9:06 a.m.
On Wed, Aug 23, 2006 at 05:15:26PM -0400, Daniel Veillard wrote:
On Wed, Aug 23, 2006 at 09:22:08PM +0100, Daniel P. Berrange wrote:
> On Wed, Aug 23, 2006 at 02:21:03PM -0400, Daniel Veillard wrote:
> > I was tempted to do an implementation just local to the library instance
> > in the case there is no support by the virtualization engine. If you think
> > you will use it then I should really implement it :-)
>
> Trouble is I think we really badly need an implementation that is
> persistent. Tools like the 'xeninst[1]' package are using libvirt for
> creating domains, but at the same time manually writing out config
> files into /etc/xen - this means they are loosing an important benefit
> of libvirt - namely isolation from Xen instability/changes.
>
> Now it would be pretty easy for libvirt to convert the XML file passed
> into virDefineDomain into a config file for xend & stuf it in /etc/xen
> The hard part is the reverse - enumerating the config files in the
> dir & turning them back into XML. I fear we may have to tackle that
[...]
> * Write a tiny parser for a trivial subset - basically enough
to
> handle the (key, string) pairs & (key, list of string) pairs.
> Certainly doable - depending on how general purpose we want to
> get - do we care about the 'if..else' conditional used in the
> sample /etc/xen/xmexample.vti config file ? We can certainly
> make a valid case saying we don't care about this because the
> libvirt XML -> xm config conversion would not generate config
> using that capability
I'm not too concerned by handling only a subset, this should be data
and processed as such IMHO.
> * Fork an unprivileged helper python program to exec the config
> file and re-write it as XML which can be read back in by libvirt
>
> The former is more work, but makes me feel better from a security
> point of view.
Writing a parser doesn't frighten me too much :-)
[...]
> Not a perfect solution, but would satisfy a great deal of
common
> use cases pretty easily without being intrusive into existing code
> base & pretty secure.
We are basically in agreement :-)
So I write that parser ?
Okay, there is a a first version in CVS under libvirt/src/conf.[ch]
It allows only variable assignments and comments, the types supported
are the [] lists, integers and strings. Still that should be sufficient
to handled most data oriented existing Python Xen configurations.
It supports load/lookup/writes as defined in conf.h:
-------------------------------------
typedef struct _virConf virConf;
typedef virConf *virConfPtr;
virConfPtr virConfReadFile (const char *filename);
virConfPtr virConfReadMem (const char *memory,
int len);
int virConfFree (virConfPtr conf);
virConfValuePtr virConfGetValue (virConfPtr conf,
const char *setting);
int virConfWriteFile (const char *filename,
virConfPtr conf);
int virConfWriteMem (char *memory,
int *len,
virConfPtr conf);
-------------------------------------
Values are open structures:
-------------------------------------
/**
* virConfType:
* one of the possible type for a value from the configuration file
*
* TODO: we probably need a float too.
*/
typedef enum {
VIR_CONF_NONE = 0, /* undefined */
VIR_CONF_LONG = 1, /* a long int */
VIR_CONF_STRING = 2, /* a string */
VIR_CONF_LIST = 3 /* a list */
} virConfType;
/**
* virConfValue:
* a value from the configuration file
*/
typedef struct _virConfValue virConfValue;
typedef virConfValue *virConfValuePtr;
struct _virConfValue {
virConfType type; /* the virConfType */
virConfValuePtr next; /* next element if in a list */
long l; /* long integer */
char *str; /* pointer to 0 terminated string */
virConfValuePtr list; /* list of a list */
};
-------------------------------------
If needed it's possible to lookup a value, change the object and save back,
I could extend the supported subset to handle expressions or reuse of variables
in assignments, but I'm not sure it is really worth it.
The parser is strict, if it meets a construct it doesn't recognize it fails
and return NULL with an error.
Daniel
--
Red Hat Virtualization group http://redhat.com/virtualization/
Daniel Veillard | virtualization library http://libvirt.org/
veillard(a)redhat.com | libxml GNOME XML XSLT toolkit http://xmlsoft.org/
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