[Vm-dev] Re: Cog Rump Xen unikernel (spur mmap)

[Ben Coman]

On Thu, Dec 17, 2015 at 1:43 AM, Ben Coman <btc at openinworld.com> wrote:
> I'm having a go at getting this working with the Spur svn sources per...
> http://www.mirandabanda.org/cogblog/compiling-the-vm/

@Eliot,
I am currently stuck on Spur's requirement for mmap.
Could you describe this requirement and any ideas on path to proceed
to check compatibilty with these...

https://github.com/rumpkernel/wiki/wiki/Info:-FAQ
says "For simplicity reasons, the Rumprun unikernel does not support
virtual memory -- unnecessary in a unikernel -- nor does it support
signals the traditional way. That means that programs which absolutely
depend on things like fork(),execve(), mmap() and sigaction() may not
work correctly. In some cases we provide a small amount of cheap
emulation for common cases (e.g. mmap(MAP_ANON))"

http://rumpkernel.org/misc/usenix-login-2014/login_1410_03_kantee.pdf
says "The more or less only negative effect caused by the lack of
virtual memory support is that the mmap() system call cannot be fully
handled by a rump kernel. A number of workarounds are possible for
applications that absolutely need to use mmap(). For example, the
bozohttpd Web server uses mmap() to read the files it serves, so when
running bozohttpd on top of a rump kernel, we simply read the mmap’d
window into memory at the time the mapping is made instead of
gradually faulting pages in. A perfect emulation of mmap() is hard to
achieve, but one that works for most practical purposes is easy to
achieve"

cheers -ben

P.S. Here is the compilation error...

platforms/unix/vm/sqUnixSpurMemory.c:72:3: error: #error "Spur requires mmap"
 # error "Spur requires mmap"
   ^
platforms/unix/vm/sqUnixSpurMemory.c: In function ‘sqAllocateMemory’:
platforms/unix/vm/sqUnixSpurMemory.c:108:47: warning: passing argument
3 of ‘sqAllocateMemorySegmentOfSizeAboveAllocatedSizeInto’ from
incompatible pointer type
     (roundUpToPage(desiredHeapSize), address, &allocBytes);
                                               ^
In file included from platforms/unix/vm/sqUnixSpurMemory.c:33:0:
platforms/Cross/vm/sq.h:88:14: note: expected ‘sqInt *’ but argument
is of type ‘long unsigned int *’
 extern void *sqAllocateMemorySegmentOfSizeAboveAllocatedSizeInto(sqInt
sz, void *minAddr, sqInt *asp);
              ^
Makefile:276: recipe for target 'sqUnixSpurMemory.o' failed
make[1]: *** [sqUnixSpurMemory.o] Error 1
Makefile:407: recipe for target 'vm/vm.a' failed
make: *** [vm/vm.a] Error 2