The syscall is quite simple:
int watch_file(const char* path, int path_length);
It returns a file descriptor referring to a "InodeWatcher" object in the
kernel. It becomes readable whenever something changes about the inode.
Currently this is implemented by hooking the "metadata dirty bit" in
Inode which isn't perfect, but it's a start. :^)
The "stddbg" stream was a cute idea but we never ended up using it in
practice, so let's simplify this and implement userspace dbgprintf() on top
of a simple dbgputch() syscall instead.
This makes debugging LibC startup a little bit easier. :^)
Restructure the makefile a little so it only builds objects once, and
then run them on make clean.
This is a little slower (since we're relinking tests each makeall), but
it also ensures that it will work.
With the presence of signal handlers, it is possible that a thread might
be blocked multiple times. Picture for instance a signal handler using
read(), or wait() while the thread is already blocked elsewhere before
the handler is invoked.
To fix this, we turn m_blocker into a chain of handlers. Each block()
call now prepends to the list, and unblocking will only consider the
most recent (first) blocker in the chain.
Fixes#309
This is very simple but already very useful. Now you're able to call to
dump_backtrace() from anywhere userspace to get a nice symbolicated
backtrace in the debugger output. :^)
The only two places we set m_blocker now are Thread::set_state(), and
Thread::block(). set_state is mostly just an issue of clarity: we don't
want to end up with state() != Blocked with an m_blocker, because that's
weird. It's also possible: if we yield, someone else may set_state() us.
We also now set_state() and set m_blocker under lock in block(), rather
than unlocking which might allow someone else to mess with our internals
while we're in the process of trying to block.
This seems to fix sending STOP & CONT causing a panic.
My guess as to what was happening is this:
thread A blocks in select(): Blocking & m_blocker != nullptr
thread B sends SIGSTOP: Stopped & m_blocker != nullptr
thread B sends SIGCONT: we continue execution. Runnable & m_blocker != nullptr
thread A tries to block in select() again:
* sets m_blocker
* unlocks (in block_helper)
* someone else tries to unblock us? maybe from the old m_blocker? unclear -- clears m_blocker
* sets Blocked (while unlocked!)
So, thread A is left with state Blocked & m_blocker == nullptr, leading
to the scheduler assert (m_blocker != nullptr) failing.
Long story short, let's do all our data management with the lock _held_.
And use this to return EINTR in various places; some of which we were
not handling properly before.
This might expose a few bugs in userspace, but should be more compatible
with other POSIX systems, and is certainly a little cleaner.
I had the right cause of the SharedBuffer leak, but goofed the fix by
desynching the per-pid refcount and the global refcount.
Fix that, and add a generous sprinkle of asserts to make sure the two
stay in sync.
Fixes#341
(... for real this time)
It's a very bad idea to increment the refcount on behalf of another
process. That process may (for either benign or evil reasons) not
reference the SharedBuffer, and then we'll be stuck with loads of
SharedBuffers until we OOM.
Instead, increment the refcount when the buffer is mapped. That way, a
buffer is only kept if *someone* has explicitly requested it via
get_shared_buffer.
Fixes#341
Generate a special page containing the "return from signal" trampoline code
on startup and then route signalled threads to it. This avoids a page
allocation in every process that ever receives a signal.
Region now has is_user_accessible(), which informs the memory manager how
to map these pages. Previously, we were just passing a "bool user_allowed"
to various functions and I'm not at all sure that any of that was correct.
All the Region constructors are now hidden, and you must go through one of
these helpers to construct a region:
- Region::create_user_accessible(...)
- Region::create_kernel_only(...)
That ensures that we don't accidentally create a Region without specifying
user accessibility. :^)
And use it in the scheduler.
IntrusiveList is similar to InlineLinkedList, except that rather than
making assertions about the type (and requiring inheritance), it
provides an IntrusiveListNode type that can be used to put an instance
into many different lists at once.
As a proof of concept, port the scheduler over to use it. The only
downside here is that the "list" global needs to know the position of
the IntrusiveListNode member, so we have to position things a little
awkwardly to make that happen. We also move the runnable lists to
Thread, to avoid having to publicize the node.
Committing some things my hands did while browsing through this code.
- Mark all leaf classes "final".
- FileDescriptionBlocker now stores a NonnullRefPtr<FileDescription>.
- FileDescriptionBlocker::blocked_description() now returns a reference.
- ConditionBlocker takes a Function&&.
"Blocking" is not terribly informative, but now that everything is
ported over, we can force the blocker to provide us with a reason.
This does mean that to_string(State) needed to become a member, but
that's OK.
Rolling with the theme of adding a dialog to shutdown the machine, it is
probably nice to have a way to reboot the machine without performing a full
system powerdown.
A reboot program has been added to `/bin/` as well as a corresponding
`syscall` (SC_reboot). This syscall works by attempting to pulse the 8042
keyboard controller. Note that this is NOT supported on new machines, and
should only be a fallback until we have proper ACPI support.
The implementation causes a triple fault in QEMU, which then restarts the
system. The filesystems are locked and synchronized before this occurs,
so there shouldn't be any corruption etctera.
BXVGADevice was using a Size object for its framebuffer size. We shouldn't
be pulling in userspace code in the kernel like this, even if it's just
headers. :^)
Instead of LibGUI and WindowServer building their own copies of the drawing
and graphics code, let's it in a separate LibDraw library.
This avoids building the code twice, and will encourage better separation
of concerns. :^)
This allows us to seal a buffer *before* anyone else has access to it
(well, ok, the creating process still does, but you can't win them all).
It also means that a SharedBuffer can be shared with multiple clients:
all you need is to have access to it to share it on again.
