mainlining shenanigans
f40d9b2086
Currently this simplified code snippet fails: br_vlan_get_pvid(netdev, &pvid); br_vlan_get_info(netdev, pvid, &vinfo); ASSERT(!(vinfo.flags & BRIDGE_VLAN_INFO_PVID)); It is intuitive that the pvid of a netdevice should have the BRIDGE_VLAN_INFO_PVID flag set. However I can't seem to pinpoint a commit where this behavior was introduced. It seems like it's been like that since forever. At a first glance it would make more sense to just handle the BRIDGE_VLAN_INFO_PVID flag in __vlan_add_flags. However, as Nikolay explains: There are a few reasons why we don't do it, most importantly because we need to have only one visible pvid at any single time, even if it's stale - it must be just one. Right now that rule will not be violated by this change, but people will try using this flag and could see two pvids simultaneously. You can see that the pvid code is even using memory barriers to propagate the new value faster and everywhere the pvid is read only once. That is the reason the flag is set dynamically when dumping entries, too. A second (weaker) argument against would be given the above we don't want another way to do the same thing, specifically if it can provide us with two pvids (e.g. if walking the vlan list) or if it can provide us with a pvid different from the one set in the vg. [Obviously, I'm talking about RCU pvid/vlan use cases similar to the dumps. The locked cases are fine. I would like to avoid explaining why this shouldn't be relied upon without locking] So instead of introducing the above change and making sure of the pvid uniqueness under RCU, simply dynamically populate the pvid flag in br_vlan_get_info(). Signed-off-by: Vladimir Oltean <olteanv@gmail.com> Acked-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com> Signed-off-by: David S. Miller <davem@davemloft.net> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.