xchg is advertised as a bidirectional exchange dir, but file content
transfer from host to VM fails due to caching:
If a file is read in the VM and then modified on the host, subsequent
re-reads in the VM can yield old, cached data.
This is caused by the use of 9p's cache=loose mode that is explicitly
meant for read-only mounts.
9p doesn't provide any suitable cache modes, so fix this by disabling
caching.
Also, remove a now unnecessary sync in the test driver.
Whenever we create scripts that are installed to $out, we must use runtimeShell
in order to get the shell that can be executed on the machine we create the
package for. This is relevant for cross-compiling. The only use case for
stdenv.shell are scripts that are executed as part of the build system.
Usages in checkPhase are borderline however to decrease the likelyhood
of people copying the wrong examples, I decided to use runtimeShell as well.
The motivation for this change is the following: As gnu-netcat,
e. g. does not support ipv6, it is not suitable as default netcat.
This commit also fixes all obvious build issues caused by this change.
This seems to be the root cause of the random page allocation failures
and @wizeman did a very good job on not only finding the root problem
but also giving a detailed explanation of it in #10828.
Here is an excerpt:
The problem here is that the kernel is trying to allocate a contiguous
section of 2^7=128 pages, which is 512 KB. This is way too much:
kernel pages tend to get fragmented over time and kernel developers
often go to great lengths to try allocating at most only 1 contiguous
page at a time whenever they can.
From the error message, it looks like the culprit is unionfs, but this
is misleading: unionfs is the name of the userspace process that was
running when the system ran out of memory, but it wasn't unionfs who
was allocating the memory: it was the kernel; specifically it was the
v9fs_dir_readdir_dotl() function, which is the code for handling the
readdir() function in the 9p filesystem (the filesystem that is used
to share a directory structure between a qemu host and its VM).
If you look at the code, here's what it's doing at the moment it tries
to allocate memory:
buflen = fid->clnt->msize - P9_IOHDRSZ;
rdir = v9fs_alloc_rdir_buf(file, buflen);
If you look into v9fs_alloc_rdir_buf(), you will see that it will try
to allocate a contiguous buffer of memory (using kzalloc(), which is a
wrapper around kmalloc()) of size buflen + 8 bytes or so.
So in reality, this code actually allocates a buffer of size
proportional to fid->clnt->msize. What is this msize? If you follow
the definition of the structures, you will see that it's the
negotiated buffer transfer size between 9p client and 9p server. On
the client side, it can be controlled with the msize mount option.
What this all means is that, the reason for running out of memory is
that the code (which we can't easily change) tries to allocate a
contiguous buffer of size more or less equal to "negotiated 9p
protocol buffer size", which seems to be way too big (in our NixOS
tests, at least).
After that initial finding, @lethalman tested the gnome3 gdm test
without setting the msize parameter at all and it seems to have resolved
the problem.
The reason why I'm committing this without testing against all of the
NixOS VM test is basically that I think we can only go better but not
worse than the current state.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
This ensures that the intermediate machine is shut down only after the
migration has finished writing the memory dump to disk, to ensure we
don't end up with empty state files depending on how fast the migration
finished before we actually shut down the VM.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
This ensures that the builder isn't waiting forever if the Windows VM
drops dead while we're waiting for the controller VM to signal that a
particular command has been executed on the Windows VM. It won't ever
happen in such cases so it doesn't make sense to wait for the timeout.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
So far, the VMs have always been using the native architecture, because
it was reimporting <nixpkgs> several times. Now, we propagate a list of
packages down to all sub-imports, which not only makes clearer which
dependencies a part actually has, but also will make it easier in case
we want to refactor those parts to use callPackage.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
This is the last item that was missing to get a fully working
runInWindowsVM function. Apart from checking exit codes, we also now
have preVM/postVM hooks which we can use to write arbitrary constructs
around this architecture, without the need to worry about specific
details.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
Later, when we start the actual builder, we're going to restore those
environment variables. We're using "(set; declare -p)", here, because
the former is just printing _all_ environment variables, even those not
supported, and the latter only lists specifically declared variables,
which also encludes exports.
The "declare -p" command also emits those variables in a format similar
to the "export" command.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
We now map all guest accounts to the root user, because in the end the
permissions of the current user boil down to the build user of the Nix
builder of the host. That way it's not possible to gain more permissions
at all and just makes the VM communication a lot easier.
However, setting "writable" to yes instead of "read only" to no doesn't
change anything here, I just found it to be clearer.
Also, we now no longer need to have a "nobody" user.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
This is done by putting the non-initrd /nix/store into a subdirectory,
which we then chroot to and pass along the SSH command.
Also, we now collect the exit code after the chroot command and power
off the VM thereafter, because the store is no longer shadowed and we
have still access to the busybox inside the initrd.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
This should trim down possible dependencies on the base installation and
hereby reduce the need for reinstallation of the damn VM to only changes
that affect the Windows installation and the base Cygwin + OpenSSH
setup.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
This now finally introduces our xchg share and also uses it for
exchanging state while suspending a VM. However, accessing the _real_
Nix store still isn't possible because we're shadowing the directory in
the initrd.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
Security-wise it's not a big issue because we're still sandboxed, but I
really don't want to write something like \\\\\\\\192.168.0.2\\\\share
in order to set up network shares.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
This could possibly cause flapping whenever qemu is too fast in starting
up. As we are running with the shell's -e flag, the socat check also
ensures that the VDE switch is properly started and causes the whole
build to fail, should it not start up within 20 seconds.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
These stages are in particular:
* Install of the bare Windows VM with Cygwin and shut down.
* Boot up the same VM again without the installation media and dump the
VMs memory to state.gz.
* Resume from state.gz and build whatever we want to build.
Every single stage involves a new "controller", which is more like an
abstraction on the Nix side that constructs the madness described in
276b72fb93.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
