Re: [PATCH 2/2] ptrace_vm: ptrace for syscall emulation virtual machines

[Renzo Davoli <renzo@cs.unibo.it>]

Dear Cong,

Thank you for the detailed analysis of the code.
I'll change the code taking care of your observations asap.

On Mon, Mar 16, 2009 at 04:15:08PM +0800, Am??rico Wang wrote:
> >I have updated the patch, now it should be (more) consistent
> >with the Coding Style specifications.
> You can use scripts/checkpatch.pl to check it before sending.
I read the coding style document and I used the perl script.
However, the script is not able to cope with all the style specifications
and I may have missed something more. 
> 
> >UML tests at startup which features are provided and uses PTRACE_VM or
> >PTRACE_SYSEMU (or nothing). PTRACE_VM and/or PTRACE_SYSEMU support can be
> >disabled by command line flags.
> So what? PTRACE_VM is only supported in UML with this patch,
> UML still has to use PTRACE_SYSEMU on x86_32.
> 
> Am I missing something? :)
This patch [2/2] is for UML (host and guest). Patch #1 provides PTRACE_VM
for all the architectures supporting ptrace via tracehook.
By applying both patches PTRACE_VM is available in the following architectures:
x86*, sparc*, s390, powerpc*, ia64, sh* and um.
(I have not tested all these architectures, but the patch applies to the core ptrace
code, shared by all of them).
Ptrace_vm then provides the same speedup of PTRACE_SYSEMU extending its support:
- to other architectures: ports of UML or similar code for other architectures can
use it
- to other applications: PTRACE_SYSEMU supports the virtualization of all the system calls
while by PTRACE_VM the VM monitor can virtualize some of the system calls, depending on
some condition e.g. the value of a parameter. It is possible in this way give a faster
implementation to partial virtual machines like my umview.  

With patch #2 user-mode linux also uses ptrace_vm where available.

renzo