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Before this commit bus messages had a single reference count: when it
reached zero the message would be freed. This simple approach meant a
cyclic dependency was typically seen: a message that was enqueued in a
bus connection object would reference the bus connection object but also
itself be referenced by the bus connection object. So far out strategy
to avoid cases like this was: make sure to process the bus connection
regularly so that messages don#t stay queued, and at exit flush/close
the connection so that the message queued would be emptied, and thus the
cyclic dependencies resolved. Im many cases this isn't done properly
however.
With this change, let's address the issue more systematically: let's
break the reference cycle. Specifically, there are now two types of
references to a bus message:
1. A regular one, which keeps both the message and the bus object it is
associated with pinned.
2. A "queue" reference, which is weaker: it pins the message, but not
the bus object it is associated with.
The idea is then that regular user handling uses regular references, but
when a message is enqueued on its connection, then this takes a "queue"
reference instead. This then means that a queued message doesn't imply
the connection itself remains pinned, only regular references to the
connection or a message associated with it do. Thus, if we end up in the
situation where a user allocates a bus and a message and enqueues the
latter in the former and drops all refs to both, then this will detect
this case and free both.
Note that this scheme isn't perfect, it only covers references between
messages and the busses they are associated with. If OTOH a bus message
is enqueued on a different bus than it is associated with cyclic deps
cannot be recognized with this simple algorithm, and thus if you enqueue
a message associated with a bus A on a bus B, and another message
associated with bus B on a bus A, a cyclic ref will be in effect and not
be discovered. However, given that this is an exotic case (though one
that happens, consider systemd-bus-stdio-bridge), it should be OK not to
cover with this, and people have to explicit flush all queues on exit in
that case.
Note that this commit only establishes the separate reference counters
per message. A follow-up commit will start making use of this from the
bus connection object.
Don't try to be smart, don't bypass the ref counting logic if there's no
real reason to.
This matters if we want to tweak the ref counting logic later.
Let's make sure our own code follows coding style and initializes all
return values on all types of success (and leaves it uninitialized in
all types of failure).
Let's do this like we usually do and size arrays with size_t.
We already do this for the "allocated" counter correctly, and externally
we expose the queue sizes as uint64_t anyway, hence there's really no
point in usigned "unsigned" internally.
We document and all our code assumes that LoaderDevicePartUUID is
initialized to the ESP's UUID. Let's hence not override the variable if
it is already set, in order to not confuse userspace if the kernel's EFI
image is run from a different partition than the ESP.
This matches behaviour for all other variables set by the EFI stub, in
particular the closely related LoaderImageIdentifier variable.
Our own variables are in the the "loader" GUID namespace, but our code
so far checked the "global" GUID namespace (i.e. EFI's own), before
setting the variables. Correct that, so that we always check the right
namespace for existing variables before we write them.
The specification always said so, let's actually implement this.
Unfortunately UEFI's own APIs don't allow us to search for partition
type GUID, hence we have to implement a minimal GPT parser ourselves.
In a follow-up commit we'd like to invoke config_entry_add_from_file()
on partitions that are not the ESP, let's prepare fpr that and allow
loaded_image_path to be passed as NULL.
This makes the code a bit simpler (after all the call is not interested
in the loaded image, just where it is found), and more like
config_load_entries() which takes the same arguments.
This also makes things easier for us later on, when we add support for
discovering images in $XBOOTLDR partitions.
Let's add a new function that checks whether some directory is the
top-level directory inside an fs, splitting out the code for this from
verify_esp().
While we are at it, let's slightly improve the code, so that we can
correctly work if we have no priviliges but the ESP is mounted
unaccessible: if we can't stat() the path "$ESP/.." then manually remove
the last component of $ESP and check that instead. Which is very similar
in behaviour, and hopefully good enough in the unprivileged case.
udev metadata access works unprivileged, which the blkid stuff doesn't
(as that needs raw device node access). Hence let's use udev if we lack
privs, and raw device access only if root.
This 'root' field contains the root path of the partition we found the
snippet in. The 'kernel', 'initrd', 'efi', … fields are relative to this
path.
This becomes particularly useful later when we add support for loading
snippets from both the ESP and XBOOTLDR, but already simplifies the code
for us a bit in systemctl.
Previously, we'd mount the ESP to /efi if that existed and was empty,
falling back to /boot if that existed and was empty.
With this change, the XBOOTLDR partition is mounted to /boot
unconditionally. And the EFI is mounted to /efi if that exists (but it
doesn't have to be empty — after all the name is very indicative of what
this is supposed to be), and to /boot as a fallback but only if it
exists and is empty (we insist on emptiness for that, since it might be
used differently than what we assume).
The net effect is that $BOOT should be reliably found under /boot, and
the ESP is either /efi or /boot.
(Note that this commit only is relevant for nspawn and suchlike, i.e.
the codepaths that mount an image without involving udev during boot.)
The boot loader spec supports two places to store boot loader
configuration: the ESP and a generic replacement for it in case the ESP
is not available or not suitable. Let's look for both.
