Thanks for your reply. I was into trying out xenstore acess using
'libxenstore.so'. I have copied the exact code that I am trying to run (most
of this comes from xenstore wiki). The issue is that I am able to run this
code from dom0 but when I try to run it from inside a domU after the first
printf output i.e. "Msg1" it terminates abnormally saying "unknown error".
My guess is that its failing when it calls xs_daemon_open(). I can't figure
out what am i missing. Some processes need to be started before i can acess
xenstore? Are there any packages that need to be installed in domU to access
xenstore? I already have 'xen-devel', 'xen-lib' and 'xen-tools' packages
installed inside domU. Please help.
-------------------------------------------------------------------------------------------
#include <xs.h>
#include <sys/types.h>
#include <stdio.h>
#include <string.h>
void main(int argc, char *argv[])
{
struct xs_handle *xs;
xs_transaction_t th;
char *path;
int fd;
fd_set set;
int er;
struct timeval tv = {.tv_sec = 0, .tv_usec = 0 };
char **vec;
unsigned int num;
char * buf;
char ** buf2;
unsigned int len;
unsigned int domid;
printf("Msg1\n");
/* Get a connection to the daemon */
xs = xs_daemon_open();
if ( xs == NULL ) error();
th = xs_transaction_start(xs);
buf2 = xs_directory(xs, th,"/local/domain", &len);
xs_transaction_end(xs, th, true);
int i=0;
for(i=0;i<len;i++)
{
printf("%s\n",buf2[i]);
}
// I am running dom0 and oly 1 domU so this condition chooses one of
them
if(len>1)
domid = atoi(buf2[1]);
if(len==1)
domid = atoi(buf2[0]);
//sprintf( domid, "%ui", buf2[0] );
printf("Domid: %i\n", domid);
/* Get the local domain path */
path = xs_get_domain_path(xs, domid);
if ( path == NULL ) error();
printf("Msg3\n");
/* Make space for our node on the path */
path = realloc(path, strlen(path) + strlen("/memory/target") + 1);
if ( path == NULL ) error();
strcat(path, "/memory/target");
/* Create a watch on /local/domain/%d/mynode. */
er = xs_watch(xs, path, "mytoken");
if ( er == 0 ) error();
/* We are notified of read availability on the watch via the
* file descriptor.
*/
fd = xs_fileno(xs);
while (1)
{
FD_ZERO(&set);
FD_SET(fd, &set);
/* Poll for data. */
if ( select(fd + 1, &set, NULL, NULL, &tv) > 0
&& FD_ISSET(fd, &set))
{
/* I am not sure how num works -- please describe. */
vec = xs_read_watch(xs, &num);
if ( !vec ) error();
printf("vec contents: %s|%s\n", vec[XS_WATCH_PATH],
vec[XS_WATCH_TOKEN]);
/* Prepare a transaction and do a read. */
th = xs_transaction_start(xs);
buf = xs_read(xs, th, vec[XS_WATCH_PATH], &len);
xs_transaction_end(xs, th, true);
if ( buf )
{
printf("buflen: %d\nbuf: %s\n", len, buf);
}
/* Prepare a transaction and do a write. */
/*th = xs_transaction_start(xs);
er = xs_write(xs, th, path, "somestuff",
strlen("somestuff"));
xs_transaction_end(xs, th, true);
if ( er == 0 ) error();*/
}
}
/* Cleanup */
close(fd);
xs_daemon_close(xs);
free(path);
}
-------------------------------------------------------------------------------------------
----- Original Message -----
From: "Andrew D. Ball" <aball@xxxxxxxxxxxxxxxxxx>
To: "Umar Farooq Minhas" <umarfm13@xxxxxxxxxxx>
Cc: <xen-devel@xxxxxxxxxxxxxxxxxxx>
Sent: Monday, November 20, 2006 5:02 PM
Subject: Re: [Xen-devel] Regarding Xenstore/Xenbus
I think that's right. Look into using libxenstore inside of the domU --
I think there are functions to do what you want there.
Peace.
Andrew
On Sun, 2006-11-19 at 03:09 -0500, Umar Farooq Minhas wrote:
Hi everyone,
I have installed Xen on OpenSUSE Linux 10.1 and am just starting to
develop with Xen. I want to implement a very straightforward
application in domUs which simply gets notified whenever a resource
provisioning change (specifically for cpu/memory allocation) is made
for that particular domU using for example xm mem-set. From the
readings that I have done so far it seems that since xenstore is a
shared database between all the domains which keeps track of domain
specific values(including values of allocated resources) and that it
can be accessed through xenbus from domUs so what I need to do is to
write a program that would access xenstore from withing that domU over
xenbus. Or more specifically I will have to register a 'watch' in
xenstore (just as the balloon driver does) to monitor memory values. I
don't know whether this is true or not. I would greatly appreciate if
someone could verify this understanding or point me in the right
direction. Also if this is true some pointers to start developing with
xenbus/xenstore would be very helpful.
A prompt response will be appreciated as I am running on a deadline :)
Thanks.
-Umar
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