conf.c

/**
 * conf.c: parser for a subset of the Python encoded Xen configuration files
 *
 * Copyright (C) 2006, 2007, 2008, 2009 Red Hat, Inc.
 *
 * See COPYING.LIB for the License of this software
 *
 * Daniel Veillard <veillard@redhat.com>
 */

#include <config.h>

#include <string.h>

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#include "virterror_internal.h"
#include "buf.h"
#include "conf.h"
#include "util.h"
#include "c-ctype.h"
#include "memory.h"

/************************************************************************
 *									*
 *	Structures and macros used by the mini parser			*
 *									*
 ************************************************************************/

typedef struct _virConfParserCtxt virConfParserCtxt;
typedef virConfParserCtxt *virConfParserCtxtPtr;

struct _virConfParserCtxt {
    const char* filename;
    const char* base;
    const char* cur;
    const char *end;
    int line;

    virConfPtr conf;
};

#define CUR (*ctxt->cur)
#define NEXT if (ctxt->cur < ctxt->end) ctxt->cur++;
#define IS_EOL(c) (((c) == '\n') || ((c) == '\r'))

#define SKIP_BLANKS_AND_EOL                                             \
  do { while ((ctxt->cur < ctxt->end) && (c_isblank(CUR) || IS_EOL(CUR))) { \
         if (CUR == '\n') ctxt->line++;	                                \
         ctxt->cur++;}} while (0)
#define SKIP_BLANKS                                                     \
  do { while ((ctxt->cur < ctxt->end) && (c_isblank(CUR)))              \
          ctxt->cur++; } while (0)

/************************************************************************
 *									*
 *		Structures used by configuration data			*
 *									*
 ************************************************************************/

typedef struct _virConfEntry virConfEntry;
typedef virConfEntry *virConfEntryPtr;

struct _virConfEntry {
    virConfEntryPtr next;
    char* name;
    char* comment;
    virConfValuePtr value;
};

struct _virConf {
    const char* filename;
    virConfEntryPtr entries;
};

/**
 * virConfError:
 * @ctxt: the parser context if available or NULL
 * @error: the error number
 * @info: extra information string
 *
 * Handle an error at the xend daemon interface
 */
static void
virConfError(virConfParserCtxtPtr ctxt,
             virErrorNumber error, const char *info)
{
    const char *format;

    if (error == VIR_ERR_OK)
        return;

    /* Construct the string 'filename:line: info' if we have that. */
    if (ctxt && ctxt->filename) {
        virRaiseError(NULL, NULL, NULL, VIR_FROM_CONF, error, VIR_ERR_ERROR,
                        info, ctxt->filename, NULL,
                        ctxt->line, 0,
                        "%s:%d: %s", ctxt->filename, ctxt->line, info);
    } else {
        format = virErrorMsg(error, info);
        virRaiseError(NULL, NULL, NULL, VIR_FROM_CONF, error, VIR_ERR_ERROR,
                        info, NULL, NULL,
                        ctxt ? ctxt->line : 0, 0,
                        format, info);
    }
}


/************************************************************************
 *									*
 *		Structures allocations and deallocations		*
 *									*
 ************************************************************************/

/**
 * virConfFreeList:
 * @list: the list to free
 *
 * Free a list
 */
static void
virConfFreeList(virConfValuePtr list)
{
    virConfValuePtr next;

    while (list != NULL) {
        next = list->next;
        list->next = NULL;
        virConfFreeValue(list);
        list = next;
    }
}

/**
 * virConfFreeValue:
 * @val: the value to free
 *
 * Free a value
 */
void
virConfFreeValue(virConfValuePtr val)
{
    if (val == NULL)
        return;
    if (val->type == VIR_CONF_STRING &&
        val->str != NULL)
        VIR_FREE(val->str);
    if (val->type == VIR_CONF_LIST &&
        val->list != NULL)
        virConfFreeList(val->list);
    VIR_FREE(val);
}

virConfPtr
virConfNew(void)
{
    virConfPtr ret;

    if (VIR_ALLOC(ret) < 0) {
        virConfError(NULL, VIR_ERR_NO_MEMORY, _("allocating configuration"));
        return(NULL);
    }
    ret->filename = NULL;

    return(ret);
}

/**
 * virConfCreate:
 * @filename: the name to report errors
 *
 * Create a configuration internal structure
 *
 * Returns a pointer or NULL in case of error.
 */
static virConfPtr
virConfCreate(const char *filename)
{
    virConfPtr ret = virConfNew();
    if (ret)
        ret->filename = filename;
    return(ret);
}

/**
 * virConfAddEntry:
 * @conf: the conf structure
 * @name: name of the entry or NULL for comment
 * @value: the value if any
 * @comm: extra comment for that entry if any
 *
 * add one entry to the conf, the parameters are included in the conf
 * if successful and freed on virConfFree()
 *
 * Returns a pointer to the entry or NULL in case of failure
 */
static virConfEntryPtr
virConfAddEntry(virConfPtr conf, char *name, virConfValuePtr value, char *comm)
{
    virConfEntryPtr ret, prev;

    if (conf == NULL)
        return(NULL);
    if ((comm == NULL) && (name == NULL))
        return(NULL);

    if (VIR_ALLOC(ret) < 0) {
        virConfError(NULL, VIR_ERR_NO_MEMORY, _("allocating configuration"));
        return(NULL);
    }

    ret->name = name;
    ret->value = value;
    ret->comment = comm;

    if (conf->entries == NULL) {
        conf->entries = ret;
    } else {
        prev = conf->entries;
        while (prev->next != NULL)
            prev = prev->next;
        prev->next = ret;
    }
    return(ret);
}

/************************************************************************
 *									*
 *			Serialization					*
 *									*
 ************************************************************************/

/**
 * virConfSaveValue:
 * @buf: output buffer
 * @val: a value
 *
 * Serialize the value to the buffer
 *
 * Returns 0 in case of success, -1 in case of error.
 */
static int
virConfSaveValue(virBufferPtr buf, virConfValuePtr val)
{
    if (val == NULL)
        return(-1);
    switch (val->type) {
        case VIR_CONF_NONE:
            return(-1);
        case VIR_CONF_LONG:
            virBufferVSprintf(buf, "%ld", val->l);
            break;
        case VIR_CONF_STRING:
            if (strchr(val->str, '\n') != NULL) {
                virBufferVSprintf(buf, "\"\"\"%s\"\"\"", val->str);
            } else if (strchr(val->str, '"') == NULL) {
                virBufferVSprintf(buf, "\"%s\"", val->str);
            } else if (strchr(val->str, '\'') == NULL) {
                virBufferVSprintf(buf, "'%s'", val->str);
            } else {
                virBufferVSprintf(buf, "\"\"\"%s\"\"\"", val->str);
            }
            break;
        case VIR_CONF_LIST: {
            virConfValuePtr cur;

            cur = val->list;
            virBufferAddLit(buf, "[ ");
            if (cur != NULL) {
                virConfSaveValue(buf, cur);
                cur = cur->next;
                while (cur != NULL) {
                    virBufferAddLit(buf, ", ");
                    virConfSaveValue(buf, cur);
                    cur = cur->next;
                }
            }
            virBufferAddLit(buf, " ]");
            break;
        }
        default:
            return(-1);
    }
    return(0);
}

/**
 * virConfSaveEntry:
 * @buf: output buffer
 * @cur: a conf entry
 *
 * Serialize the entry to the buffer
 *
 * Returns 0 in case of success, -1 in case of error.
 */
static int
virConfSaveEntry(virBufferPtr buf, virConfEntryPtr cur)
{
    if (cur->name != NULL) {
        virBufferAdd(buf, cur->name, -1);
        virBufferAddLit(buf, " = ");
        virConfSaveValue(buf, cur->value);
        if (cur->comment != NULL) {
            virBufferAddLit(buf, " #");
            virBufferAdd(buf, cur->comment, -1);
        }
    } else if (cur->comment != NULL) {
        virBufferAddLit(buf, "#");
        virBufferAdd(buf, cur->comment, -1);
    }
    virBufferAddLit(buf, "\n");
    return(0);
}

/************************************************************************
 *									*
 *			The parser core					*
 *									*
 ************************************************************************/

/**
 * virConfParseLong:
 * @ctxt: the parsing context
 * @val: the result
 *
 * Parse one long int value
 *
 * Returns 0 in case of success and -1 in case of error
 */
static int
virConfParseLong(virConfParserCtxtPtr ctxt, long *val)
{
    long l = 0;
    int neg = 0;

    if (CUR == '-') {
        neg = 1;
        NEXT;
    } else if (CUR == '+') {
        NEXT;
    }
    if ((ctxt->cur >= ctxt->end) || (!c_isdigit(CUR))) {
        virConfError(ctxt, VIR_ERR_CONF_SYNTAX, _("unterminated number"));
        return(-1);
    }
    while ((ctxt->cur < ctxt->end) && (c_isdigit(CUR))) {
        l = l * 10 + (CUR - '0');
        NEXT;
    }
    if (neg)
        l = -l;
    *val = l;
    return(0);
}

/**
 * virConfParseString:
 * @ctxt: the parsing context
 *
 * Parse one string
 *
 * Returns a pointer to the string or NULL in case of error
 */
static char *
virConfParseString(virConfParserCtxtPtr ctxt)
{
    const char *base;
    char *ret = NULL;

    if (CUR == '\'') {
        NEXT;
        base = ctxt->cur;
        while ((ctxt->cur < ctxt->end) && (CUR != '\'') && (!IS_EOL(CUR)))
            NEXT;
        if (CUR != '\'') {
            virConfError(ctxt, VIR_ERR_CONF_SYNTAX, _("unterminated string"));
            return(NULL);
        }
        ret = strndup(base, ctxt->cur - base);
        NEXT;
    } else if ((ctxt->cur + 6 < ctxt->end) && (ctxt->cur[0] == '"') &&
               (ctxt->cur[1] == '"') && (ctxt->cur[2] == '"')) {
        ctxt->cur += 3;
        base = ctxt->cur;
        while ((ctxt->cur + 2 < ctxt->end) && (ctxt->cur[0] == '"') &&
               (ctxt->cur[1] == '"') && (ctxt->cur[2] == '"')) {
               if (CUR == '\n') ctxt->line++;
               NEXT;
        }
        if ((ctxt->cur[0] != '"') || (ctxt->cur[1] != '"') ||
            (ctxt->cur[2] != '"')) {
            virConfError(ctxt, VIR_ERR_CONF_SYNTAX, _("unterminated string"));
            return(NULL);
        }
        ret = strndup(base, ctxt->cur - base);
        ctxt->cur += 3;
    } else if (CUR == '"') {
        NEXT;
        base = ctxt->cur;
        while ((ctxt->cur < ctxt->end) && (CUR != '"') && (!IS_EOL(CUR)))
            NEXT;
        if (CUR != '"') {
            virConfError(ctxt, VIR_ERR_CONF_SYNTAX, _("unterminated string"));
            return(NULL);
        }
        ret = strndup(base, ctxt->cur - base);
        NEXT;
    }
    return(ret);
}

/**
 * virConfParseValue:
 * @ctxt: the parsing context
 *
 * Parse one value
 *
 * Returns a pointer to the value or NULL in case of error
 */
static virConfValuePtr
virConfParseValue(virConfParserCtxtPtr ctxt)
{
    virConfValuePtr ret, lst = NULL, tmp, prev;
    virConfType type = VIR_CONF_NONE;
    char *str = NULL;
    long  l = 0;

    SKIP_BLANKS;
    if (ctxt->cur >= ctxt->end) {
        virConfError(ctxt, VIR_ERR_CONF_SYNTAX, _("expecting a value"));
        return(NULL);
    }
    if ((CUR == '"') || (CUR == '\'')) {
        type = VIR_CONF_STRING;
        str = virConfParseString(ctxt);
        if (str == NULL)
            return(NULL);
    } else if (CUR == '[') {
        type = VIR_CONF_LIST;
        NEXT;
        SKIP_BLANKS_AND_EOL;
        if ((ctxt->cur < ctxt->end) && (CUR != ']')) {
            if ((lst = virConfParseValue(ctxt)) == NULL)
                return(NULL);
            SKIP_BLANKS_AND_EOL;
        }
        while ((ctxt->cur < ctxt->end) && (CUR != ']')) {
            if (CUR != ',') {
                virConfError(ctxt, VIR_ERR_CONF_SYNTAX,
                             _("expecting a separator in list"));
                virConfFreeList(lst);
                return(NULL);
            }
            NEXT;
            SKIP_BLANKS_AND_EOL;
            if (CUR == ']') {
                break;
            }
            tmp = virConfParseValue(ctxt);
            if (tmp == NULL) {
                virConfFreeList(lst);
                return(NULL);
            }
            prev = lst;
            while (prev->next != NULL) prev = prev->next;
            prev->next = tmp;
            SKIP_BLANKS_AND_EOL;
        }
        if (CUR == ']') {
            NEXT;
        } else {
            virConfError(ctxt, VIR_ERR_CONF_SYNTAX,
                         _("list is not closed with ]"));
            virConfFreeList(lst);
            return(NULL);
        }
    } else if (c_isdigit(CUR) || (CUR == '-') || (CUR == '+')) {
        if (virConfParseLong(ctxt, &l) < 0) {
            return(NULL);
        }
        type = VIR_CONF_LONG;
    } else {
        virConfError(ctxt, VIR_ERR_CONF_SYNTAX, _("expecting a value"));
        return(NULL);
    }
    if (VIR_ALLOC(ret) < 0) {
        virConfError(ctxt, VIR_ERR_NO_MEMORY, _("allocating configuration"));
        virConfFreeList(lst);
        VIR_FREE(str);
        return(NULL);
    }
    ret->type = type;
    ret->l = l;
    ret->str = str;
    ret->list = lst;
    return(ret);
}

/**
 * virConfParseName:
 * @ctxt: the parsing context
 *
 * Parse one name
 *
 * Returns a copy of the new string, NULL in case of error
 */
static char *
virConfParseName(virConfParserCtxtPtr ctxt)
{
    const char *base;
    char *ret;

    SKIP_BLANKS;
    base = ctxt->cur;
    /* TODO: probably need encoding support and UTF-8 parsing ! */
    if (!c_isalpha(CUR)) {
        virConfError(ctxt, VIR_ERR_CONF_SYNTAX, _("expecting a name"));
        return(NULL);
    }
    while ((ctxt->cur < ctxt->end) && (c_isalnum(CUR) || (CUR == '_')))
        NEXT;
    ret = strndup(base, ctxt->cur - base);
    if (ret == NULL) {
        virConfError(ctxt, VIR_ERR_NO_MEMORY, _("allocating configuration"));
        return(NULL);
    }
    return(ret);
}

/**
 * virConfParseComment:
 * @ctxt: the parsing context
 *
 * Parse one standalone comment in the configuration file
 *
 * Returns 0 in case of success and -1 in case of error
 */
static int
virConfParseComment(virConfParserCtxtPtr ctxt)
{
    const char *base;
    char *comm;

    if (CUR != '#')
        return(-1);
    NEXT;
    base = ctxt->cur;
    while ((ctxt->cur < ctxt->end) && (!IS_EOL(CUR))) NEXT;
    comm = strndup(base, ctxt->cur - base);
    if (comm == NULL) {
        virConfError(ctxt, VIR_ERR_NO_MEMORY, _("allocating configuration"));
        return(-1);
    }
    virConfAddEntry(ctxt->conf, NULL, NULL, comm);
    return(0);
}

/**
 * virConfParseSeparator:
 * @ctxt: the parsing context
 *
 * Parse one separator between statement if not at the end.
 *
 * Returns 0 in case of success and -1 in case of error
 */
static int
virConfParseSeparator(virConfParserCtxtPtr ctxt)
{
    SKIP_BLANKS;
    if (ctxt->cur >= ctxt->end)
        return(0);
    if (IS_EOL(CUR)) {
        SKIP_BLANKS_AND_EOL;
    } else if (CUR == ';') {
        NEXT;
        SKIP_BLANKS_AND_EOL;
    } else {
        virConfError(ctxt, VIR_ERR_CONF_SYNTAX, _("expecting a separator"));
        return(-1);
    }
    return(0);
}

/**
 * virConfParseStatement:
 * @ctxt: the parsing context
 *
 * Parse one statement in the conf file
 *
 * Returns 0 in case of success and -1 in case of error
 */
static int
virConfParseStatement(virConfParserCtxtPtr ctxt)
{
    const char *base;
    char *name;
    virConfValuePtr value;
    char *comm = NULL;

    SKIP_BLANKS_AND_EOL;
    if (CUR == '#') {
        return(virConfParseComment(ctxt));
    }
    name = virConfParseName(ctxt);
    if (name == NULL)
        return(-1);
    SKIP_BLANKS;
    if (CUR != '=') {
        virConfError(ctxt, VIR_ERR_CONF_SYNTAX, _("expecting an assignment"));
        return(-1);
    }
    NEXT;
    SKIP_BLANKS;
    value = virConfParseValue(ctxt);
    if (value == NULL) {
        VIR_FREE(name);
        return(-1);
    }
    SKIP_BLANKS;
    if (CUR == '#') {
        NEXT;
        base = ctxt->cur;
        while ((ctxt->cur < ctxt->end) && (!IS_EOL(CUR))) NEXT;
        comm = strndup(base, ctxt->cur - base);
        if (comm == NULL) {
            virConfError(ctxt, VIR_ERR_NO_MEMORY, _("allocating configuration"));
            VIR_FREE(name);
            virConfFreeValue(value);
            return(-1);
        }
    }
    if (virConfAddEntry(ctxt->conf, name, value, comm) == NULL) {
        VIR_FREE(name);
        virConfFreeValue(value);
        VIR_FREE(comm);
        return(-1);
    }
    return(0);
}

/**
 * virConfParse:
 * @filename: the name to report errors
 * @content: the configuration content in memory
 * @len: the length in bytes
 *
 * Parse the subset of the Python language needed to handle simple
 * Xen configuration files.
 *
 * Returns an handle to lookup settings or NULL if it failed to
 *         read or parse the file, use virConfFree() to free the data.
 */
static virConfPtr
virConfParse(const char *filename, const char *content, int len) {
    virConfParserCtxt ctxt;

    ctxt.filename = filename;
    ctxt.base = ctxt.cur = content;
    ctxt.end = content + len - 1;
    ctxt.line = 1;

    ctxt.conf = virConfCreate(filename);
    if (ctxt.conf == NULL)
        return(NULL);

    while (ctxt.cur < ctxt.end) {
        if (virConfParseStatement(&ctxt) < 0)
            goto error;
        if (virConfParseSeparator(&ctxt) < 0)
            goto error;
    }

    return(ctxt.conf);

error:
    virConfFree(ctxt.conf);
    return(NULL);
}

/************************************************************************
 *									*
 *			The module entry points				*
 *									*
 ************************************************************************/

/* 10 MB limit on config file size as a sanity check */
#define MAX_CONFIG_FILE_SIZE (1024*1024*10)

/**
 * virConfReadFile:
 * @filename: the path to the configuration file.
 *
 * Reads a configuration file.
 *
 * Returns an handle to lookup settings or NULL if it failed to
 *         read or parse the file, use virConfFree() to free the data.
 */
virConfPtr
virConfReadFile(const char *filename)
{
    char *content;
    int len;
    virConfPtr conf;

    if (filename == NULL) {
        virConfError(NULL, VIR_ERR_INVALID_ARG, __FUNCTION__);
        return(NULL);
    }

    if ((len = virFileReadAll(filename, MAX_CONFIG_FILE_SIZE, &content)) < 0) {
        return NULL;
    }

    conf = virConfParse(filename, content, len);

    VIR_FREE(content);

    return conf;
}

/**
 * virConfReadMem:
 * @memory: pointer to the content of the configuration file
 * @len: length in byte
 *
 * Reads a configuration file loaded in memory. The string can be
 * zero terminated in which case @len can be 0
 *
 * Returns an handle to lookup settings or NULL if it failed to
 *         parse the content, use virConfFree() to free the data.
 */
virConfPtr
virConfReadMem(const char *memory, int len)
{
    if ((memory == NULL) || (len < 0)) {
        virConfError(NULL, VIR_ERR_INVALID_ARG, __FUNCTION__);
        return(NULL);
    }
    if (len == 0)
        len = strlen(memory);

    return(virConfParse("memory conf", memory, len));
}

/**
 * virConfFree:
 * @conf: a configuration file handle
 *
 * Frees all data associated to the handle
 *
 * Returns 0 in case of success, -1 in case of error.
 */
int
virConfFree(virConfPtr conf)
{
    virConfEntryPtr tmp;
    if (conf == NULL) {
        virConfError(NULL, VIR_ERR_INVALID_ARG, __FUNCTION__);
        return(-1);
    }

    tmp = conf->entries;
    while (tmp) {
        virConfEntryPtr next;
        VIR_FREE(tmp->name);
        virConfFreeValue(tmp->value);
        VIR_FREE(tmp->comment);
        next = tmp->next;
        VIR_FREE(tmp);
        tmp = next;
    }
    VIR_FREE(conf);
    return(0);
}

/**
 * virConfGetValue:
 * @conf: a configuration file handle
 * @entry: the name of the entry
 *
 * Lookup the value associated to this entry in the configuration file
 *
 * Returns a pointer to the value or NULL if the lookup failed, the data
 *         associated will be freed when virConfFree() is called
 */
virConfValuePtr
virConfGetValue(virConfPtr conf, const char *setting)
{
    virConfEntryPtr cur;

    cur = conf->entries;
    while (cur != NULL) {
        if ((cur->name != NULL) && (STREQ(cur->name, setting)))
            return(cur->value);
        cur = cur->next;
    }
    return(NULL);
}

/**
 * virConfSetValue:
 * @conf: a configuration file handle
 * @entry: the name of the entry
 * @value: the new configuration value
 *
 * Set (or replace) the value associated to this entry in the configuration
 * file. The passed in 'value' will be owned by the conf object upon return
 * of this method, even in case of error. It should not be referenced again
 * by the caller.
 *
 * Returns 0 on success, or -1 on failure.
 */
int
virConfSetValue (virConfPtr conf,
                 const char *setting,
                 virConfValuePtr value)
{
    virConfEntryPtr cur, prev = NULL;

    cur = conf->entries;
    while (cur != NULL) {
        if ((cur->name != NULL) && (STREQ(cur->name, setting))) {
            break;
        }
        prev = cur;
        cur = cur->next;
    }

    if (!cur) {
        if (VIR_ALLOC(cur) < 0) {
            virConfFreeValue(value);
            return (-1);
        }
        cur->comment = NULL;
        if (!(cur->name = strdup(setting))) {
            virConfFreeValue(value);
            VIR_FREE(cur);
            return (-1);
        }
        cur->value = value;
        if (prev) {
            cur->next = prev->next;
            prev->next = cur;
        } else {
            cur->next = conf->entries;
            conf->entries = cur;
        }
    } else {
        if (cur->value) {
            virConfFreeValue(cur->value);
        }
        cur->value = value;
    }
    return (0);
}


/**
 * virConfWriteFile:
 * @filename: the path to the configuration file.
 * @conf: the conf
 *
 * Writes a configuration file back to a file.
 *
 * Returns the number of bytes written or -1 in case of error.
 */
int
virConfWriteFile(const char *filename, virConfPtr conf)
{
    virBuffer buf = VIR_BUFFER_INITIALIZER;
    virConfEntryPtr cur;
    int ret;
    int fd;
    char *content;
    unsigned int use;

    if (conf == NULL)
        return(-1);

    cur = conf->entries;
    while (cur != NULL) {
        virConfSaveEntry(&buf, cur);
        cur = cur->next;
    }

    if (virBufferError(&buf)) {
        virConfError(NULL, VIR_ERR_NO_MEMORY, _("allocate buffer"));
        return -1;
    }

    fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR );
    if (fd < 0) {
        char *tmp = virBufferContentAndReset(&buf);
        virConfError(NULL, VIR_ERR_WRITE_FAILED, _("failed to open file"));
        VIR_FREE(tmp);
        return -1;
    }

    use = virBufferUse(&buf);
    content = virBufferContentAndReset(&buf);
    ret = safewrite(fd, content, use);
    VIR_FREE(content);
    close(fd);
    if (ret != (int)use) {
        virConfError(NULL, VIR_ERR_WRITE_FAILED, _("failed to save content"));
        return -1;
    }

    return ret;
}

/**
 * virConfWriteMem:
 * @memory: pointer to the memory to store the config file
 * @len: pointer to the length in bytes of the store, on output the size
 * @conf: the conf
 *
 * Writes a configuration file back to a memory area. @len is an IN/OUT
 * parameter, it indicates the size available in bytes, and on output the
 * size required for the configuration file (even if the call fails due to
 * insufficient space).
 *
 * Returns the number of bytes written or -1 in case of error.
 */
int
virConfWriteMem(char *memory, int *len, virConfPtr conf)
{
    virBuffer buf = VIR_BUFFER_INITIALIZER;
    virConfEntryPtr cur;
    char *content;
    unsigned int use;

    if ((memory == NULL) || (len == NULL) || (*len <= 0) || (conf == NULL))
        return(-1);

    cur = conf->entries;
    while (cur != NULL) {
        virConfSaveEntry(&buf, cur);
        cur = cur->next;
    }

    if (virBufferError(&buf)) {
        virConfError(NULL, VIR_ERR_NO_MEMORY, _("allocate buffer"));
        return -1;
    }

    use = virBufferUse(&buf);
    content = virBufferContentAndReset(&buf);

    if ((int)use >= *len) {
        *len = (int)use;
        VIR_FREE(content);
        return -1;
    }
    memcpy(memory, content, use);
    VIR_FREE(content);
    *len = use;
    return use;
}