Boolean arithmetic is great, use it!
if (a && !b)
return 1;
if (!a && b)
return -1,
is equivalent to
if (a != b)
return a - b;
Furthermore:
r = false;
if (condition)
r = true;
is equivalent to:
r = condition;
sd_device_new_from_* now returns -ENODEV when the device does not exist, and the enumerator
silently drops these errors as missing devices is exepected.
It is still possible to include uninitialized ones, but now that is opt-in. In most
cases people only want initialized devices. Exception is if you want to work without
udev running.
Suggested by David Herrmann.
We are talking about one member of a group of things (resource limits, signals,
timeouts), without specifying which one. An indenfinite article is in order.
When we are talking about the control process, it's a specific one, so the
definite article is used.
Whenever we provide a bus API that allows clients to create and manage
server-side objects, we need to provide a unique name for these objects.
There are two ways to provide them:
1) Let the server choose a name and return it as method reply.
2) Let the client pass its name of choice in the method arguments.
The first method is the easiest one to implement. However, it suffers from
a race condition: If a client creates an object asynchronously, it cannot
destroy that object until it received the method reply. It cannot know the
name of the new object, thus, it cannot destroy it. Furthermore, this
method enforces a round-trip. If the client _depends_ on the method call
to succeed (eg., it would close() the connection if it failed), the client
usually has no reason to wait for the method reply. Instead, the client
can immediately schedule further method calls on the newly created object
(in case the API guarantees in-order method-call handling).
The second method fixes both problems: The client passes an object name
with the method-call. The server uses it to create the object. Therefore,
the client can schedule object destruction even if the object-creation
hasn't finished, yet (again, requiring in-order method-call handling).
Furthermore, the client can schedule further method calls on the newly
created object, before the constructor returned.
There're two problems to solve, though:
1) Object names are usually defined via dbus object paths, which are
usually globally namespaced. Therefore, multiple clients must be able
to choose unique object names without interference.
2) If multiple libraries share the same bus connection, they must be
able to choose unique object names without interference.
The first problem is solved easily by prefixing a name with the
unique-bus-name of a connection. The server side must enforce this and
reject any other name.
The second problem is solved by providing unique suffixes from within
sd-bus. As long as sd-bus always returns a fresh new ID, if requested,
multiple libraries will never interfere. This implementation re-uses
bus->cookie as ID generator, which already provides unique IDs for each
bus connection.
This patch introduces two new helpers:
bus_path_encode_unique(sd_bus *bus,
const char *prefix,
const char *sender_id,
const char *external_id,
char **ret_path);
This creates a new object-path via the template
'/prefix/sender_id/external_id'. That is, it appends two new labels to
the given prefix. If 'sender_id' is NULL, it will use
bus->unique_name, if 'external_id' is NULL, it will allocate a fresh,
unique cookie from bus->cookie.
bus_path_decode_unique(const char *path,
const char *prefix,
char **ret_sender,
char **ret_external);
This reverses what bus_path_encode_unique() did. It parses 'path' from
the template '/prefix/sender/external' and returns both suffix-labels
in 'ret_sender' and 'ret_external'. In case the template does not
match, 0 is returned and both output arguments are set to NULL.
Otherwise, 1 is returned and the output arguments contain the decoded
labels.
Note: Client-side allocated IDs are inspired by the Wayland protocol
(which itself was inspired by X11). Wayland uses those IDs heavily
to avoid round-trips. Clients can create server-side objects and
send method calls without any round-trip and waiting for any object
IDs to be returned. But unlike Wayland, DBus uses gobally namespaced
object names. Therefore, we have to add the extra step by adding the
unique-name of the bus connection.
Users might have hard time figuring out why exactly their systemctl request
failed. If dbus job fails try to figure out more details about failure by
examining Result property of the service.
https://bugzilla.redhat.com/show_bug.cgi?id=1016680
Avoid unbound for(;;) loop and use the established coding-style:
while ((r = sd_bus_message_read*(...)) > 0) {
}
if (r < 0)
return r;
This is much easier to read and used all over the code base.
If necessary the passed string is enclosed in "", and all special
characters escapes.
This also ports over usage in bus-util.c and job.c to use this, instead
of a incorrect local implementation that forgets to properly escape.
Interactive authorization should only happen asynchronously, hence
disallow it in synchronous bus_verify_polkit(), and rename it to
bus_test_polkit(). This way even if the bus message header asks for
interactive authorization, we'll ask for non-interactive authorization
which is actually the desired behaviour if CanSuspend, CanHibernate and
friends, which call this function.
Change cunescape() to return a normal error code, so that we can
distuingish OOM errors from parse errors.
This also adds a flags parameter to control whether "relaxed" or normal
parsing shall be done. If set no parse failures are generated, and the
only reason why cunescape() can fail is OOM.
I shall not use alloca() within loops
I shall not use alloca() within loops
I shall not use alloca() within loops
I shall not use alloca() within loops
...
This provides equivalent functionality to libudev-device, but in the
systemd style. The public API only caters to creating sd_device objects
from for devices that already exist in /sys, there is no support for
listening for monitoring events or creating devices received over
the udev netlink protocol.
The private API contains the necessary functionality to make sd-device
a drop-in replacement for libudev-device, but which we would not
otherwise want to export.
like:
src/shared/install.c: In function ‘unit_file_lookup_state’:
src/shared/install.c:1861:16: warning: ‘r’ may be used uninitialized in
this function [-Wmaybe-uninitialized]
return r < 0 ? r : state;
^
src/shared/install.c:1796:13: note: ‘r’ was declared here
int r;
^
We strips out NLMSG_DONE piece from a multi-part message adding into the
receive queue only the messages containing actual data.
If we send a request to the kernel for getting the forwarding database table (just an example),
the response will be a multi-part message like below:
1. FDB entry 1;
2. FDB entry 2;
3. NLMSG_DONE;
We strip out "3. NLMSG_DONE;" part and places into the receive queue a pointer to
"1. FDB entry 1; 2. FDB entry 2".
But if the FDB table is empty, the respose from the kernel will look like below:
1. NLMSG_DONE;
We strip out "1. NLMSG_DONE;" part and since there is no actual data got, it continues
waiting until reaching timeout.
Therefore, a call to "sd_rtnl_call" to send and wait for a response from kernel will exit
with timeout which is interpreted as error in communication.
This patch puts the NLMSG_DONE message on the receive queue if it ends an empty multi-part
message. This situation is detected in sd_rtnl_call() and in the callback code and NULL is
returned to the caller instead.
[tomegun:
- added/reworded commit message
- extend the same support to sd_rtnl_call_async()
- drop debug logging from library, we only do this if something is really wrong, but an
empty multi-part message is perfectly normal
- modernize the code we touch whilst we are at it]
Coverity was complaining that CMSG_NXTHDR is used without
checking the return value. In this case it cannot fail, but
it is a good excuse to simplify the function a bit.
CID #1261726.
