xml.c

/*
 * xml.c: XML based interfaces for the libvir library
 *
 * Copyright (C) 2005 Red Hat, Inc.
 *
 * See COPYING.LIB for the License of this software
 *
 * Daniel Veillard <veillard@redhat.com>
 */

#include "libvirt.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>
#include <xs.h>
#include <libxml/parser.h>
#include <libxml/tree.h>
#include <libxml/xpath.h>
#include "internal.h"
#include "hash.h"
#include "sexpr.h"
#include "xml.h"

/**
 * virBufferGrow:
 * @buf:  the buffer
 * @len:  the minimum free size to allocate
 *
 * Grow the available space of an XML buffer.
 *
 * Returns the new available space or -1 in case of error
 */
static int
virBufferGrow(virBufferPtr buf, unsigned int len) {
    int size;
    char *newbuf;

    if (buf == NULL) return(-1);
    if (len + buf->use < buf->size) return(0);

    size = buf->use + len + 1000;

    newbuf = (char *) realloc(buf->content, size);
    if (newbuf == NULL) {
        return(-1);
    }
    buf->content = newbuf;
    buf->size = size;
    return(buf->size - buf->use);
}

/**
 * virBufferAdd:
 * @buf:  the buffer to dump
 * @str:  the string
 * @len:  the number of bytes to add
 *
 * Add a string range to an XML buffer. if len == -1, the length of
 * str is recomputed to the full string.
 *
 * Returns 0 successful, -1 in case of internal or API error.
 */
int
virBufferAdd(virBufferPtr buf, const char *str, int len) {
    unsigned int needSize;

    if ((str == NULL) || (buf == NULL)) {
	return -1;
    }
    if (len == 0) return 0;

    if (len < 0)
        len = strlen(str);

    needSize = buf->use + len + 2;
    if (needSize > buf->size){
        if (!virBufferGrow(buf, needSize)){
            return(-1);
        }
    }

    memmove(&buf->content[buf->use], str, len);
    buf->use += len;
    buf->content[buf->use] = 0;
    return(0);
}

/**
 * virBufferVSprintf:
 * @buf:  the buffer to dump
 * @format:  the format
 * @argptr:  the variable list of arguments
 *
 * Do a formatted print to an XML buffer.
 *
 * Returns 0 successful, -1 in case of internal or API error.
 */
int
virBufferVSprintf(virBufferPtr buf, const char *format, ...) {
    int size, count;
    va_list locarg, argptr;

    if ((format == NULL) || (buf == NULL)) {
	return(-1);
    }
    size = buf->size - buf->use - 1;
    va_start(argptr, format);
    va_copy(locarg, argptr);
    while (((count = vsnprintf(&buf->content[buf->use], size, format,
                               locarg)) < 0) || (count >= size - 1)) {
	buf->content[buf->use] = 0;
	va_end(locarg);
	if (virBufferGrow(buf, 1000) < 0) {
	    return(-1);
	}
	size = buf->size - buf->use - 1;
	va_copy(locarg, argptr);
    }
    va_end(locarg);
    buf->use += count;
    buf->content[buf->use] = 0;
    return(0);
}

#if 0
/*
 * This block of function are now implemented by a xend poll in
 * xend_internal.c instead of querying the Xen store, code is kept
 * for reference of in case Xend may not be available in the future ...
 */
/**
 * virDomainGetXMLDevice:
 * @domain: a domain object
 * @sub: the xenstore subsection 'vbd', 'vif', ...
 * @dev: the xenstrore internal device number
 * @name: the value's name
 *
 * Extract one information the device used by the domain from xensttore
 *
 * Returns the new string or NULL in case of error
 */
static char *
virDomainGetXMLDeviceInfo(virDomainPtr domain, const char *sub, 
                          long dev, const char *name) {
    char s[256];
    unsigned int len = 0;

    snprintf(s, 255, "/local/domain/0/backend/%s/%d/%ld/%s",
             sub, domain->handle, dev, name);
    s[255] = 0;

    return xs_read(domain->conn->xshandle, 0, &s[0], &len);
}

/**
 * virDomainGetXMLDevice:
 * @domain: a domain object
 * @buf: the output buffer object
 * @dev: the xenstrore internal device number
 *
 * Extract and dump in the buffer informations on the device used by the domain
 *
 * Returns 0 in case of success, -1 in case of failure
 */
static int
virDomainGetXMLDevice(virDomainPtr domain, virBufferPtr buf, long dev) {
    char *type, *val;

    type = virDomainGetXMLDeviceInfo(domain, "vbd", dev, "type");
    if (type == NULL)
        return(-1);
    if (!strcmp(type, "file")) {
	virBufferVSprintf(buf, "    <disk type='file'>\n");
	val = virDomainGetXMLDeviceInfo(domain, "vbd", dev, "params");
	if (val != NULL) {
	    virBufferVSprintf(buf, "      <source file='%s'/>\n", val);
	    free(val);
	}
	val = virDomainGetXMLDeviceInfo(domain, "vbd", dev, "dev");
	if (val != NULL) {
	    virBufferVSprintf(buf, "      <target dev='%s'/>\n", val);
	    free(val);
	}
	val = virDomainGetXMLDeviceInfo(domain, "vbd", dev, "read-only");
	if (val != NULL) {
	    virBufferVSprintf(buf, "      <readonly/>\n", val);
	    free(val);
	}
	virBufferAdd(buf, "    </disk>\n", 12);
    } else if (!strcmp(type, "phy")) {
	virBufferVSprintf(buf, "    <disk type='device'>\n");
	val = virDomainGetXMLDeviceInfo(domain, "vbd", dev, "params");
	if (val != NULL) {
	    virBufferVSprintf(buf, "      <source device='%s'/>\n", val);
	    free(val);
	}
	val = virDomainGetXMLDeviceInfo(domain, "vbd", dev, "dev");
	if (val != NULL) {
	    virBufferVSprintf(buf, "      <target dev='%s'/>\n", val);
	    free(val);
	}
	val = virDomainGetXMLDeviceInfo(domain, "vbd", dev, "read-only");
	if (val != NULL) {
	    virBufferVSprintf(buf, "      <readonly/>\n", val);
	    free(val);
	}
	virBufferAdd(buf, "    </disk>\n", 12);
    } else {
        TODO
	fprintf(stderr, "Don't know how to handle device type %s\n", type);
    }
    free(type);

    return(0);
}

/**
 * virDomainGetXMLDevices:
 * @domain: a domain object
 * @buf: the output buffer object
 *
 * Extract the devices used by the domain and dumps then in the buffer
 *
 * Returns 0 in case of success, -1 in case of failure
 */
static int
virDomainGetXMLDevices(virDomainPtr domain, virBufferPtr buf) {
    int ret = -1;
    unsigned int num, i;
    long id;
    char **list = NULL, *endptr;
    char backend[200];
    virConnectPtr conn;

    if (!VIR_IS_CONNECTED_DOMAIN(domain))
	return(-1);
    
    conn = domain->conn;

    snprintf(backend, 199, "/local/domain/0/backend/vbd/%d", 
             virDomainGetID(domain));
    backend[199] = 0;
    list = xs_directory(conn->xshandle, 0, backend, &num);
    ret = 0;
    if (list == NULL)
        goto done;

    for (i = 0;i < num;i++) {
        id = strtol(list[i], &endptr, 10);
	if ((endptr == list[i]) || (*endptr != 0)) {
	    ret = -1;
	    goto done;
	}
	virDomainGetXMLDevice(domain, buf, id);
    }

done:
    if (list != NULL)
        free(list);

    return(ret);
}

/**
 * virDomainGetXMLInterface:
 * @domain: a domain object
 * @buf: the output buffer object
 * @dev: the xenstrore internal device number
 *
 * Extract and dump in the buffer informations on the interface used by
 * the domain
 *
 * Returns 0 in case of success, -1 in case of failure
 */
static int
virDomainGetXMLInterface(virDomainPtr domain, virBufferPtr buf, long dev) {
    char *type, *val;

    type = virDomainGetXMLDeviceInfo(domain, "vif", dev, "bridge");
    if (type == NULL) {
	virBufferVSprintf(buf, "    <interface type='default'>\n");
	val = virDomainGetXMLDeviceInfo(domain, "vif", dev, "mac");
	if (val != NULL) {
	    virBufferVSprintf(buf, "      <mac address='%s'/>\n", val);
	    free(val);
	}
	val = virDomainGetXMLDeviceInfo(domain, "vif", dev, "script");
	if (val != NULL) {
	    virBufferVSprintf(buf, "      <script path='%s'/>\n", val);
	    free(val);
	}
	virBufferAdd(buf, "    </interface>\n", 17);
    } else {
	virBufferVSprintf(buf, "    <interface type='bridge'>\n");
	virBufferVSprintf(buf, "      <source bridge='%s'/>\n", type);
	val = virDomainGetXMLDeviceInfo(domain, "vif", dev, "mac");
	if (val != NULL) {
	    virBufferVSprintf(buf, "      <mac address='%s'/>\n", val);
	    free(val);
	}
	val = virDomainGetXMLDeviceInfo(domain, "vif", dev, "script");
	if (val != NULL) {
	    virBufferVSprintf(buf, "      <script path='%s'/>\n", val);
	    free(val);
	}
	virBufferAdd(buf, "    </interface>\n", 17);
    }
    free(type);

    return(0);
}

/**
 * virDomainGetXMLInterfaces:
 * @domain: a domain object
 * @buf: the output buffer object
 *
 * Extract the interfaces used by the domain and dumps then in the buffer
 *
 * Returns 0 in case of success, -1 in case of failure
 */
static int
virDomainGetXMLInterfaces(virDomainPtr domain, virBufferPtr buf) {
    int ret = -1;
    unsigned int num, i;
    long id;
    char **list = NULL, *endptr;
    char backend[200];
    virConnectPtr conn;

    if (!VIR_IS_CONNECTED_DOMAIN(domain))
	return(-1);
    
    conn = domain->conn;

    snprintf(backend, 199, "/local/domain/0/backend/vif/%d", 
             virDomainGetID(domain));
    backend[199] = 0;
    list = xs_directory(conn->xshandle, 0, backend, &num);
    ret = 0;
    if (list == NULL)
        goto done;

    for (i = 0;i < num;i++) {
        id = strtol(list[i], &endptr, 10);
	if ((endptr == list[i]) || (*endptr != 0)) {
	    ret = -1;
	    goto done;
	}
	virDomainGetXMLInterface(domain, buf, id);
    }

done:
    if (list != NULL)
        free(list);

    return(ret);
}




/**
 * virDomainGetXMLBoot:
 * @domain: a domain object
 * @buf: the output buffer object
 *
 * Extract the boot informations used to start that domain
 *
 * Returns 0 in case of success, -1 in case of failure
 */
static int
virDomainGetXMLBoot(virDomainPtr domain, virBufferPtr buf) {
    char *vm, *str;

    if (!VIR_IS_DOMAIN(domain))
	return(-1);
    
    vm = virDomainGetVM(domain);
    if (vm == NULL)
        return(-1);

    virBufferAdd(buf, "  <os>\n", 7);
    str = virDomainGetVMInfo(domain, vm, "image/ostype");
    if (str != NULL) {
        virBufferVSprintf(buf, "    <type>%s</type>\n", str);
        free(str);
    }
    str = virDomainGetVMInfo(domain, vm, "image/kernel");
    if (str != NULL) {
        virBufferVSprintf(buf, "    <kernel>%s</kernel>\n", str);
        free(str);
    }
    str = virDomainGetVMInfo(domain, vm, "image/ramdisk");
    if (str != NULL) {
	if (str[0] != 0)
	    virBufferVSprintf(buf, "    <initrd>%s</initrd>\n", str);
        free(str);
    }
    str = virDomainGetVMInfo(domain, vm, "image/cmdline");
    if (str != NULL) {
	if (str[0] != 0)
	    virBufferVSprintf(buf, "    <cmdline>%s</cmdline>\n", str);
        free(str);
    }
    virBufferAdd(buf, "  </os>\n", 8);

    free(vm);
    return(0);
}

/**
 * virDomainGetXMLDesc:
 * @domain: a domain object
 * @flags: and OR'ed set of extraction flags, not used yet
 *
 * Provide an XML description of the domain. NOTE: this API is subject
 * to changes.
 *
 * Returns a 0 terminated UTF-8 encoded XML instance, or NULL in case of error.
 *         the caller must free() the returned value.
 */
char *
virDomainGetXMLDesc(virDomainPtr domain, int flags) {
    char *ret = NULL;
    virBuffer buf;
    virDomainInfo info;

    if (!VIR_IS_DOMAIN(domain))
	return(NULL);
    if (flags != 0)
	return(NULL);
    if (virDomainGetInfo(domain, &info) < 0)
        return(NULL);

    ret = malloc(1000);
    if (ret == NULL)
        return(NULL);
    buf.content = ret;
    buf.size = 1000;
    buf.use = 0;

    virBufferVSprintf(&buf, "<domain type='xen' id='%d'>\n",
                      virDomainGetID(domain));
    virBufferVSprintf(&buf, "  <name>%s</name>\n", virDomainGetName(domain));
    virDomainGetXMLBoot(domain, &buf);
    virBufferVSprintf(&buf, "  <memory>%lu</memory>\n", info.maxMem);
    virBufferVSprintf(&buf, "  <vcpu>%d</vcpu>\n", (int) info.nrVirtCpu);
    virBufferAdd(&buf, "  <devices>\n", 12);
    virDomainGetXMLDevices(domain, &buf);
    virDomainGetXMLInterfaces(domain, &buf);
    virBufferAdd(&buf, "  </devices>\n", 13);
    virBufferAdd(&buf, "</domain>\n", 10);
    
    buf.content[buf.use] = 0;
    return(ret);
}

#endif

/**
 * virDomainParseXMLOSDesc:
 * @xmldesc: string with the XML description
 * @buf: a buffer for the result S-Expr
 *
 * Parse the OS part of the XML description and add it to the S-Expr in buf
 * This is a temporary interface as the S-Expr interface
 * will be replaced by XML-RPC in the future. However the XML format should
 * stay valid over time.
 *
 * Returns 0 in case of success, -1 in case of error.
 */
static int
virDomainParseXMLOSDesc(xmlNodePtr node, virBufferPtr buf) {
    xmlNodePtr cur, txt;
    const xmlChar *type = NULL;
    const xmlChar *root = NULL;
    const xmlChar *kernel = NULL;
    const xmlChar *initrd = NULL;
    const xmlChar *cmdline = NULL;

    cur = node->children;
    while (cur != NULL) {
        if (cur->type == XML_ELEMENT_NODE) {
	    if ((type == NULL) && (xmlStrEqual(cur->name, BAD_CAST "type"))) {
	        txt = cur->children;
		if ((txt->type == XML_TEXT_NODE) && (txt->next == NULL))
		    type = txt->content;
	    } else if ((kernel == NULL) &&
	               (xmlStrEqual(cur->name, BAD_CAST "kernel"))) {
	        txt = cur->children;
		if ((txt->type == XML_TEXT_NODE) && (txt->next == NULL))
		    kernel = txt->content;
	    } else if ((root == NULL) &&
	               (xmlStrEqual(cur->name, BAD_CAST "root"))) {
	        txt = cur->children;
		if ((txt->type == XML_TEXT_NODE) && (txt->next == NULL))
		    root = txt->content;
	    } else if ((initrd == NULL) &&
	               (xmlStrEqual(cur->name, BAD_CAST "initrd"))) {
	        txt = cur->children;
		if ((txt->type == XML_TEXT_NODE) && (txt->next == NULL))
		    initrd = txt->content;
	    } else if ((cmdline == NULL) &&
	               (xmlStrEqual(cur->name, BAD_CAST "cmdline"))) {
	        txt = cur->children;
		if ((txt->type == XML_TEXT_NODE) && (txt->next == NULL))
		    cmdline = txt->content;
	    }
	}
        cur = cur->next;
    }
    if ((type != NULL) && (!xmlStrEqual(type, BAD_CAST "linux"))) {
        /* VIR_ERR_OS_TYPE */
	return(-1);
    }
    virBufferAdd(buf, "(linux ", 7);
    if (kernel == NULL) {
        /* VIR_ERR_NO_KERNEL */
	return(-1);
    }
    virBufferVSprintf(buf, "(kernel '%s')", (const char *) kernel);
    if (initrd != NULL)
	virBufferVSprintf(buf, "(ramdisk '%s')", (const char *) initrd);
    if (root == NULL) {
	const xmlChar *base, *tmp;
        /* need to extract root info from command line */
	if (cmdline == NULL) {
	    /* VIR_ERR_NO_ROOT */
	    return(-1);
	}
	base = cmdline;
	while (*base != 0) {
	    if ((base[0] == 'r') && (base[1] == 'o') && (base[2] == 'o') &&
	        (base[3] == 't')) {
		base += 4;
		break;
	    }
	    base++;
	}
	while ((*base == ' ') || (*base == '\t')) base++;
	if (*base == '=') {
	    base++;
	    while ((*base == ' ') || (*base == '\t')) base++;
	}
	tmp = base;
	while ((*tmp != 0) && (*tmp != ' ') && (*tmp != '\t')) tmp++;
	if (tmp == base) {
	    /* VIR_ERR_NO_ROOT */
	    return(-1);
	}
	root = xmlStrndup(base, tmp - base);
        virBufferVSprintf(buf, "(root '%s')", (const char *) root);
	xmlFree((xmlChar *) root);
	virBufferVSprintf(buf, "(args '%s')", (const char *) cmdline);
    } else {
        virBufferVSprintf(buf, "(root '%s')", (const char *) root);
	if (cmdline != NULL)
	    virBufferVSprintf(buf, "(args '%s')", (const char *) cmdline);
    }
    virBufferAdd(buf, ")", 1);
    return(0);
}

/**
 * virDomainParseXMLDiskDesc:
 * @xmldesc: string with the XML description
 * @buf: a buffer for the result S-Expr
 *
 * Parse the one disk in the XML description and add it to the S-Expr in buf
 * This is a temporary interface as the S-Expr interface
 * will be replaced by XML-RPC in the future. However the XML format should
 * stay valid over time.
 *
 * Returns 0 in case of success, -1 in case of error.
 */
static int
virDomainParseXMLDiskDesc(xmlNodePtr node, virBufferPtr buf) {
    xmlNodePtr cur;
    xmlChar *type = NULL;
    xmlChar *source = NULL;
    xmlChar *target = NULL;
    int ro = 0;
    int typ = 0;

    type = xmlGetProp(node, BAD_CAST "type");
    if (type != NULL) {
        if (xmlStrEqual(type, BAD_CAST "file")) typ = 0;
	else if (xmlStrEqual(type, BAD_CAST "block")) typ = 1;
	xmlFree(type);
    }
    cur = node->children;
    while (cur != NULL) {
        if (cur->type == XML_ELEMENT_NODE) {
	    if ((source == NULL) &&
	        (xmlStrEqual(cur->name, BAD_CAST "source"))) {

		if (typ == 0)
		    source = xmlGetProp(cur, BAD_CAST "file");
		else
		    source = xmlGetProp(cur, BAD_CAST "dev");
	    } else if ((target == NULL) &&
	               (xmlStrEqual(cur->name, BAD_CAST "target"))) {
	        target = xmlGetProp(cur, BAD_CAST "dev");
	    } else if (xmlStrEqual(cur->name, BAD_CAST "readonly")) {
	        ro = 1;
	    }
	}
        cur = cur->next;
    }

    if (source == NULL) {
        /* VIR_ERR_NO_SOURCE */
	if (target != NULL)
	    xmlFree(target);
	return(-1);
    }
    if (target == NULL) {
        /* VIR_ERR_NO_TARGET */
	if (source != NULL)
	    xmlFree(source);
	return(-1);
    }
    virBufferAdd(buf, "(vbd ", 5);
    if (target[0] == '/')
	virBufferVSprintf(buf, "(dev '%s')", (const char *) target);
    else
	virBufferVSprintf(buf, "(dev '/dev/%s')", (const char *) target);
    if (typ == 0)
        virBufferVSprintf(buf, "(uname 'file:%s')", source);
    else if (typ == 1) {
        if (source[0] == '/')
	    virBufferVSprintf(buf, "(uname 'phys:%s')", source);
	else
	    virBufferVSprintf(buf, "(uname 'phys:/dev/%s')", source);
    }
    if (ro == 0)
        virBufferVSprintf(buf, "(mode 'w')");
    else if (ro == 1)
        virBufferVSprintf(buf, "(mode 'r')");

    virBufferAdd(buf, ")", 1);
    xmlFree(target);
    xmlFree(source);
    return(0);
}

/**
 * virDomainParseXMLIfDesc:
 * @xmldesc: string with the XML description
 * @buf: a buffer for the result S-Expr
 *
 * Parse the one interface the XML description and add it to the S-Expr in buf
 * This is a temporary interface as the S-Expr interface
 * will be replaced by XML-RPC in the future. However the XML format should
 * stay valid over time.
 *
 * Returns 0 in case of success, -1 in case of error.
 */
static int
virDomainParseXMLIfDesc(xmlNodePtr node, virBufferPtr buf) {
    xmlNodePtr cur;
    xmlChar *type = NULL;
    xmlChar *source = NULL;
    xmlChar *mac = NULL;
    xmlChar *script = NULL;
    int typ = 0;

    type = xmlGetProp(node, BAD_CAST "type");
    if (type != NULL) {
        if (xmlStrEqual(type, BAD_CAST "bridge")) typ = 0;
	else if (xmlStrEqual(type, BAD_CAST "ethernet")) typ = 1;
	xmlFree(type);
    }
    cur = node->children;
    while (cur != NULL) {
        if (cur->type == XML_ELEMENT_NODE) {
	    if ((source == NULL) &&
	        (xmlStrEqual(cur->name, BAD_CAST "source"))) {

		if (typ == 0)
		    source = xmlGetProp(cur, BAD_CAST "bridge");
		else
		    source = xmlGetProp(cur, BAD_CAST "dev");
	    } else if ((mac == NULL) &&
	               (xmlStrEqual(cur->name, BAD_CAST "mac"))) {
	        mac = xmlGetProp(cur, BAD_CAST "address");
	    } else if ((script == NULL) &&
	               (xmlStrEqual(cur->name, BAD_CAST "script"))) {
	        script = xmlGetProp(cur, BAD_CAST "path");
	    }
	}
        cur = cur->next;
    }

    virBufferAdd(buf, "(vif ", 5);
    if (mac != NULL)
	virBufferVSprintf(buf, "(mac '%s')", (const char *) mac);
    if (source != NULL) {
	if (typ == 0)
	    virBufferVSprintf(buf, "(bridge '%s')", (const char *) source);
	else /* TODO does that work like that ? */
	    virBufferVSprintf(buf, "(dev '%s')", (const char *) source);
    }
    if (script != NULL)
        virBufferVSprintf(buf, "(script '%s')", script);

    virBufferAdd(buf, ")", 1);
    if (mac != NULL)
	xmlFree(mac);
    if (source != NULL)
	xmlFree(source);
    if (script != NULL)
	xmlFree(script);
    return(0);
}

/**
 * virDomainParseXMLDesc:
 * @xmldesc: string with the XML description
 *
 * Parse the XML description and turn it into the xend sexp needed to
 * create the comain. This is a temporary interface as the S-Expr interface
 * will be replaced by XML-RPC in the future. However the XML format should
 * stay valid over time.
 *
 * Returns the 0 terminatedi S-Expr string or NULL in case of error.
 *         the caller must free() the returned value.
 */
char *
virDomainParseXMLDesc(const char *xmldesc, char **name) {
    xmlDocPtr xml = NULL;
    xmlNodePtr node;
    char *ret = NULL;
    virBuffer buf;
    xmlChar *prop;
    xmlXPathObjectPtr obj = NULL;
    xmlXPathContextPtr ctxt = NULL;
    int i, res;

    if (name != NULL)
	*name = NULL;
    ret = malloc(1000);
    if (ret == NULL)
        return(NULL);
    buf.content = ret;
    buf.size = 1000;
    buf.use = 0;

    xml = xmlReadDoc((const xmlChar *) xmldesc, "domain.xml", NULL,
		 XML_PARSE_NOENT | XML_PARSE_NONET | 
		 XML_PARSE_NOERROR | XML_PARSE_NOWARNING);
    if (xml == NULL) {
        goto error;
    }
    node = xmlDocGetRootElement(xml);
    if ((node == NULL) || (!xmlStrEqual(node->name, BAD_CAST "domain")))
        goto error;

    prop = xmlGetProp(node, BAD_CAST "type");
    if (prop != NULL) {
        if (!xmlStrEqual(prop, BAD_CAST "xen")) {
	    xmlFree(prop);
	    goto error;
	}
	xmlFree(prop);
    }
    virBufferAdd(&buf, "(vm ", 4);
    ctxt = xmlXPathNewContext(xml);
    if (ctxt == NULL) {
        goto error;
    }
    /*
     * extract soem of the basics, name, memory, cpus ...
     */
    obj = xmlXPathEval(BAD_CAST "string(/domain/name[1])", ctxt);
    if ((obj == NULL) || (obj->type != XPATH_STRING) || 
        (obj->stringval == NULL) || (obj->stringval[0] == 0)) {
	/* VIR_ERR_NO_NAME */
        goto error;
    }
    virBufferVSprintf(&buf, "(name '%s')", obj->stringval);
    if (name != NULL)
	*name = strdup((const char *) obj->stringval);
    xmlXPathFreeObject(obj);

    obj = xmlXPathEval(BAD_CAST "number(/domain/memory[1])", ctxt);
    if ((obj == NULL) || (obj->type != XPATH_NUMBER) ||
        (obj->floatval < 64000)) {
	virBufferVSprintf(&buf, "(memory 128)(maxmem 128)");
    } else {
        unsigned long mem = (obj->floatval / 1024);
        virBufferVSprintf(&buf, "(memory %lu)(maxmem %lu)", mem, mem);
    }
    xmlXPathFreeObject(obj);

    obj = xmlXPathEval(BAD_CAST "number(/domain/vcpu[1])", ctxt);
    if ((obj == NULL) || (obj->type != XPATH_NUMBER) ||
        (obj->floatval <= 0)) {
	virBufferVSprintf(&buf, "(vcpus 1)");
    } else {
        unsigned int cpu = (unsigned int) obj->floatval;
        virBufferVSprintf(&buf, "(vcpus %u)", cpu);
    }
    xmlXPathFreeObject(obj);

    /* analyze of the os description */
    virBufferAdd(&buf, "(image ", 7);
    obj = xmlXPathEval(BAD_CAST "/domain/os[1]", ctxt);
    if ((obj == NULL) || (obj->type != XPATH_NODESET) ||
        (obj->nodesetval == NULL) ||
	(obj->nodesetval->nodeNr != 1)) {
	/* VIR_ERR_NO_OS */
        goto error;
    }
    res = virDomainParseXMLOSDesc(obj->nodesetval->nodeTab[0], &buf);
    if (res != 0) {
        goto error;
    }
    xmlXPathFreeObject(obj);
    virBufferAdd(&buf, ")", 1);

    /* analyze of the devices */
    obj = xmlXPathEval(BAD_CAST "/domain/devices/disk", ctxt);
    if ((obj == NULL) || (obj->type != XPATH_NODESET) ||
        (obj->nodesetval == NULL) ||
	(obj->nodesetval->nodeNr < 1)) {
	/* VIR_ERR_NO_DEVICE */
        goto error;
    }
    for (i = 0;i < obj->nodesetval->nodeNr;i++) {
	virBufferAdd(&buf, "(device ", 8);
	res = virDomainParseXMLDiskDesc(obj->nodesetval->nodeTab[i], &buf);
	if (res != 0) {
	    goto error;
	}
	virBufferAdd(&buf, ")", 1);
    }
    xmlXPathFreeObject(obj);
    obj = xmlXPathEval(BAD_CAST "/domain/devices/interface", ctxt);
    if ((obj != NULL) && (obj->type == XPATH_NODESET) &&
        (obj->nodesetval != NULL) && (obj->nodesetval->nodeNr >= 0)) {
	for (i = 0;i < obj->nodesetval->nodeNr;i++) {
	    virBufferAdd(&buf, "(device ", 8);
	    res = virDomainParseXMLIfDesc(obj->nodesetval->nodeTab[i], &buf);
	    if (res != 0) {
		goto error;
	    }
	    virBufferAdd(&buf, ")", 1);
	}
    }
    xmlXPathFreeObject(obj);


    virBufferAdd(&buf, ")", 1); /* closes (vm */
    buf.content[buf.use] = 0;

    xmlXPathFreeContext(ctxt);
    xmlFreeDoc(xml);
    
    return(ret);

error:
    if (name != NULL) {
        if (*name != NULL)
	    free(*name);
	*name = NULL;
    }
    if (obj != NULL)
        xmlXPathFreeObject(obj);
    if (ctxt != NULL)
        xmlXPathFreeContext(ctxt);
    if (xml != NULL)
        xmlFreeDoc(xml);
    if (ret != NULL)
        free(ret);
    return(NULL);
}