2. Networking subsystem (netdev)¶
- designate your patch to a tree -
- 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 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.
The netdev list is managed (like many other Linux mailing lists) through VGER (http://vger.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.
2.3. 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
-rcN suffix) - we are most likely in a merge window
net-next is closed.
2.4. 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.
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
--subject-prefix='RFC net-next' with
Shortly after the two weeks have passed (and vX.Y-rc1 is released), the
net-next reopens to collect content for the next (vX.Y+1)
If you aren’t subscribed to netdev and/or are simply unsure if
net-next has re-opened yet, simply check the
repository link above for any new networking-related commits. You may
also check the following website for the current status:
net tree continues to collect fixes for the vX.Y content, and is
fed back to Linus at regular (~weekly) intervals. Meaning that the
net is on stabilization and bug fixes.
Finally, the vX.Y gets released, and the whole cycle starts over.
2.5. netdev patch review¶
2.5.1. 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. 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.
2.5.2. Updating patch status¶
It may be tempting to help the maintainers and update the state of your own 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. Leave it to the maintainer to figure out what is the most recent and current version that should be applied. If there is any doubt, the maintainer will reply and ask what should be done.
2.5.3. 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. Asking the maintainer for status updates on your patch is a good way to ensure your patch is ignored or pushed to the bottom of the priority list.
2.5.4. 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.
2.5.5. 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 fix the patches the way they would look like if your latest patch series was to be merged.
2.5.6. Stable tree¶
While it used to be the case that netdev submissions were not supposed
to carry explicit
CC: email@example.com tags that is no longer
the case today. Please follow the standard stable rules in
and make sure you include appropriate Fixes tags!
2.5.7. 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 firstname.lastname@example.org or reading about http://oss-security.openwall.org/wiki/mailing-lists/distros as possible alternative mechanisms.
2.5.8. 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).
2.6. 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
--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.
2.6.1. 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
net instead of
net-next (always lower case) in the above for
2.6.2. 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.
2.6.3. Multi-line comments¶
Comment style convention is slightly different for networking and most of the 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 */
2.6.4. 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.
2.6.5. 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.
2.6.6. 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.
2.7.1. 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
net-next) and not e.g. a stable tree or
2.7.2. patchwork checks¶
Checks in patchwork are mostly simple wrappers around existing kernel scripts, the sources are available at:
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.
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
netdevsim features must be accompanied by selftests under
2.8. 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).