page_size; }; Is the size in byte unit? Or is it number of pages? Thank you. Chan Kim

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uninterruptible process
by Axel M. Jan. 30, 2023

Jan. 30, 2023

Hi all, I'm looking for system call that can make my process uninterrupted until it completes successfully. My app receives a SIGTERM signal (when an shutdown is triggerd), then needs to write into a file with a simple fopen(). Actually it can't write in my file because I think it is automatically killed (SIGKILL) by systemd. Do you have any advice on this ? Thanks -- Thanks, Axel M.

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Guideline on Linux NAT feature
by Abdul Matin Jan. 27, 2023

Jan. 27, 2023

Hi, I'm a novice in Kernel development. This is the first time I'm writing here. I need to develop something similar to FTP ALG on Active mode. That is, I will inspect some packets while passing through the NAT then based on some conditions I will set permission for an IP of another device/NAT on the internet so that it can send packets directly to an internal device. I'm reading some books on Linux kernel device driver development. I know I'll have to do that using the Netfilter subsystem of the linux kernel. To learn how ftp alg is implemented I've been searching for source in kernel source, although I found code that mangles the packet of PORT command of FTP connection but I can't find where the mapping thing is done for Active mode of FTP. Which file should I read to know about how FTP alg for active mode makes a server connect to a client behind NAT? I'd appreciate any replies.

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Re: custom compil
by aurel.pere＠gmail.com Jan. 26, 2023

Jan. 26, 2023

Ok thanks for these infos i will check it out When saying automatic i was referring to kernel updates in package repositories (with apt or dnf) where auto download and install can be configured for security updates...i was thinking about applying config options but i guess they are already compiled? Isnt there a tool that would download new kernel based on repository security updates and that would compile it with a provided config file? I can use a bash script or ansible role but i dont see how to keep close to the official kernel distribution updates automatically... Thanks 25 janv. 2023 23:21:15 Siddh Raman Pant <code(a)siddh.me>: > On Thu, 26 Jan 2023 at 03:25:08 +0530, A.Péré wrote: >> Is there a distribution with automated tools to compile a kernel >> with custom config settings > > Yes, it is your favourite distro, whichever that may be. You just > need the tools to build, which you may already have, but can be seen > in docs: https://www.kernel.org/doc/html/latest/process/changes.html > >> that ils easier and more accessible > > If you want a GUI, use `make xconfig`. > >> un particular for automated updates with automatic custom compiling config? > > Have your custom config options in a separate file somewhere, and use > scripts/kconfig/merge_config.sh to merge. Example in a script: > > make defconfig > ./scripts/kconfig/merge_config.sh .config common.config > > The script will take care of requisite stuff, which additional options > to enable, etc. > > Or you can have your entire config saved in .config, and just run > merge_config.sh everytime you pull newer kernel code. > > Thanks, > Siddh

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Isolating abstract sockets
by Stefan Bavendiek Jan. 26, 2023

Jan. 26, 2023

Hi, Im trying to find a solution to a problem in the context of user space sandbox engineering on Linux and would appreciate any comments to guide me into the right direction in order to possible create a kernel patch that solves this problem: When building userspace application sandboxes, one issue that does not seem trivial to solve is the isolation of abstract sockets. While most IPC mechanism can be isolated by mechanisms like mount namespaces, abstract sockets are part of the network namespace. It is possible to isolate abstract sockets by using a new network namespace, however, unprivileged processes can only create a new empty network namespace, which removes network access as well and makes this useless for network clients. Same linux sandbox projects try to solve this by bridging the existing network interfaces into the new namespace or use something like slirp4netns to archive this, but this does not look like an ideal solution to this problem, especially since sandboxing should reduce the kernel attack surface without introducing more complexity. Aside from containers using namespaces, sandbox implementations based on seccomp and landlock would also run into the same problem, since landlock only provides file system isolation and seccomp cannot filter the path argument and therefore it can only be used to block new unix domain socket connections completely. Currently there does not seem to be any way to disable network namespaces in the kernel without also disabling unix domain sockets. The question is how to solve the issue of abstract socket isolation in a clean and efficient way, possibly even without namespaces. What would be the ideal way to implement a mechanism to disable abstract sockets either globally or even better, in the context of a process. Thank you - Stefan

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custom compil
by A.Péré Jan. 25, 2023

Jan. 25, 2023

Hi, I would like to compile a kernel for fedora following this security guide ( https://www.ssi.gouv.fr/guide/recommandations-de-securite-relatives-a-un-sy… v2) I have some parameters that i have put using an ansible role (https://github.com/robertdebock/ansible-role-kernel) The compilation works but when i reboot i get a black screen so i guess i am not doing it the right way. Ideally I would like to be able to compile new kernel on the fly with my custom .config file for almalinux server and my fedora workstation home pc. I have seen this fedora doc (https://docs.fedoraproject.org/en-US/quick-docs/kernel/build-custom-kernel/) but at the paragraph "Building a Kernel from the Fedora dist-git" it states 3. Make whatever changes or customizations you need, but no information is provided on how to do that. Could you help me in doing this? Thank you

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Services / processes shutdown
by Axel M. Jan. 25, 2023

Jan. 25, 2023

Hi all, I'm trying to understand how the services and the processes are stopped when a shutdown(init 0) is initiated. Do you have any advice on this ? Thanks, -- Thanks, Axel M.

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Query on New LTS version
by Arun Sudhilal Jan. 23, 2023

Jan. 23, 2023

Hi, What is the latest LTS version? https://www.kernel.org/category/releases.html The above page still says it is 5.15. https://lwn.net/Articles/915435/ But the above lwn page says 6.1 is 2022 LTS. kernel.org link is no more updated? Regards, Arun

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Re: POSIX.1b book/documentation
by Axel M. Jan. 20, 2023

Jan. 20, 2023

On 1/20/2023 1:05 PM, Alexander Kapshuk wrote: > Is this,https://pubs.opengroup.org/onlinepubs/9699919799/, what > you're looking for? I'm looking for a book like 1* [1] https://archive.org/details/posix1standardpr0000zlot/mode/2up But I don't know if it contains the explanations of POSIX.1b ? Thanks for your help. -- Thanks, Axel M.

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