From Greg Kroah-Hartman <> Subject [PATCH v3 00/13] Add kdbus implementation Date Fri, 16 Jan 2015 11:16:04 -0800 kdbus is a kernel-level IPC implementation that aims for resemblance to

the the protocol layer with the existing userspace D-Bus daemon while

enabling some features that couldn't be implemented before in userspace.



The documentation in the first patch in this series explains the

protocol and the API details.



Full details on what has changed from the v2 submission are at the

bottom of this email.



Reasons why this should be done in the kernel, instead of userspace as

it is currently done today include the following:



- performance: fewer process context switches, fewer copies, fewer

syscalls, larger memory chunks via memfd. This is really important

for a whole class of userspace programs that are ported from other

operating systems that are run on tiny ARM systems that rely on

hundreds of thousands of messages passed at boot time, and at

"critical" times in their user interaction loops.

- security: the peers which communicate do not have to trust each other,

as the only trustworthy compoenent in the game is the kernel which

adds metadata and ensures that all data passed as payload is either

copied or sealed, so that the receiver can parse the data without

having to protect against changing memory while parsing buffers. Also,

all the data transfer is controlled by the kernel, so that LSMs can

track and control what is going on, without involving userspace.

Because of the LSM issue, security people are much happier with this

model than the current scheme of having to hook into dbus to mediate

things.

- more metadata can be attached to messages than in userspace

- semantics for apps with heavy data payloads (media apps, for instance)

with optinal priority message dequeuing, and global message ordering.

Some "crazy" people are playing with using kdbus for audio data in the

system. I'm not saying that this is the best model for this, but

until now, there wasn't any other way to do this without having to

create custom "busses", one for each application library.

- being in the kernle closes a lot of races which can't be fixed with

the current userspace solutions. For example, with kdbus, there is a

way a client can disconnect from a bus, but do so only if no further

messages present in its queue, which is crucial for implementing

race-free "exit-on-idle" services

- eavesdropping on the kernel level, so privileged users can hook into

the message stream without hacking support for that into their

userspace processes

- a number of smaller benefits: for example kdbus learned a way to peek

full messages without dequeing them, which is really useful for

logging metadata when handling bus-activation requests.



Of course, some of the bits above could be implemented in userspace

alone, for example with more sophisticated memory management APIs, but

this is usually done by losing out on the other details. For example,

for many of the memory management APIs, it's hard to not require the

communicating peers to fully trust each other. And we _really_ don't

want peers to have to trust each other.



Another benefit of having this in the kernel, rather than as a userspace

daemon, is that you can now easily use the bus from the initrd, or up to

the very end when the system shuts down. On current userspace D-Bus,

this is not really possible, as this requires passing the bus instance

around between initrd and the "real" system. Such a transition of all

fds also requires keeping full state of what has already been read from

the connection fds. kdbus makes this much simpler, as we can change the

ownership of the bus, just by passing one fd over from one part to the

other.



Regarding binder: binder and kdbus follow very different design

concepts. Binder implies the use of thread-pools to dispatch incoming

method calls. This is a very efficient scheme, and completely natural

in programming languages like Java. On most Linux programs, however,

there's a much stronger focus on central poll() loops that dispatch all

sources a program cares about. kdbus is much more usable in such

environments, as it doesn't enforce a threading model, and it is happy

with serialized dispatching. In fact, this major difference had an

effect on much of the design decisions: binder does not guarantee global

message ordering due to the parallel dispatching in the thread-pools,

but kdbus does. Moreover, there's also a difference in the way message

handling. In kdbus, every message is basically taken and dispatched as

one blob, while in binder, continious connections to other peers are

created, which are then used to send messages on. Hence, the models are

quite different, and they serve different needs. I believe that the

D-Bus/kdbus model is more compatible and friendly with how Linux

programs are usually implemented.



This can also be found in a git tree, the kdbus branch of char-misc.git at:

https://git.kernel.org/cgit/linux/kernel/git/gregkh/char-misc.git/



Changes since v2:



* Add FS_USERNS_MOUNT to the file system flags, so users can mount

their own kdbusfs instances without being root in the parent

user-ns. Spotted by Andy Lutomirski.



* Rewrite major parts of the metadata implementation to allow for

per-recipient namespace translations. For this, namespaces are

now not pinned by domains anymore. Instead, metadata is recorded

in kernel scope, and exported into the currently active namespaces

at the time of message installing.



* Split PID and TID from KDBUS_ITEM_CREDS into KDBUS_ITEM_PIDS.

The starttime is there to detect re-used PIDs, so move it to that

new item type as well. Consequently, introduce struct kdbus_pids

to accommodate the information. Requested by Andy Lutomirski.



* Add {e,s,fs}{u,g}id to KDBUS_ITEM_CREDS, so users have a way to

get more fine-grained credential information.



* Removed KDBUS_CMD_CANCEL. The interface was not usable from

threaded userspace implementation due to inherent races. Instead,

add an item type CANCEL_FD which can be used to pass a file

descriptor to the CMD_SEND ioctl. When the SEND is done

synchronously, it will get cancelled as soon as the passed

FD signals POLLIN.



* Dropped startttime from KDBUS_ITEM_PIDS



* Restrict names of custom endpoints to names with a "<uid>-" prefix,

just like we do for buses.



* Provide module-parameter "kdbus.attach_flags_mask" to specify the

a mask of metadata items that is applied on all exported items.



* Monitors are now entirely invisible (IOW, there won't be any

notification when they are created) and they don't need to install

filters for broadcast messages anymore.



* All information exposed via a connection's pool now also reports

the length in addition to the offset. That way, userspace

applications can mmap() only parts of the pool on demand.



* Due to the metadata rework, KDBUS_ITEM_PAYLOAD_OFF items now

describe the offset relative to the pool, where they used to be

relative to the message header.



* Added return_flags bitmask to all kdbus_cmd_* structs, so the

kernel can report details of the command processing. This is

mostly reserved for future extensions.



* Some fixes in kdbus.txt and tests, spotted by Harald Hoyer, Andy

Lutomirski, Michele Curti, Sergei Zviagintsev, Sheng Yong, Torstein

Husebø and Hristo Venev.



* Fixed compiler warnings in test-message by Michele Curti



* Unexpected items are now rejected with -EINVAL



* Split signal and broadcast handling. Unicast signals are now

supported, and messages have a new KDBUS_MSG_SIGNAL flag.



* KDBUS_CMD_MSG_SEND was renamed to KDBUS_CMD_SEND, and now takes

a struct kdbus_cmd_send instead of a kdbus_msg.



* KDBUS_CMD_MSG_RECV was renamed to KDBUS_CMD_RECV.



* Test case memory leak plugged, and various other cleanups and

fixes, by Rui Miguel Silva.



* Build fix for s390



* Test case fix for 32bit archs



* The test framework now supports mount, pid and user namespaces.



* The test framework learned a --tap command line parameter to

format its output in the "Test Anything Protocol". This format

is chosen by default when "make kselftest" is invoked.



* Fixed buses and custom endpoints name validation, reported by

Andy Lutomirski.



* copy_from_user() return code issue fixed, reported by

Dan Carpenter.



* Avoid signed int overflow on archs without atomic_sub



* Avoid variable size stack items. Fixes a sparse warning in queue.c.



* New test case for kernel notification quota



* Switched back to enums for the list of ioctls. This has advantages

for userspace code as gdb, for instance, is able to resolve the

numbers into names. Added features can easily be detected with

autotools, and new iotcls can get #defines as well. Having #defines

for the initial set of ioctls is uncecessary.



Daniel Mack (13):

kdbus: add documentation

kdbus: add header file

kdbus: add driver skeleton, ioctl entry points and utility functions

kdbus: add connection pool implementation

kdbus: add connection, queue handling and message validation code

kdbus: add node and filesystem implementation

kdbus: add code to gather metadata

kdbus: add code for notifications and matches

kdbus: add code for buses, domains and endpoints

kdbus: add name registry implementation

kdbus: add policy database implementation

kdbus: add Makefile, Kconfig and MAINTAINERS entry

kdbus: add selftests



Documentation/ioctl/ioctl-number.txt | 1 +

Documentation/kdbus.txt | 2107 +++++++++++++++++++++

MAINTAINERS | 12 +

include/uapi/linux/Kbuild | 1 +

include/uapi/linux/kdbus.h | 1049 ++++++++++

include/uapi/linux/magic.h | 2 +

init/Kconfig | 12 +

ipc/Makefile | 2 +-

ipc/kdbus/Makefile | 22 +

ipc/kdbus/bus.c | 553 ++++++

ipc/kdbus/bus.h | 103 +

ipc/kdbus/connection.c | 2004 ++++++++++++++++++++

ipc/kdbus/connection.h | 262 +++

ipc/kdbus/domain.c | 350 ++++

ipc/kdbus/domain.h | 84 +

ipc/kdbus/endpoint.c | 232 +++

ipc/kdbus/endpoint.h | 68 +

ipc/kdbus/fs.c | 519 +++++

ipc/kdbus/fs.h | 25 +

ipc/kdbus/handle.c | 1134 +++++++++++

ipc/kdbus/handle.h | 20 +

ipc/kdbus/item.c | 309 +++

ipc/kdbus/item.h | 57 +

ipc/kdbus/limits.h | 95 +

ipc/kdbus/main.c | 72 +

ipc/kdbus/match.c | 535 ++++++

ipc/kdbus/match.h | 32 +

ipc/kdbus/message.c | 598 ++++++

ipc/kdbus/message.h | 133 ++

ipc/kdbus/metadata.c | 1066 +++++++++++

ipc/kdbus/metadata.h | 52 +

ipc/kdbus/names.c | 891 +++++++++

ipc/kdbus/names.h | 82 +

ipc/kdbus/node.c | 910 +++++++++

ipc/kdbus/node.h | 87 +

ipc/kdbus/notify.c | 244 +++

ipc/kdbus/notify.h | 30 +

ipc/kdbus/policy.c | 481 +++++

ipc/kdbus/policy.h | 51 +

ipc/kdbus/pool.c | 784 ++++++++

ipc/kdbus/pool.h | 47 +

ipc/kdbus/queue.c | 505 +++++

ipc/kdbus/queue.h | 108 ++

ipc/kdbus/reply.c | 262 +++

ipc/kdbus/reply.h | 68 +

ipc/kdbus/util.c | 317 ++++

ipc/kdbus/util.h | 133 ++

tools/testing/selftests/Makefile | 1 +

tools/testing/selftests/kdbus/.gitignore | 11 +

tools/testing/selftests/kdbus/Makefile | 46 +

tools/testing/selftests/kdbus/kdbus-enum.c | 95 +

tools/testing/selftests/kdbus/kdbus-enum.h | 14 +

tools/testing/selftests/kdbus/kdbus-test.c | 920 +++++++++

tools/testing/selftests/kdbus/kdbus-test.h | 85 +

tools/testing/selftests/kdbus/kdbus-util.c | 1646 ++++++++++++++++

tools/testing/selftests/kdbus/kdbus-util.h | 216 +++

tools/testing/selftests/kdbus/test-activator.c | 319 ++++

tools/testing/selftests/kdbus/test-attach-flags.c | 751 ++++++++

tools/testing/selftests/kdbus/test-benchmark.c | 427 +++++

tools/testing/selftests/kdbus/test-bus.c | 174 ++

tools/testing/selftests/kdbus/test-chat.c | 123 ++

tools/testing/selftests/kdbus/test-connection.c | 611 ++++++

tools/testing/selftests/kdbus/test-daemon.c | 66 +

tools/testing/selftests/kdbus/test-endpoint.c | 344 ++++

tools/testing/selftests/kdbus/test-fd.c | 710 +++++++

tools/testing/selftests/kdbus/test-free.c | 36 +

tools/testing/selftests/kdbus/test-match.c | 442 +++++

tools/testing/selftests/kdbus/test-message.c | 658 +++++++

tools/testing/selftests/kdbus/test-metadata-ns.c | 507 +++++

tools/testing/selftests/kdbus/test-monitor.c | 158 ++

tools/testing/selftests/kdbus/test-names.c | 184 ++

tools/testing/selftests/kdbus/test-policy-ns.c | 633 +++++++

tools/testing/selftests/kdbus/test-policy-priv.c | 1270 +++++++++++++

tools/testing/selftests/kdbus/test-policy.c | 81 +

tools/testing/selftests/kdbus/test-race.c | 313 +++

tools/testing/selftests/kdbus/test-sync.c | 368 ++++

tools/testing/selftests/kdbus/test-timeout.c | 99 +

77 files changed, 27818 insertions(+), 1 deletion(-)

create mode 100644 Documentation/kdbus.txt

create mode 100644 include/uapi/linux/kdbus.h

create mode 100644 ipc/kdbus/Makefile

create mode 100644 ipc/kdbus/bus.c

create mode 100644 ipc/kdbus/bus.h

create mode 100644 ipc/kdbus/connection.c

create mode 100644 ipc/kdbus/connection.h

create mode 100644 ipc/kdbus/domain.c

create mode 100644 ipc/kdbus/domain.h

create mode 100644 ipc/kdbus/endpoint.c

create mode 100644 ipc/kdbus/endpoint.h

create mode 100644 ipc/kdbus/fs.c

create mode 100644 ipc/kdbus/fs.h

create mode 100644 ipc/kdbus/handle.c

create mode 100644 ipc/kdbus/handle.h

create mode 100644 ipc/kdbus/item.c

create mode 100644 ipc/kdbus/item.h

create mode 100644 ipc/kdbus/limits.h

create mode 100644 ipc/kdbus/main.c

create mode 100644 ipc/kdbus/match.c

create mode 100644 ipc/kdbus/match.h

create mode 100644 ipc/kdbus/message.c

create mode 100644 ipc/kdbus/message.h

create mode 100644 ipc/kdbus/metadata.c

create mode 100644 ipc/kdbus/metadata.h

create mode 100644 ipc/kdbus/names.c

create mode 100644 ipc/kdbus/names.h

create mode 100644 ipc/kdbus/node.c

create mode 100644 ipc/kdbus/node.h

create mode 100644 ipc/kdbus/notify.c

create mode 100644 ipc/kdbus/notify.h

create mode 100644 ipc/kdbus/policy.c

create mode 100644 ipc/kdbus/policy.h

create mode 100644 ipc/kdbus/pool.c

create mode 100644 ipc/kdbus/pool.h

create mode 100644 ipc/kdbus/queue.c

create mode 100644 ipc/kdbus/queue.h

create mode 100644 ipc/kdbus/reply.c

create mode 100644 ipc/kdbus/reply.h

create mode 100644 ipc/kdbus/util.c

create mode 100644 ipc/kdbus/util.h

create mode 100644 tools/testing/selftests/kdbus/.gitignore

create mode 100644 tools/testing/selftests/kdbus/Makefile

create mode 100644 tools/testing/selftests/kdbus/kdbus-enum.c

create mode 100644 tools/testing/selftests/kdbus/kdbus-enum.h

create mode 100644 tools/testing/selftests/kdbus/kdbus-test.c

create mode 100644 tools/testing/selftests/kdbus/kdbus-test.h

create mode 100644 tools/testing/selftests/kdbus/kdbus-util.c

create mode 100644 tools/testing/selftests/kdbus/kdbus-util.h

create mode 100644 tools/testing/selftests/kdbus/test-activator.c

create mode 100644 tools/testing/selftests/kdbus/test-attach-flags.c

create mode 100644 tools/testing/selftests/kdbus/test-benchmark.c

create mode 100644 tools/testing/selftests/kdbus/test-bus.c

create mode 100644 tools/testing/selftests/kdbus/test-chat.c

create mode 100644 tools/testing/selftests/kdbus/test-connection.c

create mode 100644 tools/testing/selftests/kdbus/test-daemon.c

create mode 100644 tools/testing/selftests/kdbus/test-endpoint.c

create mode 100644 tools/testing/selftests/kdbus/test-fd.c

create mode 100644 tools/testing/selftests/kdbus/test-free.c

create mode 100644 tools/testing/selftests/kdbus/test-match.c

create mode 100644 tools/testing/selftests/kdbus/test-message.c

create mode 100644 tools/testing/selftests/kdbus/test-metadata-ns.c

create mode 100644 tools/testing/selftests/kdbus/test-monitor.c

create mode 100644 tools/testing/selftests/kdbus/test-names.c

create mode 100644 tools/testing/selftests/kdbus/test-policy-ns.c

create mode 100644 tools/testing/selftests/kdbus/test-policy-priv.c

create mode 100644 tools/testing/selftests/kdbus/test-policy.c

create mode 100644 tools/testing/selftests/kdbus/test-race.c

create mode 100644 tools/testing/selftests/kdbus/test-sync.c

create mode 100644 tools/testing/selftests/kdbus/test-timeout.c









