The Design and Implementation of the Anykernel and Rump Kernels

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off_t
rump___sysimpl_lseek(int fd, off_t offset, int whence)
{
register_t retval[2] = {0, 0};
int error = 0;
off_t rv = -1;
struct sys_lseek_args callarg;
SPARG(&callarg, fd) = fd;
SPARG(&callarg, PAD) = 0;
SPARG(&callarg, offset) = offset;
SPARG(&callarg, whence) = whence;
}
error = rsys_syscall(SYS_lseek, &callarg, sizeof(callarg), retval);
rsys_seterrno(error);
if (error == 0) {
if (sizeof(off_t) > sizeof(register_t))
rv = *(off_t *)retval;
else
rv = *retval;
}
return rv;
Figure 3.12: Call stub for rump_sys_lseek(). The arguments from the client
are marshalled into the argument structure which is supplied to the kernel entry
point. The execution of the system call is requested using the rsys_syscall()
routine. This routine invokes either a direct function call into the rump kernel or a
remote request, depending on if the rump kernel is local or remote, respectively.
generated into sys/rump/librump/rumpkern/rump_syscalls.c — in our example
this arranging means moving the arguments that rump_sys_lseek() was called
with into the fields of struct sys_lseek_args. The wrapper for lseek is presented
in Figure 3.12. The name of the wrapper in the illustration does not match
rump_sys_lseek(). but the reference will be correctly translated by an alias in the
rump system call header. We will not go into details, except to say that the reason
for it is to support compatibility system calls. For interested parties, the details are
available in the rump_syscalls.h header file.