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GNU LESSER GENERAL PUBLIC LICENSE
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Wed Nov 2 13:44:47 CET 2005 Daniel Veillard <veillard@redhat.com>
* src/libxen.c src/Makefile.am include/libxen.h configure.in
Makefile.am COPYING.LIB: creation

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## Process this file with automake to produce Makefile.in
SUBDIRS = src #docs
EXTRA_DIST = libxen.spec.in libxen.spec COPYING.LIB \
libxen.pc.in libxen.pc
pkgconfigdir = $(libdir)/pkgconfig
pkgconfig_DATA = libxen.pc

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dnl Process this file with autoconf to produce a configure script.
AC_INIT(entities.c)
AM_CONFIG_HEADER(config.h)
AC_CANONICAL_HOST
LIBXEN_MAJOR_VERSION=0
LIBXEN_MINOR_VERSION=0
LIBXEN_MICRO_VERSION=1
LIBXEN_MICRO_VERSION_SUFFIX=
LIBXEN_VERSION=$LIBXEN_MAJOR_VERSION.$LIBXEN_MINOR_VERSION.$LIBXEN_MICRO_VERSION$LIBXEN_MICRO_VERSION_SUFFIX
LIBXEN_VERSION_INFO=`expr $LIBXEN_MAJOR_VERSION + $LIBXEN_MINOR_VERSION`:$LIBXEN_MICRO_VERSION:$LIBXEN_MINOR_VERSION
LIBXEN_VERSION_NUMBER=`expr $LIBXEN_MAJOR_VERSION \* 10000 + $LIBXEN_MINOR_VERSION \* 100 + $LIBXEN_MICRO_VERSION`
if test -f CVS/Entries; then
extra=`grep ChangeLog CVS/Entries | grep -v LIBXEN | sed -e s\%/ChangeLog/1\.%% -e s\%/.*$%%`
echo extra=$extra
if test "$extra" != ""
then
LIBXEN_VERSION_EXTRA="-CVS$extra"
fi
fi
AC_SUBST(LIBXEN_MAJOR_VERSION)
AC_SUBST(LIBXEN_MINOR_VERSION)
AC_SUBST(LIBXEN_MICRO_VERSION)
AC_SUBST(LIBXEN_VERSION)
AC_SUBST(LIBXEN_VERSION_INFO)
AC_SUBST(LIBXEN_VERSION_NUMBER)
AC_SUBST(LIBXEN_VERSION_EXTRA)
VERSION=${LIBXEN_VERSION}
AM_INIT_AUTOMAKE(libxen, $VERSION)

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1/ go for a minimal library first, expand on use cases
2/ reuse xenctrl.h / libxenctrl in a first implementation, but make
sure to clearly isolate the bits calling them
3/

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arch/xen/kernel/evtchn.c: Communication via Xen event channels
->HYPERVISOR_xen_version call
->HYPERVISOR_physdev_op call
->HYPERVISOR_event_channel_op call
-> global HYPERVISOR_shared_info
arch/xen/kernel/fixup.c: binary rewrinting for threads TLS
-> message to suppress... + boot delay
arch/xen/kernel/gnttab.c: memory access and sharing
inline assemby from privcmd.c using TRAP_INSTR macro to do an hypervisor
call apparently.
arch/xen/kernel/reboot.c:
-> HYPERVISOR_suspend call
include/asm-xen/asm-i386/hypercall.h:
-> assembly macro for the hypervisor calls
tools/libxc/xc_*.c: library for xen control
tools/libxc/xc_private.h:
-> Xen hypervisor call is an ioctl() with an privcmd_hypercall_t parameter
xc_domain.c:
-> API for all domain supervisor calls, create, memory, cpu weight, destroy
=> Fraser all over the place ...
/Xen/xen-unstable.hg/tools/libxc
The hypervisor calls are defined as inlined functions in xc_private.h
This is GPL and not installed.

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About a libxen library
======================
Functional description:
-----------------------
Small C library to be able to control Xen Linux guest, i.e.
provide the following operations for Xen guest domains running Linux
from domain 0 code linked to the library (running as root):
- start
- stop
- suspend
- resume
- monitor
More advanced features should be allowed as future extensions, but
are not expected to be provided in first shipment.
Open enough Licence that customers can link their apps to it (LGPL)
Small and contained enough that we can use it as a way to
provide API and ABI stability in spite if the evolution of Xen
existing API and hypervisor calls.
The current state of Xen userland:
----------------------------------
the existing Xen 3.0 userland code is mostly based on tiny C functions
using direct hypervisor calls (or /proc/xen/ interfaces) and a lot of
Python code on top driving the hypervisor.
The C code is relatively hairy, functions with 10 parameters or more
are not uncommon, and it is very low level usually without comment about
the function or its arguments. They are usually only called once in the
whole tree by the python bindings. In essence it looks like the Xen project
was not implemented with the idea of reusing that part of the code by
applications.
Indeed most of the userland code coming with Xen is built on Python,
like xend the xen daemon running on domain 0 or the xenstored daemon which
manage the state of the domains launched.
Rebuilding a library ?:
-----------------------
Providing a library at the C level to drive domain execution is in a
very large part a rimplementation of existing code but in a different way
and somehow with different goals for the code. The existing Licence (GPL)
makes it uneasy, we can't copy GPL code to put it in a LGPL'ed library,
and rewriting everything while looking at the Xen code will inevitably
lead to code similarities especially with this kind of system code. Plus
we will still need to run xend and probably xenstored to not diverge
completely from Xen existing code base.
The IBM way:
------------
Here is supposition about code that I can't instanciate except by looking
at said code but it looks that IBM also needed a C programmatic API to
manage the Xen domain definitions. Their solution was to build (Rusty
Russell did this) an LGPL C API connecting directly to the xenstore
daemon (./tools/xenstore/*). In a way this is quite more fragile as it depends
on the whole existing stack of the Xen code, but it isolate the API
from the implementation details of the current Xen source (API in
./tools/xenstore/xs.h). The goal seems to be more about testing and controlling
the xen store daemon, but it shows a different approach to decouple client
API/ABI from the Xen existing code.
Open question:
---------------
To what extent should libxen be a rewrite or an isolation layer around
some of the existing code ?
Rewrite:
Pros:
- avoid the GPL Licence problem potentially more users
- allow do build a cleaner more stable layer
- the existing code is frigthening
Cons:
- awful lot of work debugging very hard
- will still require existing Xen code to be running
- splitting interfaces is hard politically and lower the
Open Source efforts toward the project
Wrappers on top of existing code:
Pros:
- much smaller code rewrite
- benefits from the bugfixes injected by other patchers upstream
Cons:
- Licence constraint GPL only for apps
- API/ABI isolation may not be easier in that way
Potentially the API could be implemented as a layer on top of the existing
libxc C code library and then progressively migrating out the existing
dependance to Xen code as the interfaces stabilize.
Daniel Veillard <veillard@redhat.com>
Mon Oct 24 18:40:19 CEST 2005

80
include/libxen.h Normal file
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/*
* libxen.h: interface for the libxen library to handle Xen domains
* from a process running in domain 0
*
* Copyright (C) 2005 Red Hat, Inc.
*
* See COPYING.LIB for the License of this software
*
* Daniel Veillard <veillard@redhat.com>
*/
#ifndef __XEN_XENLIB_H__
#define __XEN_XENLIB_H__
#ifdef __cplusplus
extern "C" {
#endif
/**
* xenConnect:
*
* a xenConnect is a private structure representing a connection to
* the Xen Hypervisor.
*/
typedef struct _xenConnect xenConnect;
/**
* xenConnectPtr:
*
* a xenConnectPtr is pointer to a xenConnect private structure, this is the
* type used to reference a connection to the Xen Hypervisor in the API.
*/
typedef xenConnect *xenConnectPtr;
/**
* xenDomain:
*
* a xenDomain is a private structure representing a Xen domain.
*/
typedef struct _xenDomain xenDomain;
/**
* xenDomainPtr:
*
* a xenDomainPtr is pointer to a xenDomain private structure, this is the
* type used to reference a Xen domain in the API.
*/
typedef xenDomain *xenDomainPtr;
/**
* xenDomainFlags:
*
* Flags OR'ed together to provide specific behaviour when creating a
* Domain.
*/
typedef enum {
XEN_DOMAIN_NONE = 0
} xenDomainFlags;
/*
* Connection and disconnections to the Hypervisor
*/
xenConnectPtr xenOpenConnect (const char *name);
int xenCloseConnect (xenConnectPtr conn);
unsigned long xenGetVersion (xenConnectPtr conn);
/*
* Domain creation and destruction
*/
xenDomainPtr xenCreateLinuxDomain (xenConnectPtr conn,
const char *kernel_path,
const char *initrd_path,
const char *cmdline,
unsigned int flags);
#ifdef __cplusplus
}
#endif
#endif /* __XEN_XENLIB_H__ */

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src/Makefile.am Normal file
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## Process this file with automake to produce Makefile.in
INCLUDES = -I$(top_builddir)/include -I@srcdir@/include
lib_LTLIBRARIES = libxen.la
libxen_la_LIBADD =
libxen_la_LDFLAGS = -version-info @LIBXML_VERSION_INFO@
libxen_la_SOURCES = libxen.c

76
src/libxen.c Normal file
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/*
* libxen.h: Main interfaces for the libxen library to handle virtualization
* domains from a process running in domain 0
*
* Copyright (C) 2005 Red Hat, Inc.
*
* See COPYING.LIB for the License of this software
*
* Daniel Veillard <veillard@redhat.com>
*/
#include "libxen.h"
#include "memory.h"
#include "internal.h"
/*
* TODO:
* - use lock to protect against concurrent accesses ?
* - use reference counting to garantee coherent pointer state ?
*/
#define XEN_CONNECT_MAGIC 0x4F23DEAD
/**
* _xenConnect:
*
* Internal structure associated to a connection
*/
struct _xenConnect {
unsigned int magic; /* specific value to check */
int handle; /* internal handle used for hypercall */
}
/**
* xenGetConnect:
* @name: optional argument currently unused, pass NULL
*
* This function should be called first to get a connection to the
* Hypervisor
*
* Returns a pointer to the hypervisor connection or NULL in case of error
*/
xenConnectPtr
xenOpenConnect(const char *name ATTRIBUTE_UNUSED) {
return(NULL);
}
/**
* xenCloseConnect:
* @conn: pointer to the hypervisor connection
*
* This function closes the connection to the Hypervisor. This should
* not be called if further interaction with the Hypervisor are needed
* especially if there is running domain which need further monitoring by
* the application.
*
* Returns 0 in case of success or -1 in case of error.
*/
int
xenCloseConnect(xenConnectPtr conn) {
if ((conn == NULL) || (conn->magic != XEN_CONNECT_MAGIC))
return(-1);
/*
* TODO:
* Free the domain pointers associated to this connection
*/
conn->magic = -1;
free(conn);
return(0);
}
/**
* xenGetVersion:
* @conn: pointer to the hypervisor connection
*
* Get the version level of the Hypervisor running