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This is the current list of things I want to fix before I consider UML
to have reached version 1.
<p>
I've attached a description to each one which will provide some
guidance as to proceed with it. If you need more details, contact me
or send mail off to the uml-devel list.
<p>
<ul>
<li>
<b>
<p>
My attempts to run the Debian install procedure hung UML while it was
probing disks. I never figured out what was happening.
</b>
<p>
If someone verifies that UML can run a Debian installation, I'll
consider this fixed.
</li>
<p>
<li>
<b>
<p>
Make UML build without warnings
</b>
<p>
I've been knocking these off one by one. The remaining ones are
mostly cries for reorganization. There are pieces of userspace code
in kernel files which call libc functions without there being
declarations in scope. Mostly, these things need to be separated from
whatever kernel code they're in, and moved to a userspace file.
<p>
An exception to this is the pair of warnings from kernel/timer.c. I'm
going to fix this by bumping UML's HZ to 50.
<p>
Remember the errno redefinition warning in user_syms.c during the deb build.
</li>
<p>
<li>
<b>
<p>
Make sure that each clock tick gets counted
</b>
<p>
If you run UML under load for a while, you'll notice that clock ticks
are being missed. You can see this by doing a 'ps uax' every once in
a while, and noticing that process start times are moving. I made an
attempt to fix this by never having SIGVTALRM or SIGALRM blocked and
doing some fancy flag checking to make sure that the IRQ handler is
only called if it's safe, and otherwise just bumping a count of missed
ticks. The next time it's safe, the IRQ handler will be called once
for the current tick and once for each previously missed tick,
catching the system up with the real time.
<p>
This doesn't fix it for some reason. The only reason I can think of
is that the signals are getting stacked because a second one comes in
before the first one has been collected by the handler. I have a hard
time believing that the host can be so bogged down that it can't call
the signal handler within 1/HZ seconds of the alarm happening. The
signal is going through the tracing thread courtesy of ptrace, so
maybe that's introducing enough delay to stack the signals.
</li>
<p>
<p>
<li>
<b>
<p>
Figure out the hostfs crash that Larent Bonnaud is seeing
</b>
<p>
Laurent hasn't complained about this recently. If he doesn't, I'll
just consider this fixed.
</li>
<p>
<li>
<b>
<p>
make 'gdb=pty' work
</b>
<p>
Run UML with 'debug gdb=pty' on the command line, attach to whatever
pty gdb gets, and you'll see the problem. There's some major problem
with the terminal modes that I've never figured out.
</li>
<p>
<li>
<b>
<p>
protect kernel memory from userspace
</b>
<p>
Fixing this will make it impossible for a nasty UML user to escape
from UML and execute arbitrary system calls on the host. It has four
pieces:
<ul>
<li>
Write-protect kernel physical and virtual memory whenever UML is in
userspace. The exception to this is the process kernel stack, which
needs to be writable in order for a signal handler to be run on it.
This is OK because whatever the process puts there will just be
overwritten by the signal handler. This is partially implemented -
kernel physical memory is protected, except for the four pages making
up the task structure and stack. Protecting the task structure is
complicated because there is some UML code which effectively runs in
userspace which calls the process signal handler to deliver signals.
It needs to be able to write to the task structure. I think this fix
is to move that code to before the signal starts being delivered,
which will involve redoing parts of the signal delivery code.
Protecting kernel virtual memory is a matter of walking the kernel
page tables and write-protecting everything that's mapped there.
</li>
<li>
Locating and disabling all drivers that provide access to kernel
memory through interfaces such as /proc/kcore.
</li>
<li>
Fixing the access_ok macro so it rejects any attempt to fake the
kernel into changing its own memory by passing a kernel address as an
argument to a system call.
</li>
<li>
In the host kernel, adding a new personality which segfaults any
attempt to execute a SysV system call. These are not traced by
ptrace, so a process that knows how to use them is not jailed inside UML.
</li>
</ul>
</li>
<p>
<li>
<b>
<p>
Figure out why the io_thread loses its parent and its connection to the kernel
</b>
<p>
This happened once, a long time ago. The system hung because the IO
thread lost its connection to UML somehow. I haven't seen it since,
so this will probably be considered fixed.
</li>
<p>
<li>
<b>
<p>
Get either Myrtal Meep or Matt Clay
to confirm (or not) that they can no longer crash UML with
Apache/Perl/MySQL. This will probably be fixed with the new network drivers.
</b>
<p>
The new network drivers probably fixed these problems. This will be
considered fixed unless people start complaining about it again.
</li>
<p>
<li>
<b>
<p>
I have an old bug that claims that UML can be crashed with a ping
flood. I haven't seen this happen recently, so if anyone else has,
you'd better let me know.
</b>
<p>
This is probably fixed. I do ping floods fairly regularly and haven't
seen any problems.
</li>
<p>
<li>
<b>
<p>
Disable SIGIO on file descriptors which are already being handled.
This will cut off some interrupt recursion.
</b>
<p>
This is an efficiency thing and stack depth precaution. We don't want
sigio_handler to run recursively on the same descriptor because the
descriptor will be handled at the top level.
</li>
<p>
<li>
<b>
<p>
Figure out why gdb can't use fd chan (blinky@gmx.net)
</b>
<p>
One of the ioctls that sets up the terminal for gdb returns EPERM.
</li>
<p>
<li>
<b>
<p>
Figure out why repeated 'tail /dev/zero' with swap causes process segfaults
</b>
<p>
I stopped being able to reproduce this, so it might be considered
mysteriously fixed at some point.
</li>
<p>
<li>
<b>
<p>
The ptrace proxy should handle wait correctly for non-UML subprocesses of gdb
</b>
<p>
Shelling out of the kernel debugger will cause a hang. That's because
the ptrace proxy is not prepared for a real wait for a real child to
happen.
</li>
<p>
<li>
<b>
<p>
Set SA_RESTART on SIGPROF
</b>
<p>
This will prevent SIGPROF from causing system calls on the host from
returning EINTR and messing things up inside UML.
</li>
<p>
<li>
<b>
<p>
Allow registration of sockets for panics and console output
</b>
<p>
This involves some work on the mconsole client side to support making
the requests and work in UML to add the mconsole notification to the
panic_notify_chain and to somehow get console output to the client.
My best idea on doing this is to add support for multiple channels on
consoles and support for write-only channels. Then the mconsole
client can stack a write-only channel to a socket or something on top
of whatever channel is already there.
</li>
<p>
<li>
<b>
<p>
Replace dentry_name with d_name
</b>
<p>
Cleanup - I implemented dentry_name, not knowing about d_name, which
does the same thing. One problem might be that dentry_name expects
the file to exist, which might cause something to break when d_name
returns a '/foo/bar/baz (deleted)' name.
</li>
<p>
<li>
<b>
<p>
Bind a UML unix socket to a host unix socket
</b>
<p>
This is a cute feature which would involve passing something like
'hostsock=/tmp/.X11-unix/X0,X' on the command line, which would cause
the hostsock driver to create a /proc/hostsock/X unix socket inside
UML and pass all operations and data on it through to the host's
/tmp/.X11-unix/X0. Then, you'd create /tmp/.X11-unix/X0 in UML as a
link to /proc/hostsock/X and be able to run X clients on the host X
server without needing the network up.
</li>
<p>
<li>
<b>
<p>
Dynamically allocate all driver descriptors
</b>
<p>
The static arrays in the drivers should go away and be replaced by
dynamically allocated buffers, maybe in a list. This will turn
lookups of particular devices into O(N) operations, but maybe that's
OK. Also, the transport arrays in the various transports should
similarly go away.
</li>
<p>
<li>
<b>
<p>
Make slip_tramp conditional in slip_close
</b>
<p>
slip_open doesn't always invoke the helper through slip_tramp, so
slip_close similarly shouldn't.
</li>
<p>
<li>
<b>
<p>
Implement thread_saved_pc
</b>
<p>
This is an unimplemented piece of the SysRq support.
</li>
<p>
<li>
<b>
<p>
many du / causes slab cache corruption
</b>
<p>
This wasn't entirely reproducable, but I did see a couple cases of
panics with slab corruption when running a lot of du's. I fixed the
process segfault problem, and this problem has probably disappeared as
well.
</li>
<p>
<li>
<b>
<p>
ddd doesn't work with gdb-pid
</b>
<p>
ddd seems to be doing something strange wrt gdb. When 'att 1' is done,
gdb just dies and becomes a zombie. What's happening is that ddd,
which is the parent of gdb, is calling wait. When UML attaches to
gdb, it becomes the new parent, and ddd starts getting ECHILD instead
of 0. It closes down the pipe it shares with gdb, and gdb sees EOF on
it, and exits.
</li>
<p>
<li>
<b>
<p>
Adding an eth device via the mconsole (and probably the command line)
won't necessarily configure the device that was named
</b>
<p>
The kernel does its own ordering of devices, so configuring eth1 without
configuring eth0 gives you eth0.
</li>
<p>
<li>
<b>
<p>
Figure out why running a properly built UML under UML doesn't work
</b>
<p>
</li>
<p>
<li>
<b>
<p>
Allow a COW file to change its backing file with
'ubdx=cow-file,new-backing-file'
</b>
<p>
This assigns some potentially useful semantics to a syntax that is
currently meaningless. Currently, the backing-file argument is
ignored for an already-existing COW file.
</li>
<p>
<li>
<b>
<p>Implement /proc/umid
</b>
<p>
This would let UML be configured on the inside with knowledge of what
instance it is.
</li>
<p>
<li>
<b>
<p>
Figure out why leaning on the space bar when top is running causes an FPE.
</b>
<p>
I'm suspicious that this is caused by UML not saving floating point
state when it enters the kernel and somehow munging the process
floating point registers.
</li>
<p>
<li>
<b>
<p>
Fix the ubd rounding bug spotted by Steve Schmidtke and Roman Zippel.
</b>
<p>
If the number of sectors isn't a multiple of 8, then the bitmap will
be a a byte shorter than it should be.
</li>
<p>
<li>
<b>
<p>
gdb should be the last thing to be shut down so that breakpoints can
be set late in the shutdown process.
</b>
<p>
</li>
<p>
<li>
<b>
<p>
Have the __uml_exitcall handlers check to see if they need to do anything.
</b>
<p>
If UML is ^C-ed before things are set up, then the cleanup handlers are
cleaning up after things which were never initialized.
</li>
<p>
<li>
<b>
<p>
Using strace as an external debugger doesn't work. strace sees no system
calls starting at the delay calibration.
</b>
<p>
</li>
<p>
<li>
<b>
<p>
Find the race that causes the kernel to run before the debugger is running,
and which then causes a panic and segfault.
</b>
<p>
</li>
<p>
<li>
<b>
<p>
mconsole clients need to pass absolute pathnames into UML.
</b>
<p>
</li>
<p>
<li>
<b>
<p>
Tests that need writing
<ul>
<li>
Build and load some modules to check for unexported symbols
</li>
<li>
Swap testing - qsbench, low-memory kernel build
</li>
<li>
Rerun some existing tests through hostfs
</li>
</ul>
</b>
<p>
</li>
<p>
<li>
<b>
<p>
Get the tracing thread out of the business of running trampolines
</b>
<p>
</li>
<p>
<li>
<b>
<p>
Figure out why gdb inside UML sometimes misses breakpoints.
</b>
<p>
</li>
<p>
<li>
<b>
<p>
close_chan should call free_irq, not free_irq_by_fd
</b>
<p>
</li>
<p>
<li>
<b>
<p>
Look at the initrd dependencies. UML doesn't compile when initrd support
is disabled.
</b>
<p>
</li>
<p>
<li>
<b>
<p>
Multiple opens of a pty console cause irq registrations to pile up.
</b>
<p>
</li>
<p>
<li>
<b>
<p>
The uml_net entry points should check their argcs.
</b>
<p>
</li>
<p>
<li>
<b>
<p>
Figure out why large pastes into consoles get truncated.
</b>
<p>
</li>
<p>
<li>
<b>
<p>
'next' across a statement which segfaults causes wait_for_stop to get
confused by the segfault.
</b>
<p>
</li>
<p>
</ul>
</td>
</tr>
</table>
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