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David S. Miller 73bf1fc58d Merge branch 'net-ipv6-Fix-route-append-and-replace-use-cases' 
David Ahern says:

====================
net/ipv6: Fix route append and replace use cases

This patch set fixes a few append and replace uses cases for IPv6 and
adds test cases that codifies the expectations of how append and replace
are expected to work. In paricular it allows a multipath route to have
a dev-only nexthop, something Thomas tried to accomplish with commit
edd7ceb782 ("ipv6: Allow non-gateway ECMP for IPv6") which had to be
reverted because of breakage, and to replace an existing FIB entry
with a reject route.

There are a number of inconsistent and surprising aspects to the Linux
API for adding, deleting, replacing and changing FIB entries. For example,
with IPv4 NLM_F_APPEND means insert the route after any existing entries
with the same key (prefix + priority + TOS for IPv4) and NLM_F_CREATE
without the append flag inserts the new route before any existing entries.

IPv6 on the other hand attempts to guess whether a new route should be
appended to an existing one, possibly creating a multipath route, or to
add a new entry after any existing ones. This applies to both the 'append'
(NLM_F_CREATE + NLM_F_APPEND) and 'prepend' (NLM_F_CREATE only) cases
meaning for IPv6 the NLM_F_APPEND is basically ignored. This guessing
whether the route should be added to a multipath route (gateway routes)
or inserted after existing entries (non-gateway based routes) means a
multipath route can not have a dev only nexthop (potentially required in
some cases - tunnels or VRF route leaking for example) and route 'replace'
is a bit adhoc treating gateway based routes and dev-only / reject routes
differently.

This has led to frustration with developers working on routing suites
such as FRR where workarounds such as delete and add are used instead of
replace.

After this patch set there are 2 differences between IPv4 and IPv6:
1. 'ip ro prepend' = NLM_F_CREATE only
    IPv4 adds the new route before any existing ones
    IPv6 adds new route after any existing ones

2. 'ip ro append' = NLM_F_CREATE|NLM_F_APPEND
   IPv4 adds the new route after any existing ones
   IPv6 adds the nexthop to existing routes converting to multipath

For the former, there are cases where we want same prefix routes added
after existing ones (e.g., multicast, prefix routes for macvlan when used
for virtual router redundancy). Requiring the APPEND flag to add a new
route to an existing one helps here but is a slight change in behavior
since prepend with gateway routes now create a separate entry.

For the latter IPv6 behavior is preferred - appending a route for the same
prefix and metric to make a multipath route, so really IPv4 not allowing an
existing route to be updated is the limiter. This will be fixed when
nexthops become separate objects - a future patch set.

Thank you to Thomas and Ido for testing earlier versions of this set, and
to Ido for providing an update to the mlxsw driver.

Changes since RFC
- cleanup wording in test script; add comments about expected failures
  and why
====================

Signed-off-by: David S. Miller <davem@davemloft.net>
2018-05-22 14:44:20 -04:00
arch Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-05-21 16:01:54 -04:00
block blk-mq: fix sysfs inflight counter 2018-04-26 09:02:01 -06:00
certs certs/blacklist_nohashes.c: fix const confusion in certs blacklist 2018-02-21 15:35:43 -08:00
crypto crypto: drbg - set freed buffers to NULL 2018-04-21 00:57:00 +08:00
Documentation Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-05-21 16:01:54 -04:00
drivers mlxsw: spectrum_router: Add support for route append 2018-05-22 14:44:18 -04:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-05-21 16:01:54 -04:00
include net/ipv6: Simplify route replace and appending into multipath route 2018-05-22 14:44:18 -04:00
init Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-05-21 16:01:54 -04:00
ipc ipc/shm: fix use-after-free of shm file via remap_file_pages() 2018-04-13 17:10:27 -07:00
kernel Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-05-21 16:01:54 -04:00
lib Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-05-21 16:01:54 -04:00
LICENSES LICENSES: Add MPL-1.1 license 2018-01-06 10:59:44 -07:00
mm mmap: relax file size limit for regular files 2018-05-19 09:29:11 -07:00
net net/ipv6: Simplify route replace and appending into multipath route 2018-05-22 14:44:18 -04:00
samples Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-05-21 16:01:54 -04:00
scripts Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-05-21 16:01:54 -04:00
security Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-05-21 16:01:54 -04:00
sound ALSA: usb-audio: Use Class Specific EP for UAC3 devices. 2018-05-15 07:29:10 +02:00
tools selftests: fib_tests: Add ipv4 route add append replace tests 2018-05-22 14:44:19 -04:00
usr kbuild: rename built-in.o to built-in.a 2018-03-26 02:01:19 +09:00
virt KVM: arm/arm64: VGIC/ITS save/restore: protect kvm_read_guest() calls 2018-05-15 13:36:53 +02:00
.clang-format clang-format: add configuration file 2018-04-11 10:28:35 -07:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap Merge candidates for 4.17 merge window 2018-04-06 17:35:43 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS/CREDITS: Drop METAG ARCHITECTURE 2018-03-05 16:34:24 +00:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-05-21 16:01:54 -04:00
Makefile Linux 4.17-rc6 2018-05-20 15:31:38 -07:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -06:00

README 

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.
See Documentation/00-INDEX for a list of what is contained in each file.

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.