.. SPDX-License-Identifier: GPL-2.0 .. _netdev-FAQ: =============================Networking subsystem (netdev)============================= tl;dr-----  - designate your patch to a tree - ``[PATCH net]`` or ``[PATCH net-next]`` - for fixes the ``Fixes:`` tag is required, regardless of the tree - don't post large series (> 15 patches), break them up - don't repost your patches within one 24h period - reverse xmas tree netdev------ netdev is a mailing list for all network-related Linux stuff.  Thisincludes anything found under net/ (i.e. core code like IPv6) anddrivers/net (i.e. hardware specific drivers) in the Linux source tree. Note that some subsystems (e.g. wireless drivers) which have a highvolume of traffic have their own specific mailing lists and trees. The netdev list is managed (like many other Linux mailing lists) throughVGER (http://vger.kernel.org/) with archives available athttps://lore.kernel.org/netdev/ Aside from subsystems like those mentioned above, all network-relatedLinux development (i.e. RFC, review, comments, etc.) takes place onnetdev. Development cycle----------------- Here is a bit of background information onthe cadence of Linux development.  Each new release starts off with atwo week "merge window" where the main maintainers feed their new stuffto Linus for merging into the mainline tree.  After the two weeks, themerge window is closed, and it is called/tagged ``-rc1``.  No newfeatures get mainlined after this -- only fixes to the rc1 content areexpected.  After roughly a week of collecting fixes to the rc1 content,rc2 is released.  This repeats on a roughly weekly basis until rc7(typically; sometimes rc6 if things are quiet, or rc8 if things are in astate of churn), and a week after the last vX.Y-rcN was done, theofficial vX.Y is released. To find out where we are now in the cycle - load the mainline (Linus)page here:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git and note the top of the "tags" section.  If it is rc1, it is early inthe dev cycle.  If it was tagged rc7 a week ago, then a release isprobably imminent. If the most recent tag is a final release tag(without an ``-rcN`` suffix) - we are most likely in a merge windowand ``net-next`` is closed. git trees and patch flow------------------------ There are two networking trees (git repositories) in play.  Both aredriven by David Miller, the main network maintainer.  There is the``net`` tree, and the ``net-next`` tree.  As you can probably guess fromthe names, the ``net`` tree is for fixes to existing code already in themainline tree from Linus, and ``net-next`` is where the new code goesfor the future release.  You can find the trees here: - https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git- https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git Relating that to kernel development: At the beginning of the 2-weekmerge window, the ``net-next`` tree will be closed - no new changes/features.The accumulated new content of the past ~10 weeks will be passed ontomainline/Linus via a pull request for vX.Y -- at the same time, the``net`` tree will start accumulating fixes for this pulled contentrelating to vX.Y An announcement indicating when ``net-next`` has been closed is usuallysent to netdev, but knowing the above, you can predict that in advance. .. warning::  Do not send new ``net-next`` content to netdev during the  period during which ``net-next`` tree is closed. RFC patches sent for review only are obviously welcome at any time(use ``--subject-prefix='RFC net-next'`` with ``git format-patch``). Shortly after the two weeks have passed (and vX.Y-rc1 is released), thetree for ``net-next`` reopens to collect content for the next (vX.Y+1)release. If you aren't subscribed to netdev and/or are simply unsure if``net-next`` has re-opened yet, simply check the ``net-next`` gitrepository link above for any new networking-related commits.  You mayalso check the following website for the current status:   http://vger.kernel.org/~davem/net-next.html The ``net`` tree continues to collect fixes for the vX.Y content, and isfed back to Linus at regular (~weekly) intervals.  Meaning that thefocus for ``net`` is on stabilization and bug fixes. Finally, the vX.Y gets released, and the whole cycle starts over. netdev patch review------------------- Patch status~~~~~~~~~~~~ Status of a patch can be checked by looking at the main patchworkqueue for netdev:   https://patchwork.kernel.org/project/netdevbpf/list/ The "State" field will tell you exactly where things are at with yourpatch. Patches are indexed by the ``Message-ID`` header of the emailswhich carried them so if you have trouble finding your patch appendthe value of ``Message-ID`` to the URL above. Updating patch status~~~~~~~~~~~~~~~~~~~~~ It may be tempting to help the maintainers and update the state of yourown patches when you post a new version or spot a bug. Please **do not**do that.Interfering with the patch status on patchwork will only cause confusion. Leaveit to the maintainer to figure out what is the most recent and currentversion that should be applied. If there is any doubt, the maintainerwill reply and ask what should be done. Review timelines~~~~~~~~~~~~~~~~ Generally speaking, the patches get triaged quickly (in less than48h). But be patient, if your patch is active in patchwork (i.e. it'slisted on the project's patch list) the chances it was missed are close to zero.Asking the maintainer for status updates on yourpatch is a good way to ensure your patch is ignored or pushed to thebottom of the priority list. Partial resends~~~~~~~~~~~~~~~ Please always resend the entire patch series and make sure you do number yourpatches such that it is clear this is the latest and greatest set of patchesthat can be applied. Do not try to resend just the patches which changed. Handling misapplied patches~~~~~~~~~~~~~~~~~~~~~~~~~~~ Occasionally a patch series gets applied before receiving critical feedback,or the wrong version of a series gets applied.There is no revert possible, once it is pushed out, it stays like that.Please send incremental versions on top of what has been merged in order to fixthe patches the way they would look like if your latest patch series was to bemerged. Stable tree~~~~~~~~~~~ While it used to be the case that netdev submissions were not supposedto carry explicit ``CC: stable@vger.kernel.org`` tags that is no longerthe case today. Please follow the standard stable rules in:ref:`Documentation/process/stable-kernel-rules.rst <stable_kernel_rules>`,and make sure you include appropriate Fixes tags! Security fixes~~~~~~~~~~~~~~ Do not email netdev maintainers directly if you think you discovereda bug that might have possible security implications.The current netdev maintainer has consistently requested thatpeople use the mailing lists and not reach out directly.  If you aren'tOK with that, then perhaps consider mailing security@kernel.org orreading about http://oss-security.openwall.org/wiki/mailing-lists/distrosas possible alternative mechanisms.  Co-posting changes to user space components~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ User space code exercising kernel features should be postedalongside kernel patches. This gives reviewers a chance to seehow any new interface is used and how well it works. When user space tools reside in the kernel repo itself all changesshould generally come as one series. If series becomes too largeor the user space project is not reviewed on netdev include a linkto a public repo where user space patches can be seen. In case user space tooling lives in a separate repository but isreviewed on netdev  (e.g. patches to ``iproute2`` tools) kernel anduser space patches should form separate series (threads) when postedto the mailing list, e.g.::   [PATCH net-next 0/3] net: some feature cover letter   └─ [PATCH net-next 1/3] net: some feature prep   └─ [PATCH net-next 2/3] net: some feature do it   └─ [PATCH net-next 3/3] selftest: net: some feature   [PATCH iproute2-next] ip: add support for some feature Posting as one thread is discouraged because it confuses patchwork(as of patchwork 2.2.2). Preparing changes----------------- Attention to detail is important.  Re-read your own work as if you were thereviewer.  You can start with using ``checkpatch.pl``, perhaps even withthe ``--strict`` flag.  But do not be mindlessly robotic in doing so.If your change is a bug fix, make sure your commit log indicates theend-user visible symptom, the underlying reason as to why it happens,and then if necessary, explain why the fix proposed is the best way toget things done.  Don't mangle whitespace, and as is common, don'tmis-indent function arguments that span multiple lines.  If it is yourfirst patch, mail it to yourself so you can test apply it to anunpatched tree to confirm infrastructure didn't mangle it. Finally, go back and read:ref:`Documentation/process/submitting-patches.rst <submittingpatches>`to be sure you are not repeating some common mistake documented there. Indicating target tree~~~~~~~~~~~~~~~~~~~~~~ To help maintainers and CI bots you should explicitly mark which treeyour patch is targeting. Assuming that you use git, use the prefixflag::   git format-patch --subject-prefix='PATCH net-next' start..finish Use ``net`` instead of ``net-next`` (always lower case) in the above forbug-fix ``net`` content. Dividing work into patches~~~~~~~~~~~~~~~~~~~~~~~~~~ Put yourself in the shoes of the reviewer. Each patch is read separatelyand therefore should constitute a comprehensible step towards your statedgoal. Avoid sending series longer than 15 patches. Larger series takes longerto review as reviewers will defer looking at it until they find a largechunk of time. A small series can be reviewed in a short time, so Maintainersjust do it. As a result, a sequence of smaller series gets merged quicker andwith better review coverage. Re-posting large series also increases the mailinglist traffic. Multi-line comments~~~~~~~~~~~~~~~~~~~ Comment style convention is slightly different for networking and most ofthe tree.  Instead of this::   /*   * foobar blah blah blah   * another line of text   */ it is requested that you make it look like this::   /* foobar blah blah blah   * another line of text   */ Local variable ordering ("reverse xmas tree", "RCS")~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Netdev has a convention for ordering local variables in functions.Order the variable declaration lines longest to shortest, e.g.::   struct scatterlist *sg;  struct sk_buff *skb;  int err, i; If there are dependencies between the variables preventing the orderingmove the initialization out of line. Format precedence~~~~~~~~~~~~~~~~~ When working in existing code which uses nonstandard formatting makeyour code follow the most recent guidelines, so that eventually all codein the domain of netdev is in the preferred format. Resending after review~~~~~~~~~~~~~~~~~~~~~~ Allow at least 24 hours to pass between postings. This will ensure reviewersfrom all geographical locations have a chance to chime in. Do not waittoo long (weeks) between postings either as it will make it harder for reviewersto recall all the context. Make sure you address all the feedback in your new posting. Do not post a newversion of the code if the discussion about the previous version is stillongoing, unless directly instructed by a reviewer. Testing------- Expected level of testing~~~~~~~~~~~~~~~~~~~~~~~~~ At the very minimum your changes must survive an ``allyesconfig`` and an``allmodconfig`` build with ``W=1`` set without new warnings or failures. Ideally you will have done run-time testing specific to your change,and the patch series contains a set of kernel selftest for``tools/testing/selftests/net`` or using the KUnit framework. You are expected to test your changes on top of the relevant networkingtree (``net`` or ``net-next``) and not e.g. a stable tree or ``linux-next``. patchwork checks~~~~~~~~~~~~~~~~ Checks in patchwork are mostly simple wrappers around existing kernelscripts, the sources are available at: https://github.com/kuba-moo/nipa/tree/master/tests **Do not** post your patches just to run them through the checks.You must ensure that your patches are ready by testing them locallybefore posting to the mailing list. The patchwork build bot instancegets overloaded very easily and netdev@vger really doesn't need moretraffic if we can help it. netdevsim~~~~~~~~~ ``netdevsim`` is a test driver which can be used to exercise driverconfiguration APIs without requiring capable hardware.Mock-ups and tests based on ``netdevsim`` are strongly encouraged whenadding new APIs, but ``netdevsim`` in itself is **not** considereda use case/user. You must also implement the new APIs in a real driver. We give no guarantees that ``netdevsim`` won't change in the futurein a way which would break what would normally be considered uAPI. ``netdevsim`` is reserved for use by upstream tests only, so anynew ``netdevsim`` features must be accompanied by selftests under``tools/testing/selftests/``. Testimonials / feedback----------------------- Some companies use peer feedback in employee performance reviews.Please feel free to request feedback from netdev maintainers,especially if you spend significant amount of time reviewing codeand go out of your way to improve shared infrastructure. The feedback must be requested by you, the contributor, and will alwaysbe shared with you (even if you request for it to be submitted to yourmanager).