1.. SPDX-License-Identifier: GPL-2.0 2 3.. _netdev-FAQ: 4 5============================= 6Networking subsystem (netdev) 7============================= 8 9tl;dr 10----- 11 12 - designate your patch to a tree - ``[PATCH net]`` or ``[PATCH net-next]`` 13 - for fixes the ``Fixes:`` tag is required, regardless of the tree 14 - don't post large series (> 15 patches), break them up 15 - don't repost your patches within one 24h period 16 - reverse xmas tree 17 18netdev 19------ 20 21netdev is a mailing list for all network-related Linux stuff. This 22includes anything found under net/ (i.e. core code like IPv6) and 23drivers/net (i.e. hardware specific drivers) in the Linux source tree. 24 25Note that some subsystems (e.g. wireless drivers) which have a high 26volume of traffic have their own specific mailing lists and trees. 27 28Like many other Linux mailing lists, the netdev list is hosted at 29kernel.org with archives available at https://lore.kernel.org/netdev/. 30 31Aside from subsystems like those mentioned above, all network-related 32Linux development (i.e. RFC, review, comments, etc.) takes place on 33netdev. 34 35Development cycle 36----------------- 37 38Here is a bit of background information on 39the cadence of Linux development. Each new release starts off with a 40two week "merge window" where the main maintainers feed their new stuff 41to Linus for merging into the mainline tree. After the two weeks, the 42merge window is closed, and it is called/tagged ``-rc1``. No new 43features get mainlined after this -- only fixes to the rc1 content are 44expected. After roughly a week of collecting fixes to the rc1 content, 45rc2 is released. This repeats on a roughly weekly basis until rc7 46(typically; sometimes rc6 if things are quiet, or rc8 if things are in a 47state of churn), and a week after the last vX.Y-rcN was done, the 48official vX.Y is released. 49 50To find out where we are now in the cycle - load the mainline (Linus) 51page here: 52 53 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 54 55and note the top of the "tags" section. If it is rc1, it is early in 56the dev cycle. If it was tagged rc7 a week ago, then a release is 57probably imminent. If the most recent tag is a final release tag 58(without an ``-rcN`` suffix) - we are most likely in a merge window 59and ``net-next`` is closed. 60 61git trees and patch flow 62------------------------ 63 64There are two networking trees (git repositories) in play. Both are 65driven by David Miller, the main network maintainer. There is the 66``net`` tree, and the ``net-next`` tree. As you can probably guess from 67the names, the ``net`` tree is for fixes to existing code already in the 68mainline tree from Linus, and ``net-next`` is where the new code goes 69for the future release. You can find the trees here: 70 71- https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git 72- https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git 73 74Relating that to kernel development: At the beginning of the 2-week 75merge window, the ``net-next`` tree will be closed - no new changes/features. 76The accumulated new content of the past ~10 weeks will be passed onto 77mainline/Linus via a pull request for vX.Y -- at the same time, the 78``net`` tree will start accumulating fixes for this pulled content 79relating to vX.Y 80 81An announcement indicating when ``net-next`` has been closed is usually 82sent to netdev, but knowing the above, you can predict that in advance. 83 84.. warning:: 85 Do not send new ``net-next`` content to netdev during the 86 period during which ``net-next`` tree is closed. 87 88RFC patches sent for review only are obviously welcome at any time 89(use ``--subject-prefix='RFC net-next'`` with ``git format-patch``). 90 91Shortly after the two weeks have passed (and vX.Y-rc1 is released), the 92tree for ``net-next`` reopens to collect content for the next (vX.Y+1) 93release. 94 95If you aren't subscribed to netdev and/or are simply unsure if 96``net-next`` has re-opened yet, simply check the ``net-next`` git 97repository link above for any new networking-related commits. You may 98also check the following website for the current status: 99 100 https://netdev.bots.linux.dev/net-next.html 101 102The ``net`` tree continues to collect fixes for the vX.Y content, and is 103fed back to Linus at regular (~weekly) intervals. Meaning that the 104focus for ``net`` is on stabilization and bug fixes. 105 106Finally, the vX.Y gets released, and the whole cycle starts over. 107 108netdev patch review 109------------------- 110 111.. _patch_status: 112 113Patch status 114~~~~~~~~~~~~ 115 116Status of a patch can be checked by looking at the main patchwork 117queue for netdev: 118 119 https://patchwork.kernel.org/project/netdevbpf/list/ 120 121The "State" field will tell you exactly where things are at with your 122patch: 123 124================== ============================================================= 125Patch state Description 126================== ============================================================= 127New, Under review pending review, patch is in the maintainer’s queue for 128 review; the two states are used interchangeably (depending on 129 the exact co-maintainer handling patchwork at the time) 130Accepted patch was applied to the appropriate networking tree, this is 131 usually set automatically by the pw-bot 132Needs ACK waiting for an ack from an area expert or testing 133Changes requested patch has not passed the review, new revision is expected 134 with appropriate code and commit message changes 135Rejected patch has been rejected and new revision is not expected 136Not applicable patch is expected to be applied outside of the networking 137 subsystem 138Awaiting upstream patch should be reviewed and handled by appropriate 139 sub-maintainer, who will send it on to the networking trees; 140 patches set to ``Awaiting upstream`` in netdev's patchwork 141 will usually remain in this state, whether the sub-maintainer 142 requested changes, accepted or rejected the patch 143Deferred patch needs to be reposted later, usually due to dependency 144 or because it was posted for a closed tree 145Superseded new version of the patch was posted, usually set by the 146 pw-bot 147RFC not to be applied, usually not in maintainer’s review queue, 148 pw-bot can automatically set patches to this state based 149 on subject tags 150================== ============================================================= 151 152Patches are indexed by the ``Message-ID`` header of the emails 153which carried them so if you have trouble finding your patch append 154the value of ``Message-ID`` to the URL above. 155 156Updating patch status 157~~~~~~~~~~~~~~~~~~~~~ 158 159Contributors and reviewers do not have the permissions to update patch 160state directly in patchwork. Patchwork doesn't expose much information 161about the history of the state of patches, therefore having multiple 162people update the state leads to confusion. 163 164Instead of delegating patchwork permissions netdev uses a simple mail 165bot which looks for special commands/lines within the emails sent to 166the mailing list. For example to mark a series as Changes Requested 167one needs to send the following line anywhere in the email thread:: 168 169 pw-bot: changes-requested 170 171As a result the bot will set the entire series to Changes Requested. 172This may be useful when author discovers a bug in their own series 173and wants to prevent it from getting applied. 174 175The use of the bot is entirely optional, if in doubt ignore its existence 176completely. Maintainers will classify and update the state of the patches 177themselves. No email should ever be sent to the list with the main purpose 178of communicating with the bot, the bot commands should be seen as metadata. 179 180The use of the bot is restricted to authors of the patches (the ``From:`` 181header on patch submission and command must match!), maintainers of 182the modified code according to the MAINTAINERS file (again, ``From:`` 183must match the MAINTAINERS entry) and a handful of senior reviewers. 184 185Bot records its activity here: 186 187 https://netdev.bots.linux.dev/pw-bot.html 188 189Review timelines 190~~~~~~~~~~~~~~~~ 191 192Generally speaking, the patches get triaged quickly (in less than 19348h). But be patient, if your patch is active in patchwork (i.e. it's 194listed on the project's patch list) the chances it was missed are close to zero. 195 196The high volume of development on netdev makes reviewers move on 197from discussions relatively quickly. New comments and replies 198are very unlikely to arrive after a week of silence. If a patch 199is no longer active in patchwork and the thread went idle for more 200than a week - clarify the next steps and/or post the next version. 201 202For RFC postings specifically, if nobody responded in a week - reviewers 203either missed the posting or have no strong opinions. If the code is ready, 204repost as a PATCH. 205 206Emails saying just "ping" or "bump" are considered rude. If you can't figure 207out the status of the patch from patchwork or where the discussion has 208landed - describe your best guess and ask if it's correct. For example:: 209 210 I don't understand what the next steps are. Person X seems to be unhappy 211 with A, should I do B and repost the patches? 212 213.. _Changes requested: 214 215Changes requested 216~~~~~~~~~~~~~~~~~ 217 218Patches :ref:`marked<patch_status>` as ``Changes Requested`` need 219to be revised. The new version should come with a change log, 220preferably including links to previous postings, for example:: 221 222 [PATCH net-next v3] net: make cows go moo 223 224 Even users who don't drink milk appreciate hearing the cows go "moo". 225 226 The amount of mooing will depend on packet rate so should match 227 the diurnal cycle quite well. 228 229 Signed-off-by: Joe Defarmer <joe@barn.org> 230 --- 231 v3: 232 - add a note about time-of-day mooing fluctuation to the commit message 233 v2: https://lore.kernel.org/netdev/123themessageid@barn.org/ 234 - fix missing argument in kernel doc for netif_is_bovine() 235 - fix memory leak in netdev_register_cow() 236 v1: https://lore.kernel.org/netdev/456getstheclicks@barn.org/ 237 238The commit message should be revised to answer any questions reviewers 239had to ask in previous discussions. Occasionally the update of 240the commit message will be the only change in the new version. 241 242Partial resends 243~~~~~~~~~~~~~~~ 244 245Please always resend the entire patch series and make sure you do number your 246patches such that it is clear this is the latest and greatest set of patches 247that can be applied. Do not try to resend just the patches which changed. 248 249Handling misapplied patches 250~~~~~~~~~~~~~~~~~~~~~~~~~~~ 251 252Occasionally a patch series gets applied before receiving critical feedback, 253or the wrong version of a series gets applied. 254 255Making the patch disappear once it is pushed out is not possible, the commit 256history in netdev trees is immutable. 257Please send incremental versions on top of what has been merged in order to fix 258the patches the way they would look like if your latest patch series was to be 259merged. 260 261In cases where full revert is needed the revert has to be submitted 262as a patch to the list with a commit message explaining the technical 263problems with the reverted commit. Reverts should be used as a last resort, 264when original change is completely wrong; incremental fixes are preferred. 265 266Stable tree 267~~~~~~~~~~~ 268 269While it used to be the case that netdev submissions were not supposed 270to carry explicit ``CC: stable@vger.kernel.org`` tags that is no longer 271the case today. Please follow the standard stable rules in 272:ref:`Documentation/process/stable-kernel-rules.rst <stable_kernel_rules>`, 273and make sure you include appropriate Fixes tags! 274 275Security fixes 276~~~~~~~~~~~~~~ 277 278Do not email netdev maintainers directly if you think you discovered 279a bug that might have possible security implications. 280The current netdev maintainer has consistently requested that 281people use the mailing lists and not reach out directly. If you aren't 282OK with that, then perhaps consider mailing security@kernel.org or 283reading about http://oss-security.openwall.org/wiki/mailing-lists/distros 284as possible alternative mechanisms. 285 286 287Co-posting changes to user space components 288~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 289 290User space code exercising kernel features should be posted 291alongside kernel patches. This gives reviewers a chance to see 292how any new interface is used and how well it works. 293 294When user space tools reside in the kernel repo itself all changes 295should generally come as one series. If series becomes too large 296or the user space project is not reviewed on netdev include a link 297to a public repo where user space patches can be seen. 298 299In case user space tooling lives in a separate repository but is 300reviewed on netdev (e.g. patches to ``iproute2`` tools) kernel and 301user space patches should form separate series (threads) when posted 302to the mailing list, e.g.:: 303 304 [PATCH net-next 0/3] net: some feature cover letter 305 └─ [PATCH net-next 1/3] net: some feature prep 306 └─ [PATCH net-next 2/3] net: some feature do it 307 └─ [PATCH net-next 3/3] selftest: net: some feature 308 309 [PATCH iproute2-next] ip: add support for some feature 310 311Posting as one thread is discouraged because it confuses patchwork 312(as of patchwork 2.2.2). 313 314Preparing changes 315----------------- 316 317Attention to detail is important. Re-read your own work as if you were the 318reviewer. You can start with using ``checkpatch.pl``, perhaps even with 319the ``--strict`` flag. But do not be mindlessly robotic in doing so. 320If your change is a bug fix, make sure your commit log indicates the 321end-user visible symptom, the underlying reason as to why it happens, 322and then if necessary, explain why the fix proposed is the best way to 323get things done. Don't mangle whitespace, and as is common, don't 324mis-indent function arguments that span multiple lines. If it is your 325first patch, mail it to yourself so you can test apply it to an 326unpatched tree to confirm infrastructure didn't mangle it. 327 328Finally, go back and read 329:ref:`Documentation/process/submitting-patches.rst <submittingpatches>` 330to be sure you are not repeating some common mistake documented there. 331 332Indicating target tree 333~~~~~~~~~~~~~~~~~~~~~~ 334 335To help maintainers and CI bots you should explicitly mark which tree 336your patch is targeting. Assuming that you use git, use the prefix 337flag:: 338 339 git format-patch --subject-prefix='PATCH net-next' start..finish 340 341Use ``net`` instead of ``net-next`` (always lower case) in the above for 342bug-fix ``net`` content. 343 344Dividing work into patches 345~~~~~~~~~~~~~~~~~~~~~~~~~~ 346 347Put yourself in the shoes of the reviewer. Each patch is read separately 348and therefore should constitute a comprehensible step towards your stated 349goal. 350 351Avoid sending series longer than 15 patches. Larger series takes longer 352to review as reviewers will defer looking at it until they find a large 353chunk of time. A small series can be reviewed in a short time, so Maintainers 354just do it. As a result, a sequence of smaller series gets merged quicker and 355with better review coverage. Re-posting large series also increases the mailing 356list traffic. 357 358Local variable ordering ("reverse xmas tree", "RCS") 359~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 360 361Netdev has a convention for ordering local variables in functions. 362Order the variable declaration lines longest to shortest, e.g.:: 363 364 struct scatterlist *sg; 365 struct sk_buff *skb; 366 int err, i; 367 368If there are dependencies between the variables preventing the ordering 369move the initialization out of line. 370 371Format precedence 372~~~~~~~~~~~~~~~~~ 373 374When working in existing code which uses nonstandard formatting make 375your code follow the most recent guidelines, so that eventually all code 376in the domain of netdev is in the preferred format. 377 378Using device-managed and cleanup.h constructs 379~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 380 381Netdev remains skeptical about promises of all "auto-cleanup" APIs, 382including even ``devm_`` helpers, historically. They are not the preferred 383style of implementation, merely an acceptable one. 384 385Use of ``guard()`` is discouraged within any function longer than 20 lines, 386``scoped_guard()`` is considered more readable. Using normal lock/unlock is 387still (weakly) preferred. 388 389Low level cleanup constructs (such as ``__free()``) can be used when building 390APIs and helpers, especially scoped iterators. However, direct use of 391``__free()`` within networking core and drivers is discouraged. 392Similar guidance applies to declaring variables mid-function. 393 394Resending after review 395~~~~~~~~~~~~~~~~~~~~~~ 396 397Allow at least 24 hours to pass between postings. This will ensure reviewers 398from all geographical locations have a chance to chime in. Do not wait 399too long (weeks) between postings either as it will make it harder for reviewers 400to recall all the context. 401 402Make sure you address all the feedback in your new posting. Do not post a new 403version of the code if the discussion about the previous version is still 404ongoing, unless directly instructed by a reviewer. 405 406The new version of patches should be posted as a separate thread, 407not as a reply to the previous posting. Change log should include a link 408to the previous posting (see :ref:`Changes requested`). 409 410Testing 411------- 412 413Expected level of testing 414~~~~~~~~~~~~~~~~~~~~~~~~~ 415 416At the very minimum your changes must survive an ``allyesconfig`` and an 417``allmodconfig`` build with ``W=1`` set without new warnings or failures. 418 419Ideally you will have done run-time testing specific to your change, 420and the patch series contains a set of kernel selftest for 421``tools/testing/selftests/net`` or using the KUnit framework. 422 423You are expected to test your changes on top of the relevant networking 424tree (``net`` or ``net-next``) and not e.g. a stable tree or ``linux-next``. 425 426patchwork checks 427~~~~~~~~~~~~~~~~ 428 429Checks in patchwork are mostly simple wrappers around existing kernel 430scripts, the sources are available at: 431 432https://github.com/linux-netdev/nipa/tree/master/tests 433 434**Do not** post your patches just to run them through the checks. 435You must ensure that your patches are ready by testing them locally 436before posting to the mailing list. The patchwork build bot instance 437gets overloaded very easily and netdev@vger really doesn't need more 438traffic if we can help it. 439 440netdevsim 441~~~~~~~~~ 442 443``netdevsim`` is a test driver which can be used to exercise driver 444configuration APIs without requiring capable hardware. 445Mock-ups and tests based on ``netdevsim`` are strongly encouraged when 446adding new APIs, but ``netdevsim`` in itself is **not** considered 447a use case/user. You must also implement the new APIs in a real driver. 448 449We give no guarantees that ``netdevsim`` won't change in the future 450in a way which would break what would normally be considered uAPI. 451 452``netdevsim`` is reserved for use by upstream tests only, so any 453new ``netdevsim`` features must be accompanied by selftests under 454``tools/testing/selftests/``. 455 456Reviewer guidance 457----------------- 458 459Reviewing other people's patches on the list is highly encouraged, 460regardless of the level of expertise. For general guidance and 461helpful tips please see :ref:`development_advancedtopics_reviews`. 462 463It's safe to assume that netdev maintainers know the community and the level 464of expertise of the reviewers. The reviewers should not be concerned about 465their comments impeding or derailing the patch flow. 466 467Less experienced reviewers are highly encouraged to do more in-depth 468review of submissions and not focus exclusively on trivial or subjective 469matters like code formatting, tags etc. 470 471Testimonials / feedback 472----------------------- 473 474Some companies use peer feedback in employee performance reviews. 475Please feel free to request feedback from netdev maintainers, 476especially if you spend significant amount of time reviewing code 477and go out of your way to improve shared infrastructure. 478 479The feedback must be requested by you, the contributor, and will always 480be shared with you (even if you request for it to be submitted to your 481manager). 482