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bus: PORTING-DBUS1 clarify pool size value

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This commit is contained in:
Kay Sievers 2013-12-27 04:08:53 +01:00
parent 061eab675e
commit 0a6de11527
1 changed files with 12 additions and 14 deletions
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src/libsystemd-bus/PORTING-DBUS1
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@ -3,19 +3,19 @@ A few hints on supporting kdbus as backend in your favorite D-Bus library.
~~~
Before you read this, have a look at the DIFFERENCES and
GVARIANT_SERIALIZATION texts, you find in the same directory where you
GVARIANT_SERIALIZATION texts you find in the same directory where you
found this.
We invite you to port your favorite D-Bus protocol implementation
over to kdbus. However, there are a couple of complexities
involved. On kdbus we only speak GVariant marshaling, kdbus clients
ignore traffic in dbus1 marshaling. Thus, you need to add a second,
GVariant compatible marshaler to your libary first.
GVariant compatible marshaler to your library first.
After you have done that: here's the basic principle how kdbus works:
You connect to a bus by opening its bus node in /dev/kdbus/. All
buses have a device node there, that starts with a numeric UID of the
buses have a device node there, it starts with a numeric UID of the
owner of the bus, followed by a dash and a string identifying the
bus. The system bus is thus called /dev/kdbus/0-system, and for user
buses the device node is /dev/kdbus/1000-user (if 1000 is your user
@ -27,13 +27,13 @@ is a rough overview to help you grok things.)
CONNECTING
To connect to a bus, simply open() its device node, and issue the
To connect to a bus, simply open() its device node and issue the
KDBUS_CMD_HELLO call. That's it. Now you are connected. Do not send
Hello messages or so (as you would on dbus1), that does not exist for
kdbus.
The structure you pass to the ioctl will contain a couple of
parameters that you need to know to operate on the bus.
parameters that you need to know, to operate on the bus.
There are two flags fields, one indicating features of the kdbus
kernel side ("conn_flags"), the other one ("bus_flags") indicating
@ -54,7 +54,7 @@ communicating with the bus, however a client that does not support an
"incompatible" feature must not proceed with the connection.
The hello structure also contains another flags field "attach_flags"
which indicates meta data that is optionally attached to all incoming
which indicates metadata that is optionally attached to all incoming
messages. You probably want to set KDBUS_ATTACH_NAMES unconditionally
in it. This has the effect that all well-known names of a sender are
attached to all incoming messages. You need this information to
@ -71,12 +71,10 @@ broadcast bloom filter (see below).
The kernel will also return the bus ID of the bus in an 128bit field.
The pool size field specifies the size of the memory mapped buffer,
where received messages are placed by the kernel.
The pool size field specifies the size of the memory mapped buffer.
After the calling the hello ioctl, you should memory map the kdbus
fd. Use the pool size returned by the hello ioctl as map size. In this
memory mapped region the kernel will place all your incoming messages.
fd. In this memory mapped region, the kernel will place all your incoming
messages.
SENDING MESSAGES
@ -200,7 +198,7 @@ not used. Instead, you will only find PAYLOAD_OFF and PAYLOAD_MEMFD
items. The former contain an offset and size into your memory mapped
pool where you find the payload.
If during the HELLO ioctl you asked for getting meta data attached to
If during the HELLO ioctl you asked for getting metadata attached to
your message, you will find additional KDBUS_ITEM_CREDS,
KDBUS_ITEM_PID_COMM, KDBUS_ITEM_TID_COMM, KDBUS_ITEM_TIMESTAMP,
KDBUS_ITEM_EXE, KDBUS_ITEM_CMDLINE, KDBUS_ITEM_CGROUP,
@ -237,7 +235,7 @@ The bloom filter that needs to be included has the parameters m=512
(bits in the filter), k=8 (nr of hash functions). The underlying hash
function is SipHash-2-4. We calculate two hash values for an input
strings, one with the hash key b9660bf0467047c18875c49c54b9bd15 (this
is supposed to be read as a series of 16 hexadecimially formatted
is supposed to be read as a series of 16 hexadecimal formatted
bytes), and one with the hash key
aaa154a2e0714b39bfe1dd2e9fc54a3b. This results in two 64bit hash
values, A and B. The 8 hash functions for the bloom filter require a 9
@ -431,7 +429,7 @@ More specifically:
When a method call fails because the peer terminated the connection
before responding, a KDBUS_ITEM_REPLY_DEAD message is
generated. Simiarly, it should be synthesized into a method error
generated. Similarly, it should be synthesized into a method error
reply message.
For synthesized messages we recommend setting the cookie field to