On 01/16/2015 08:16 PM, Greg Kroah-Hartman wrote: > 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. I tend to think that much of the above should also be part of the documentation file (patch 01/13). Cheers, Michael > 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 > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-api" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo 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