1. Networking subsystem (netdev)

1.1. 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

1.2. netdev

netdev is a mailing list for all network-related Linux stuff. This includes anything found under net/ (i.e. core code like IPv6) and drivers/net (i.e. hardware specific drivers) in the Linux source tree.

Note that some subsystems (e.g. wireless drivers) which have a high volume of traffic have their own specific mailing lists and trees.

Like many other Linux mailing lists, the netdev list is hosted at kernel.org with archives available at https://lore.kernel.org/netdev/.

Aside from subsystems like those mentioned above, all network-related Linux development (i.e. RFC, review, comments, etc.) takes place on netdev.

1.3. Development cycle

Here is a bit of background information on the cadence of Linux development. Each new release starts off with a two week “merge window” where the main maintainers feed their new stuff to Linus for merging into the mainline tree. After the two weeks, the merge window is closed, and it is called/tagged -rc1. No new features get mainlined after this -- only fixes to the rc1 content are expected. 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 a state of churn), and a week after the last vX.Y-rcN was done, the official vX.Y is released.

To find out where we are now in the cycle - load the mainline (Linus) page here:

and note the top of the “tags” section. If it is rc1, it is early in the dev cycle. If it was tagged rc7 a week ago, then a release is probably imminent. If the most recent tag is a final release tag (without an -rcN suffix) - we are most likely in a merge window and net-next is closed.

1.4. git trees and patch flow

There are two networking trees (git repositories) in play. Both are driven by David Miller, the main network maintainer. There is the net tree, and the net-next tree. As you can probably guess from the names, the net tree is for fixes to existing code already in the mainline tree from Linus, and net-next is where the new code goes for the future release. You can find the trees here:

Relating that to kernel development: At the beginning of the 2-week merge window, the net-next tree will be closed - no new changes/features. The accumulated new content of the past ~10 weeks will be passed onto mainline/Linus via a pull request for vX.Y -- at the same time, the net tree will start accumulating fixes for this pulled content relating to vX.Y

An announcement indicating when net-next has been closed is usually sent 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), the tree 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 git repository link above for any new networking-related commits. You may also check the following website for the current status:

The net tree continues to collect fixes for the vX.Y content, and is fed back to Linus at regular (~weekly) intervals. Meaning that the focus for net is on stabilization and bug fixes.

Finally, the vX.Y gets released, and the whole cycle starts over.

1.5. netdev patch review

1.5.1. Patch status

Status of a patch can be checked by looking at the main patchwork queue for netdev:

The “State” field will tell you exactly where things are at with your patch:

Patch state

Description

New, Under review

pending review, patch is in the maintainer’s queue for review; the two states are used interchangeably (depending on the exact co-maintainer handling patchwork at the time)

Accepted

patch was applied to the appropriate networking tree, this is usually set automatically by the pw-bot

Needs ACK

waiting for an ack from an area expert or testing

Changes requested

patch has not passed the review, new revision is expected with appropriate code and commit message changes

Rejected

patch has been rejected and new revision is not expected

Not applicable

patch is expected to be applied outside of the networking subsystem

Awaiting upstream

patch should be reviewed and handled by appropriate sub-maintainer, who will send it on to the networking trees; patches set to Awaiting upstream in netdev’s patchwork will usually remain in this state, whether the sub-maintainer requested changes, accepted or rejected the patch

Deferred

patch needs to be reposted later, usually due to dependency or because it was posted for a closed tree

Superseded

new version of the patch was posted, usually set by the pw-bot

RFC

not to be applied, usually not in maintainer’s review queue, pw-bot can automatically set patches to this state based on subject tags

Patches are indexed by the Message-ID header of the emails which carried them so if you have trouble finding your patch append the value of Message-ID to the URL above.

1.5.2. Updating patch status

Contributors and reviewers do not have the permissions to update patch state directly in patchwork. Patchwork doesn’t expose much information about the history of the state of patches, therefore having multiple people update the state leads to confusion.

Instead of delegating patchwork permissions netdev uses a simple mail bot which looks for special commands/lines within the emails sent to the mailing list. For example to mark a series as Changes Requested one needs to send the following line anywhere in the email thread:

pw-bot: changes-requested

As a result the bot will set the entire series to Changes Requested. This may be useful when author discovers a bug in their own series and wants to prevent it from getting applied.

The use of the bot is entirely optional, if in doubt ignore its existence completely. Maintainers will classify and update the state of the patches themselves. No email should ever be sent to the list with the main purpose of communicating with the bot, the bot commands should be seen as metadata.

The use of the bot is restricted to authors of the patches (the From: header on patch submission and command must match!), maintainers of the modified code according to the MAINTAINERS file (again, From: must match the MAINTAINERS entry) and a handful of senior reviewers.

Bot records its activity here:

1.5.3. Review timelines

Generally speaking, the patches get triaged quickly (in less than 48h). But be patient, if your patch is active in patchwork (i.e. it’s listed on the project’s patch list) the chances it was missed are close to zero.

The high volume of development on netdev makes reviewers move on from discussions relatively quickly. New comments and replies are very unlikely to arrive after a week of silence. If a patch is no longer active in patchwork and the thread went idle for more than a week - clarify the next steps and/or post the next version.

For RFC postings specifically, if nobody responded in a week - reviewers either missed the posting or have no strong opinions. If the code is ready, repost as a PATCH.

Emails saying just “ping” or “bump” are considered rude. If you can’t figure out the status of the patch from patchwork or where the discussion has landed - describe your best guess and ask if it’s correct. For example:

I don't understand what the next steps are. Person X seems to be unhappy
with A, should I do B and repost the patches?

1.5.4. Changes requested

Patches marked as Changes Requested need to be revised. The new version should come with a change log, preferably including links to previous postings, for example:

[PATCH net-next v3] net: make cows go moo

Even users who don't drink milk appreciate hearing the cows go "moo".

The amount of mooing will depend on packet rate so should match
the diurnal cycle quite well.

Signed-off-by: Joe Defarmer <joe@barn.org>
---
v3:
  - add a note about time-of-day mooing fluctuation to the commit message
v2: https://lore.kernel.org/netdev/123themessageid@barn.org/
  - fix missing argument in kernel doc for netif_is_bovine()
  - fix memory leak in netdev_register_cow()
v1: https://lore.kernel.org/netdev/456getstheclicks@barn.org/

The commit message should be revised to answer any questions reviewers had to ask in previous discussions. Occasionally the update of the commit message will be the only change in the new version.

1.5.5. Partial resends

Please always resend the entire patch series and make sure you do number your patches such that it is clear this is the latest and greatest set of patches that can be applied. Do not try to resend just the patches which changed.

1.5.6. Handling misapplied patches

Occasionally a patch series gets applied before receiving critical feedback, or the wrong version of a series gets applied.

Making the patch disappear once it is pushed out is not possible, the commit history in netdev trees is immutable. Please send incremental versions on top of what has been merged in order to fix the patches the way they would look like if your latest patch series was to be merged.

In cases where full revert is needed the revert has to be submitted as a patch to the list with a commit message explaining the technical problems with the reverted commit. Reverts should be used as a last resort, when original change is completely wrong; incremental fixes are preferred.

1.5.7. Stable tree

While it used to be the case that netdev submissions were not supposed to carry explicit CC: stable@vger.kernel.org tags that is no longer the case today. Please follow the standard stable rules in Documentation/process/stable-kernel-rules.rst, and make sure you include appropriate Fixes tags!

1.5.8. Security fixes

Do not email netdev maintainers directly if you think you discovered a bug that might have possible security implications. The current netdev maintainer has consistently requested that people use the mailing lists and not reach out directly. If you aren’t OK with that, then perhaps consider mailing security@kernel.org or reading about http://oss-security.openwall.org/wiki/mailing-lists/distros as possible alternative mechanisms.

1.5.9. Co-posting changes to user space components

User space code exercising kernel features should be posted alongside kernel patches. This gives reviewers a chance to see how any new interface is used and how well it works.

When user space tools reside in the kernel repo itself all changes should generally come as one series. If series becomes too large or the user space project is not reviewed on netdev include a link to a public repo where user space patches can be seen.

In case user space tooling lives in a separate repository but is reviewed on netdev (e.g. patches to iproute2 tools) kernel and user space patches should form separate series (threads) when posted to 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).

1.6. Preparing changes

Attention to detail is important. Re-read your own work as if you were the reviewer. You can start with using checkpatch.pl, perhaps even with the --strict flag. But do not be mindlessly robotic in doing so. If your change is a bug fix, make sure your commit log indicates the end-user visible symptom, the underlying reason as to why it happens, and then if necessary, explain why the fix proposed is the best way to get things done. Don’t mangle whitespace, and as is common, don’t mis-indent function arguments that span multiple lines. If it is your first patch, mail it to yourself so you can test apply it to an unpatched tree to confirm infrastructure didn’t mangle it.

Finally, go back and read Documentation/process/submitting-patches.rst to be sure you are not repeating some common mistake documented there.

1.6.1. Indicating target tree

To help maintainers and CI bots you should explicitly mark which tree your patch is targeting. Assuming that you use git, use the prefix flag:

git format-patch --subject-prefix='PATCH net-next' start..finish

Use net instead of net-next (always lower case) in the above for bug-fix net content.

1.6.2. Dividing work into patches

Put yourself in the shoes of the reviewer. Each patch is read separately and therefore should constitute a comprehensible step towards your stated goal.

Avoid sending series longer than 15 patches. Larger series takes longer to review as reviewers will defer looking at it until they find a large chunk of time. A small series can be reviewed in a short time, so Maintainers just do it. As a result, a sequence of smaller series gets merged quicker and with better review coverage. Re-posting large series also increases the mailing list traffic.

1.6.3. 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 ordering move the initialization out of line.

1.6.4. Format precedence

When working in existing code which uses nonstandard formatting make your code follow the most recent guidelines, so that eventually all code in the domain of netdev is in the preferred format.

1.6.5. Using device-managed and cleanup.h constructs

Netdev remains skeptical about promises of all “auto-cleanup” APIs, including even devm_ helpers, historically. They are not the preferred style of implementation, merely an acceptable one.

Use of guard() is discouraged within any function longer than 20 lines, scoped_guard() is considered more readable. Using normal lock/unlock is still (weakly) preferred.

Low level cleanup constructs (such as __free()) can be used when building APIs and helpers, especially scoped iterators. However, direct use of __free() within networking core and drivers is discouraged. Similar guidance applies to declaring variables mid-function.

1.6.6. Clean-up patches

Netdev discourages patches which perform simple clean-ups, which are not in the context of other work. For example:

  • Addressing checkpatch.pl warnings

  • Addressing Local variable ordering issues

  • Conversions to device-managed APIs (devm_ helpers)

This is because it is felt that the churn that such changes produce comes at a greater cost than the value of such clean-ups.

Conversely, spelling and grammar fixes are not discouraged.

1.6.7. Resending after review

Allow at least 24 hours to pass between postings. This will ensure reviewers from all geographical locations have a chance to chime in. Do not wait too long (weeks) between postings either as it will make it harder for reviewers to recall all the context.

Make sure you address all the feedback in your new posting. Do not post a new version of the code if the discussion about the previous version is still ongoing, unless directly instructed by a reviewer.

The new version of patches should be posted as a separate thread, not as a reply to the previous posting. Change log should include a link to the previous posting (see Changes requested).

1.7. Testing

1.7.1. 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 networking tree (net or net-next) and not e.g. a stable tree or linux-next.

1.7.2. patchwork checks

Checks in patchwork are mostly simple wrappers around existing kernel scripts, the sources are available at:

https://github.com/linux-netdev/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 locally before posting to the mailing list. The patchwork build bot instance gets overloaded very easily and netdev@vger really doesn’t need more traffic if we can help it.

1.7.3. netdevsim

netdevsim is a test driver which can be used to exercise driver configuration APIs without requiring capable hardware. Mock-ups and tests based on netdevsim are strongly encouraged when adding new APIs, but netdevsim in itself is not considered a 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 future in a way which would break what would normally be considered uAPI.

netdevsim is reserved for use by upstream tests only, so any new netdevsim features must be accompanied by selftests under tools/testing/selftests/.

1.8. Reviewer guidance

Reviewing other people’s patches on the list is highly encouraged, regardless of the level of expertise. For general guidance and helpful tips please see Reviewing patches.

It’s safe to assume that netdev maintainers know the community and the level of expertise of the reviewers. The reviewers should not be concerned about their comments impeding or derailing the patch flow.

Less experienced reviewers are highly encouraged to do more in-depth review of submissions and not focus exclusively on trivial or subjective matters like code formatting, tags etc.

1.9. 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 code and go out of your way to improve shared infrastructure.

The feedback must be requested by you, the contributor, and will always be shared with you (even if you request for it to be submitted to your manager).