The Design and Implementation of the Anykernel and Rump Kernels

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pid_t
rumpclient_fork()
{
pid_t rv;
cookie = rumpclient_prefork();
switch ((rv = host_fork())) {
case 0:
rumpclient_fork_init(cookie);
break;
default:
break;
case -1:
error();
}
}
return rv;
Figure 3.36: Implementation of fork() on the client side. The prefork
cookie is used to connect the newly created child to the parent when the new remote
process performs the rump kernel handshake.
Since calling exec replaces the memory image of a process with that of a new one
from disk, we lose all of the rump client state in memory. Important state in memory
includes for example rumpclient’s file descriptors. For hijacked clients the clearing
of memory additionally means we will lose e.g. the dup2 file descriptor alias table.
Recall, though, that exec closes only those file descriptors which are set FD_CLOEXEC.
Before calling the host’s execve, we first augment the environment to contain all
the rump client state; librumpclient and librumphijack have their own sets of state
as was pointed out above. After that, execve() is called with the augmented
environment. When the rump client constructor runs, it will search the environment
for these variables. If found, it will initialize state from them instead of starting from
a pristine state.