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.
A basic Floppy Disk Controller device driver for any system later than (and including) the IBM AT. The driver is based on the documentation supplied by QEMU, which is the datasheet for the Intel 82078 Floppy Disk controller (found here: https://wiki.qemu.org/images/f/f0/29047403.pdf)
Naturally, floppy disks are a _very_ outdated storage medium, however, as Serenity is a throwback to aesthetic 90s computing, it's a definite must have. Not to mention that there are still a lot of floppy disks around, with countless petabytes of software on them, so it would be nice if people could create images of said disks with serenity.
The code for this is mostly clean. however there are a LOT of values specified in the datasheet, so some of them might be wrong, not to mention that the actual specification itself is rather dirt and seemingly hacked together.
I'm also only supporting 3.5" floppy disks, without PIO polling (DMA only), so if you want anything more/less than 1.44MB HD Floppys, you'll have to do it yourself.
And use dbgprintf() consistently on a few of the pieces of logging here.
This is useful when trying to track thread switching when you don't
really care about what it's switching _to_.
Exec doesn't leave through the syscall handler, so it didn't unlock the
big_lock. This means that reentering can lock it again, and then another
thread could endlessly yield waiting to acquire the lock (futilely).
This fixes AudioServer using 100% CPU.
Currently this will be used by the WindowServer to show some dialogs.
This is needed since WindowServer can't use LibGUI and reimplementing
message box functionality inside WindowServer would be silly. :^)
The only dialog supported in this initial version is --shutdown
We were locking the list of references, and then destroying the
reference, which made things go a little crazy.
It's more straightforward to just remove the per-reference lock: the
syscalls all have to lock the full list anyway, so let's just do that
and avoid the hassle.
While I'm at it, also move the SharedBuffer code out to its own file as it's
getting a little long and unwieldly, and Process.cpp is already huge.
I was messing around with this to tell the compiler that these functions
always return the same value no matter how many times you call them.
It doesn't really seem to improve code generation and it looks weird so
let's just get rid of it.
