async def _make_local_thread() -> Thread:
"""Create the local thread, allocating various resources locally.
For the most part, the local thread is like any other thread; it just bootstraps
differently, and uses syscall and memory interfaces which are specialized to the local
thread.
"""
process = near.Process(os.getpid())
task = Task(
LocalSyscall(),
process,
far.FDTable(process.id),
far.AddressSpace(process.id),
far.PidNamespace(process.id),
)
ram = RAM(task, LocalMemoryTransport(task),
memory.AllocatorClient.make_allocator(task))
epfd = await task.epoll_create()
async def wait_readable():
logger.debug("wait_readable(%s)", epfd.near.number)
await trio.hazmat.wait_readable(epfd.near.number)
epoller = Epoller.make_subsidiary(ram, epfd, wait_readable)
thread = Thread(
task,
ram,
await FDPassConnection.make(task, ram, epoller),
NativeLoader.make_from_symbols(task, lib),
epoller,
await ChildProcessMonitor.make(ram, task, epoller),
Environment(task, ram, {
key.encode(): value.encode()
for key, value in os.environ.items()
}),
stdin=task.make_fd_handle(near.FileDescriptor(0)),
stdout=task.make_fd_handle(near.FileDescriptor(1)),
stderr=task.make_fd_handle(near.FileDescriptor(2)),
)
return thread
async def _make_local_process() -> Process:
"""Create the local process, allocating various resources locally.
For the most part, the local process is like any other process; it just bootstraps
differently, and uses syscall and memory interfaces which are specialized to the local
process.
"""
pid = near.Pid(os.getpid())
task = Task(
pid,
handle.FDTable(pid.id),
far.AddressSpace(pid.id),
far.PidNamespace(pid.id),
far.MountNamespace(pid.id),
)
task.sysif = LocalSyscall(task)
task.allocator = await memory.AllocatorClient.make_allocator(task)
epfd = await task.epoll_create()
async def wait_readable():
logger.debug("wait_readable(%s)", epfd.near.number)
await trio.lowlevel.wait_readable(epfd.near.number)
trio_system_wait_readable = TrioSystemWaitReadable(epfd.near.number)
set_trio_system_wait_readable(trio_system_wait_readable)
epoller = Epoller.make_subsidiary(epfd, trio_system_wait_readable.wait)
process = Process(
task,
await FDPassConnection.make(task, epoller),
NativeLoader.make_from_symbols(task, lib),
epoller,
await ChildPidMonitor.make(task, epoller),
Environment.make_from_environ(task, {**os.environ}),
stdin=task.make_fd_handle(near.FileDescriptor(0)),
stdout=task.make_fd_handle(near.FileDescriptor(1)),
stderr=task.make_fd_handle(near.FileDescriptor(2)),
)
return process
async def launch_futex_monitor(
loader: NativeLoader, monitor: ChildPidMonitor,
futex_pointer: WrittenPointer[FutexNode]) -> AsyncChildPid:
"""Launch a process to wait on a futex; then we monitor the process to monitor the futex
This process calls futex(futex_pointer, FUTEX_WAIT, futex_pointer.value) and
then exits, so this process will exit if and when the futex has FUTEX_WAKE
called on it.
Sadly, this is the best we can do with integrating futexes into our event
loop. There used to be a way to get a file descriptor to represent a futex,
but it was removed because it was racy.
Something better would be really great - especially because it would allow
incorporating pprocesss locks and other shared memory concurrency mechanisms
based on futexes, into a normal event loop.
"""
stack_value = loader.make_trampoline_stack(
Trampoline(loader.futex_helper_func, [
int(futex_pointer.near +
ffi.offsetof('struct futex_node', 'futex')),
futex_pointer.value.futex
]))
stack_buf = await monitor.cloning_task.malloc(Stack, 4096)
stack = await stack_buf.write_to_end(stack_value, alignment=16)
futex_pid = await monitor.clone(CLONE.VM | CLONE.FILES, stack)
# wait for futex helper to SIGSTOP itself,
# which indicates the trampoline is done and we can deallocate the stack.
state = await futex_pid.waitpid(W.EXITED | W.STOPPED)
if state.state(W.EXITED):
raise Exception(
"process internal futex-waiting task died unexpectedly", state)
# resume the futex_process so it can start waiting on the futex
await futex_pid.kill(SIG.CONT)
# TODO uh we need to actually call something to free the stack
return futex_pid
async def stdin_bootstrap(
parent: Thread,
bootstrap_command: Command,
) -> t.Tuple[AsyncChildProcess, Thread]:
"""Create a thread from running an arbitrary command which must run rsyscall-stdin-bootstrap
bootstrap_command can be any arbitrary command, but it must eventually exec
rsyscall-stdin-bootstrap, and pass down stdin when it does.
We'll fork and exec bootstrap_command, passing down a socketpair for stdin, and try to
bootstrap over the other end of the socketpair. Once rsyscall-stdin-bootstrap starts,
it will respond to our bootstrap and we'll create a new thread.
"""
#### fork and exec into the bootstrap command
child = await parent.fork()
# create the socketpair that will be used as stdin
stdin_pair = await (await parent.task.socketpair(
AF.UNIX, SOCK.STREAM, 0, await parent.ram.malloc(Socketpair))).read()
parent_sock = stdin_pair.first
child_sock = stdin_pair.second.move(child.task)
# set up stdin with socketpair
await child.unshare_files(going_to_exec=True)
await child.stdin.replace_with(child_sock)
# exec
child_process = await child.exec(bootstrap_command)
#### set up all the fds we'll want to pass over
# the basic connections
[(access_syscall_sock, passed_syscall_sock),
(access_data_sock, passed_data_sock)] = await parent.open_async_channels(2)
# memfd for setting up the futex
futex_memfd = await parent.task.memfd_create(
await parent.ram.ptr(Path("child_robust_futex_list")))
# send the fds to the new process
connection_fd, make_connection = await parent.connection.prep_fd_transfer()
async def sendmsg_op(sem: RAM) -> WrittenPointer[SendMsghdr]:
iovec = await sem.ptr(IovecList([await sem.malloc(bytes, 1)]))
cmsgs = await sem.ptr(CmsgList([CmsgSCMRights([
passed_syscall_sock, passed_data_sock, futex_memfd, connection_fd])]))
return await sem.ptr(SendMsghdr(None, iovec, cmsgs))
_, [] = await parent_sock.sendmsg(await parent.ram.perform_batch(sendmsg_op), SendmsgFlags.NONE)
# close our reference to fds that only the new process needs
await passed_syscall_sock.close()
await passed_data_sock.close()
# close the socketpair
await parent_sock.close()
#### read describe to get all the information we need from the new process
describe_buf = AsyncReadBuffer(access_data_sock)
describe_struct = await describe_buf.read_cffi('struct rsyscall_stdin_bootstrap')
environ = await describe_buf.read_envp(describe_struct.envp_count)
#### build the new task
pid = describe_struct.pid
fd_table = far.FDTable(pid)
address_space = far.AddressSpace(pid)
# we assume pid namespace is shared
# TODO include namespace inode numbers numbers in describe
# note: if we start dealing with namespace numbers then we need to
# have a Kernel namespace which tells us which kernel we get those
# numbers from.
# oh hey we can conveniently dump the inode numbers with getdents!
pidns = parent.task.pidns
process = near.Process(pid)
remote_syscall_fd = near.FileDescriptor(describe_struct.syscall_fd)
syscall = NonChildSyscallInterface(SyscallConnection(access_syscall_sock, access_syscall_sock), process)
base_task = Task(syscall, process, fd_table, address_space, pidns)
handle_remote_syscall_fd = base_task.make_fd_handle(remote_syscall_fd)
syscall.store_remote_side_handles(handle_remote_syscall_fd, handle_remote_syscall_fd)
allocator = memory.AllocatorClient.make_allocator(base_task)
# we assume our SignalMask is zero'd before being started, so we don't inherit it
ram = RAM(base_task,
SocketMemoryTransport(access_data_sock,
base_task.make_fd_handle(near.FileDescriptor(describe_struct.data_fd)),
allocator),
allocator)
# TODO I think I can maybe elide creating this epollcenter and instead inherit it or share it, maybe?
epoller = await Epoller.make_root(ram, base_task)
child_monitor = await ChildProcessMonitor.make(ram, base_task, epoller)
connection = make_connection(base_task, ram,
base_task.make_fd_handle(near.FileDescriptor(describe_struct.connecting_fd)))
new_parent = Thread(
task=base_task,
ram=ram,
connection=connection,
loader=NativeLoader.make_from_symbols(base_task, describe_struct.symbols),
epoller=epoller,
child_monitor=child_monitor,
environ=Environment(base_task, ram, environ),
stdin=base_task.make_fd_handle(near.FileDescriptor(0)),
stdout=base_task.make_fd_handle(near.FileDescriptor(1)),
stderr=base_task.make_fd_handle(near.FileDescriptor(2)),
)
#### TODO set up futex I guess
remote_futex_memfd = near.FileDescriptor(describe_struct.futex_memfd)
return child_process, new_parent
async def ssh_bootstrap(
parent: Process,
# the actual ssh command to run
ssh_command: SSHCommand,
# the local path we'll use for the socket
local_socket_path: Path,
# the directory we're bootstrapping out of
tmp_path_bytes: bytes,
) -> t.Tuple[AsyncChildPid, Process]:
"Over ssh, run the bootstrap executable, "
# identify local path
local_data_addr = await parent.ram.ptr(
await SockaddrUn.from_path(parent, local_socket_path))
# start port forwarding; we'll just leak this process, no big deal
# TODO we shouldn't leak processes; we should be GCing processes at some point
forward_child_pid = await ssh_forward(
parent, ssh_command, local_socket_path, (tmp_path_bytes + b"/data").decode())
# start bootstrap
bootstrap_process = await parent.fork()
bootstrap_child_pid = await bootstrap_process.exec(ssh_command.args(
"-n", f"cd {tmp_path_bytes.decode()}; exec ./bootstrap rsyscall"
))
# TODO should unlink the bootstrap after I'm done execing.
# it would be better if sh supported fexecve, then I could unlink it before I exec...
# Connect to local socket 4 times
async def make_async_connection() -> AsyncFileDescriptor:
sock = await parent.make_afd(await parent.socket(AF.UNIX, SOCK.STREAM|SOCK.NONBLOCK))
await sock.connect(local_data_addr)
return sock
async_local_syscall_sock = await make_async_connection()
async_local_data_sock = await make_async_connection()
# Read description off of the data sock
describe_buf = AsyncReadBuffer(async_local_data_sock)
describe_struct = await describe_buf.read_cffi('struct rsyscall_bootstrap')
new_pid = describe_struct.pid
environ = await describe_buf.read_envp(describe_struct.envp_count)
# Build the new task!
new_address_space = far.AddressSpace(new_pid)
# TODO the pid namespace will probably be common for all connections...
# TODO we should get this from the SSHHost, this is usually going
# to be common for all connections and we should express that
new_pid_namespace = far.PidNamespace(new_pid)
new_pid = near.Pid(new_pid)
new_base_task = Task(
new_pid, handle.FDTable(new_pid), new_address_space,
new_pid_namespace,
)
handle_remote_syscall_fd = new_base_task.make_fd_handle(near.FileDescriptor(describe_struct.syscall_sock))
new_base_task.sysif = SyscallConnection(
logger.getChild(str(new_pid)),
async_local_syscall_sock, async_local_syscall_sock,
handle_remote_syscall_fd, handle_remote_syscall_fd,
)
handle_remote_data_fd = new_base_task.make_fd_handle(near.FileDescriptor(describe_struct.data_sock))
handle_listening_fd = new_base_task.make_fd_handle(near.FileDescriptor(describe_struct.listening_sock))
new_allocator = memory.AllocatorClient.make_allocator(new_base_task)
new_transport = SocketMemoryTransport(async_local_data_sock, handle_remote_data_fd)
# we don't inherit SignalMask; we assume ssh zeroes the sigmask before starting us
new_ram = RAM(new_base_task, new_transport, new_allocator)
epoller = await Epoller.make_root(new_ram, new_base_task)
child_monitor = await ChildPidMonitor.make(new_ram, new_base_task, epoller)
await handle_listening_fd.fcntl(F.SETFL, O.NONBLOCK)
connection = ListeningConnection(
parent.task, parent.ram, parent.epoller,
local_data_addr,
new_base_task, new_ram,
await AsyncFileDescriptor.make(epoller, new_ram, handle_listening_fd),
)
new_process = Process(
task=new_base_task,
ram=new_ram,
connection=connection,
loader=NativeLoader.make_from_symbols(new_base_task, describe_struct.symbols),
epoller=epoller,
child_monitor=child_monitor,
environ=Environment.make_from_environ(new_base_task, new_ram, environ),
stdin=new_base_task.make_fd_handle(near.FileDescriptor(0)),
stdout=new_base_task.make_fd_handle(near.FileDescriptor(1)),
stderr=new_base_task.make_fd_handle(near.FileDescriptor(2)),
)
return bootstrap_child_pid, new_process
async def rsyscall_exec(
parent: Thread,
child: ChildThread,
executable: RsyscallServerExecutable,
) -> None:
"""exec rsyscall-server and repair the thread to continue working after the exec
This is of fairly limited use except as a stress-test for our primitives.
We need to know about our parent thread because we need to create a new futex child
process to wait for the child calling exec. We can't have the child itself create this
futex process because the whole point of the futex process is to monitor for the child
calling exec or exit; see ChildSyscallInterface. That futex process can be a child of
anyone, so technically `parent` doesn't have to be our parent, it just needs to
currently share its fd table with us.
For the new futex process, we need to use a robust futex, registered on the
robust_list. The robust_list is, unfortunately, the only truly robust way to get
notified of a process calling exec. We use ctid elsewhere, but the kernel has an
irritating check where it only does a futex wakeup on ctid if the process's memory
space is shared. The kernel always does the robust_list wakeups, so we can rely on the
robust list even when we're working with processes that don't share address space.
"""
[(access_data_sock, passed_data_sock)] = await child.open_async_channels(1)
# create this guy and pass him down to the new thread
child_futex_memfd = await child.task.memfd_create(await child.ram.ptr(
Path("child_robust_futex_list")))
parent_futex_memfd = child_futex_memfd.for_task(parent.task)
if isinstance(child.task.sysif, ChildSyscallInterface):
syscall = child.task.sysif
else:
raise Exception("can only exec in ChildSyscallInterface sysifs, not",
child.task.sysif)
# unshare files so we can unset cloexec on fds to inherit
await child.unshare_files(going_to_exec=True)
# unset cloexec on all the fds we want to copy to the new space
for fd in child.task.fd_handles:
await fd.fcntl(F.SETFD, 0)
def encode(fd: FileDescriptor) -> bytes:
return str(int(fd.near)).encode()
#### call exec and set up the new task
await child.exec(
executable.command.args(
encode(passed_data_sock),
encode(syscall.infd),
encode(syscall.outfd),
*[encode(fd) for fd in child.task.fd_handles],
), [child.monitor.sigfd.signal_block])
if len(syscall.rsyscall_connection.pending_responses) == 1:
# remove execve from pending_responses, we're never going to get a response to it
syscall.rsyscall_connection.pending_responses = []
else:
raise Exception(
"syscall connection in bad state; " +
"expected one pending response for execve, instead got",
syscall.rsyscall_connection.pending_responses)
# a new address space needs a new allocator and transport; we mutate the RAM so things
# that have stored the RAM continue to work.
child.ram.allocator = memory.AllocatorClient.make_allocator(child.task)
child.ram.transport = SocketMemoryTransport(access_data_sock,
passed_data_sock,
child.ram.allocator)
# rsyscall-server will write the symbol table to passed_data_sock, and we'll read it
# from access_data sock to set up the symbol table for the new address space
child.loader = NativeLoader.make_from_symbols(
child.task, await AsyncReadBuffer(access_data_sock).read_cffi(
'struct rsyscall_symbol_table'))
#### make new futex process
# The futex process we used before is dead now that we've exec'd. We need to make some
# syscalls in the child to set up the new futex process. ChildSyscallInterface would
# throw immediately on seeing the current dead futex_process, so we need to null it out.
syscall.futex_process = None
# We have to use a robust futex now for our futex_process, see docstring
parent_futex_ptr, child_futex_ptr = await setup_shared_memory_robust_futex(
parent, parent_futex_memfd, child, child_futex_memfd)
syscall.futex_process = await launch_futex_monitor(parent.ram,
parent.loader,
parent.monitor,
parent_futex_ptr)
# now we are alive and fully working again, we can be used for GC
child.task._add_to_active_fd_table_tasks()
async def _setup_stub(
thread: Thread,
bootstrap_sock: FileDescriptor,
) -> t.Tuple[t.List[str], Thread]:
"Setup a stub thread"
[(access_syscall_sock, passed_syscall_sock),
(access_data_sock, passed_data_sock)
] = await thread.open_async_channels(2)
# memfd for setting up the futex
futex_memfd = await thread.task.memfd_create(await thread.ram.ptr(
Path("child_robust_futex_list")))
# send the fds to the new process
connection_fd, make_connection = await thread.connection.prep_fd_transfer()
async def sendmsg_op(sem: RAM) -> WrittenPointer[SendMsghdr]:
iovec = await sem.ptr(IovecList([await sem.malloc(bytes, 1)]))
cmsgs = await sem.ptr(
CmsgList([
CmsgSCMRights([
passed_syscall_sock, passed_data_sock, futex_memfd,
connection_fd
])
]))
return await sem.ptr(SendMsghdr(None, iovec, cmsgs))
_, [] = await bootstrap_sock.sendmsg(
await thread.ram.perform_batch(sendmsg_op), SendmsgFlags.NONE)
# close our reference to fds that only the new process needs
await passed_syscall_sock.invalidate()
await passed_data_sock.invalidate()
# close the socketpair
await bootstrap_sock.invalidate()
#### read describe to get all the information we need from the new process
describe_buf = AsyncReadBuffer(access_data_sock)
describe_struct = await describe_buf.read_cffi('struct rsyscall_unix_stub')
argv_raw = await describe_buf.read_length_prefixed_array(
describe_struct.argc)
argv = [os.fsdecode(arg) for arg in argv_raw]
environ = await describe_buf.read_envp(describe_struct.envp_count)
#### build the new task
pid = describe_struct.pid
fd_table = handle.FDTable(pid)
address_space = far.AddressSpace(pid)
# we assume pid namespace is shared
pidns = thread.task.pidns
process = near.Process(pid)
# we assume net namespace is shared - that's dubious...
# we should make it possible to control the namespace sharing more, hmm.
# TODO maybe the describe should contain the net namespace number? and we can store our own as well?
# then we can automatically do it right
base_task = Task(process, fd_table, address_space, pidns)
remote_syscall_fd = base_task.make_fd_handle(
near.FileDescriptor(describe_struct.syscall_fd))
base_task.sysif = SyscallConnection(
logger.getChild(str(process)),
access_syscall_sock,
access_syscall_sock,
remote_syscall_fd,
remote_syscall_fd,
)
allocator = memory.AllocatorClient.make_allocator(base_task)
base_task.sigmask = Sigset(
{SIG(bit)
for bit in rsyscall.struct.bits(describe_struct.sigmask)})
ram = RAM(
base_task,
SocketMemoryTransport(
access_data_sock,
base_task.make_fd_handle(
near.FileDescriptor(describe_struct.data_fd))), allocator)
# TODO I think I can maybe elide creating this epollcenter and instead inherit it or share it, maybe?
# I guess I need to write out the set too in describe
epoller = await Epoller.make_root(ram, base_task)
child_monitor = await ChildProcessMonitor.make(ram, base_task, epoller)
connection = make_connection(
base_task, ram,
base_task.make_fd_handle(
near.FileDescriptor(describe_struct.connecting_fd)))
new_thread = Thread(
task=base_task,
ram=ram,
connection=connection,
loader=NativeLoader.make_from_symbols(base_task,
describe_struct.symbols),
epoller=epoller,
child_monitor=child_monitor,
environ=Environment.make_from_environ(base_task, ram, environ),
stdin=base_task.make_fd_handle(near.FileDescriptor(0)),
stdout=base_task.make_fd_handle(near.FileDescriptor(1)),
stderr=base_task.make_fd_handle(near.FileDescriptor(2)),
)
#### TODO set up futex I guess
remote_futex_memfd = near.FileDescriptor(describe_struct.futex_memfd)
return argv, new_thread
async def stdin_bootstrap(
parent: Process,
bootstrap_command: Command,
) -> t.Tuple[AsyncChildPid, Process]:
"""Create a process from running an arbitrary command which must run rsyscall-stdin-bootstrap
bootstrap_command can be any arbitrary command, but it must eventually exec
rsyscall-stdin-bootstrap, and pass down stdin when it does.
We'll clone and exec bootstrap_command, passing down a socketpair for stdin, and try to
bootstrap over the other end of the socketpair. Once rsyscall-stdin-bootstrap starts,
it will respond to our bootstrap and we'll create a new process.
"""
#### clone and exec into the bootstrap command
# create the socketpair that will be used as stdin
stdin_pair = await (await parent.task.socketpair(
AF.UNIX, SOCK.STREAM, 0, await parent.task.malloc(Socketpair))).read()
parent_sock = stdin_pair.first
child = await parent.fork()
# set up stdin with socketpair
await child.task.inherit_fd(stdin_pair.second).dup2(child.stdin)
await stdin_pair.second.close()
# exec
child_pid = await child.exec(bootstrap_command)
#### set up all the fds we'll want to pass over
# the basic connections
[(access_syscall_sock, passed_syscall_sock),
(access_data_sock, passed_data_sock)
] = await parent.open_async_channels(2)
# send the fds to the new process
connection_fd, make_connection = await parent.connection.prep_fd_transfer()
iovec = await parent.ptr(IovecList([await parent.malloc(bytes, 1)]))
cmsgs = await parent.ptr(
CmsgList([
CmsgSCMRights(
[passed_syscall_sock, passed_data_sock, connection_fd])
]))
_, [] = await parent_sock.sendmsg(
await parent.ptr(SendMsghdr(None, iovec, cmsgs)), SendmsgFlags.NONE)
# close our reference to fds that only the new process needs
await passed_syscall_sock.close()
await passed_data_sock.close()
# close the socketpair
await parent_sock.close()
#### read describe to get all the information we need from the new process
describe_buf = AsyncReadBuffer(access_data_sock)
describe_struct = await describe_buf.read_cffi(
'struct rsyscall_stdin_bootstrap')
environ = await describe_buf.read_envp(describe_struct.envp_count)
#### build the new task
pid = describe_struct.pid
fd_table = handle.FDTable(pid)
address_space = far.AddressSpace(pid)
# we assume pid namespace is shared
# TODO include namespace inode numbers numbers in describe
# note: if we start dealing with namespace numbers then we need to
# have a Kernel namespace which tells us which kernel we get those
# numbers from.
# oh hey we can conveniently dump the inode numbers with getdents!
pidns = parent.task.pidns
# we assume mount namespace is not shared (can't hurt)
mountns = far.MountNamespace(pid)
pid = near.Pid(pid)
base_task = Task(pid, fd_table, address_space, pidns, mountns)
remote_syscall_fd = base_task.make_fd_handle(
near.FileDescriptor(describe_struct.syscall_fd))
base_task.sysif = SyscallConnection(
logger.getChild(str(pid)),
access_syscall_sock,
remote_syscall_fd,
)
base_task.allocator = await memory.AllocatorClient.make_allocator(base_task
)
# we assume our SignalMask is zero'd before being started, so we don't inherit it
# TODO I think I can maybe elide creating this epollcenter and instead inherit it or share it, maybe?
epoller = await Epoller.make_root(base_task)
child_monitor = await ChildPidMonitor.make(base_task, epoller)
connection = make_connection(
base_task,
base_task.make_fd_handle(
near.FileDescriptor(describe_struct.connecting_fd)))
new_parent = Process(
task=base_task,
connection=connection,
loader=NativeLoader.make_from_symbols(base_task,
describe_struct.symbols),
epoller=epoller,
child_monitor=child_monitor,
environ=Environment.make_from_environ(base_task, environ),
stdin=base_task.make_fd_handle(near.FileDescriptor(0)),
stdout=base_task.make_fd_handle(near.FileDescriptor(1)),
stderr=base_task.make_fd_handle(near.FileDescriptor(2)),
)
return child_pid, new_parent
async def clone_child_task(
task: Task,
connection: Connection,
loader: NativeLoader,
monitor: ChildPidMonitor,
flags: CLONE,
trampoline_func: t.Callable[[FileDescriptor], Trampoline],
) -> t.Tuple[AsyncChildPid, Task]:
"""Clone a new child process and setup the sysif and task to manage it
We rely on trampoline_func to take a socket and give us a native function call with
arguments that will speak the rsyscall protocol over that socket.
We want to see EOF on our local socket if that remote socket is no longer being read;
for example, if the process exits or execs.
This is not automatic for us: Since the process might share its file descriptor table
with other processes, remote_sock might not be closed when the process exits or execs.
To ensure that we get an EOF, we use the ctid futex, which, thanks to
CLONE.CHILD_CLEARTID, will be cleared and receive a futex wakeup when the child
process exits or execs.
When we see that futex wakeup (from Python, with the futex integrated into our event
loop through launch_futex_monitor), we call shutdown(SHUT.RDWR) on the local socket
from the parent. This results in future reads returning EOF.
"""
# These flags are mandatory; if we don't use CLONE_VM then CHILD_CLEARTID doesn't work
# properly and our only other recourse to detect exec is to abuse robust futexes.
flags |= CLONE.VM | CLONE.CHILD_CLEARTID
# Open a channel which we'll use for the rsyscall connection
[(access_sock, remote_sock)] = await connection.open_async_channels(1)
# Create a trampoline that will start the new process running an rsyscall server
trampoline = trampoline_func(remote_sock)
# TODO it is unclear why we sometimes need to make a new mapping here, instead of
# allocating with our normal allocator; all our memory is already MAP.SHARED, I think.
# We should resolve this so we can use the normal allocator.
arena = Arena(await task.mmap(4096 * 2, PROT.READ | PROT.WRITE,
MAP.SHARED))
# Create the stack we'll need, and the zero-initialized futex
stack_value = loader.make_trampoline_stack(trampoline)
stack_buf = await task.malloc(Stack, 4096)
stack = await stack_buf.write_to_end(stack_value, alignment=16)
futex_pointer = await task.ptr(FutexNode(None, Int32(1)))
# it's important to start the processes in this order, so that the process
# process is the first process started; this is relevant in several
# situations, including unshare(NEWPID) and manipulation of ns_last_pid
child_pid = await monitor.clone(flags, stack, ctid=futex_pointer)
# We want to be able to rely on getting an EOF if the other side of the syscall
# connection is no longer being read (e.g., if the process exits or execs). Since the
# process might share its file descriptor table with other processes, remote_sock
# might not be closed when the process exits or execs. To ensure that we get an EOF,
# we use the ctid futex, which will be cleared on process exit or exec; we shutdown
# access_sock when the ctid futex is cleared, to get an EOF.
# We do this with launch_futex_monitor and a background coroutine.
futex_pid = await launch_futex_monitor(loader, monitor, futex_pointer)
async def shutdown_access_sock_on_futex_process_exit():
try:
await futex_pid.waitpid(W.EXITED)
except SyscallError:
# if the parent of the futex_process dies, this syscall
# connection is broken anyway, so shut it down.
pass
await access_sock.handle.shutdown(SHUT.RDWR)
# Running this in the background, without an associated object, is a bit dubious...
reset(shutdown_access_sock_on_futex_process_exit())
# Set up the new task with appropriately inherited namespaces, tables, etc.
# TODO correctly track all the namespaces we're in
if flags & CLONE.NEWPID:
pidns = far.PidNamespace(child_pid.pid.near.id)
else:
pidns = task.pidns
if flags & CLONE.FILES:
fd_table = task.fd_table
else:
fd_table = handle.FDTable(child_pid.pid.near.id, task.fd_table)
if flags & CLONE.NEWNS:
mountns = far.MountNamespace(child_pid.pid.near.id)
else:
mountns = task.mountns
child_task = Task(child_pid.pid, fd_table, task.address_space, pidns,
mountns)
child_task.sigmask = task.sigmask
# Move ownership of the remote sock into the task and store it so it isn't closed
remote_sock_handle = remote_sock.inherit(child_task)
await remote_sock.invalidate()
# Create the new syscall interface, which needs to use not just the connection,
# but also the futex process.
child_task.sysif = SyscallConnection(
logger.getChild(str(child_pid.pid.near)),
access_sock,
remote_sock_handle,
)
child_task.allocator = task.allocator.inherit(child_task)
return child_pid, child_task
