Re: [Xen-devel] Regarding Xenstore/Xenbus

["Umar Farooq Minhas" <umarfm13@xxxxxxxxxxx>]

Once again thanks for replying, I appreciate your patience.

Actually I already realized that mistake and replaced "daemon_open" with 
"domain_open".
But getting the "unknown error" has now changed into a "segmentation fault" 
and apparently
it occurs after i execute the "xs_directory" function to get the path in 
buf2 variable (line31 below).
I checked the value of 'len' variable after the call and it turns out to be 
arbitrarily large.
What am I doing wrong here ? After replacing "daemon_open" with 
"domain_open" all the rest
of the calls to xs.h functions remain the same or are there specific 
"daemon" and "domain"
versions of functions? (apparently its the former case)

A few related questions:

-Are there any specific initializations/calls that need to be made from 
inside domU to first initialize
and then access xenstore ? Or the functions exposed by xs.h are the only 
thing required ? Apparently
xenstore is initialized by dom0 once at startup only.

-Does ability to communicate with xenstore depend on whether the ethernet 
interface b/w
dom0 and domU is working or not (since it uses sockets)? Currently my domU 
can't ping dom0 or any one else
for that matter.

-I am trying to only read the xenstore(which is allowed to all domains by 
default), does my problem
in anyway relate to xenstore access permissions ?

-Are you aware of any user-space management tools available that access 
xenstore from within domU?
Sorry for a detailed mail but I am just a beginner and dont know a lot of 
stuff.
I'll appreciate your help once again.


-------------------------------------------------------------------------------------------

1   #include <xs.h>
2   #include <sys/types.h>
3   #include <stdio.h>
4   #include <string.h>
5
6   void main(int argc, char *argv[])
7   {
8
9      struct xs_handle *xs;
10     xs_transaction_t th;
11     char *path;
12     int fd;
13     fd_set set;
14     int er;
15     struct timeval tv = {.tv_sec = 0, .tv_usec = 0 };
16     char **vec;
17     unsigned int num;
18     char * buf;
19     char ** buf2;
20     unsigned int len;
21
22     unsigned int domid;
23
24     printf("Msg1\n");
25
26     /* Get a connection to the daemon */
27     xs = xs_domain_open();
28     if ( xs == NULL ) error();
29
30     th = xs_transaction_start(xs);
31         buf2 = xs_directory(xs, th,"/local/domain", &len);
32     xs_transaction_end(xs, th, true);
33
34     int i=0;
35
36     for(i=0;i<len;i++)
37     {
38         printf("%s\n",buf2[i]);
39     }
40
41
42  // I am running dom0 and oly 1 domU so this condition chooses one of 
them
43     if(len>1)
44         domid = atoi(buf2[1]);
45     if(len==1)
46         domid = atoi(buf2[0]);
47         //sprintf( domid, "%ui", buf2[0] );
48
49     printf("Domid: %i\n", domid);
50
51     /* Get the local domain path */
52     path = xs_get_domain_path(xs, domid);
53     if ( path == NULL ) error();
54
55     printf("Msg3\n");
56
57     /* Make space for our node on the path */
58     path = realloc(path, strlen(path) + strlen("/memory/target") + 1);
59     if ( path == NULL ) error();
60     strcat(path, "/memory/target");
61
62     /* Create a watch on /local/domain/%d/mynode. */
63     er = xs_watch(xs, path, "mytoken");
64     if ( er == 0 ) error();
65
66     /* We are notified of read availability on the watch via the
67      * file descriptor.
68      */
69     fd = xs_fileno(xs);
70
71     while (1)
72     {
73         FD_ZERO(&set);
74         FD_SET(fd, &set);
75
76         /* Poll for data. */
77         if ( select(fd + 1, &set, NULL, NULL, &tv) > 0
78              && FD_ISSET(fd, &set))
79         {
80             /* I am not sure how num works -- please describe. */
81             vec = xs_read_watch(xs, &num);
82             if ( !vec ) error();
83             printf("vec contents: %s|%s\n", vec[XS_WATCH_PATH],
84                                             vec[XS_WATCH_TOKEN]);
85
86             /* Prepare a transaction and do a read. */
87             th = xs_transaction_start(xs);
88                 buf = xs_read(xs, th, vec[XS_WATCH_PATH], &len);
89             xs_transaction_end(xs, th, true);
90             if ( buf )
91             {
92                 printf("buflen: %d\nbuf: %s\n", len, buf);
93             }
94
95             /* Prepare a transaction and do a write. */
96             /*th = xs_transaction_start(xs);
97
98  er = xs_write(xs, th, path, "somestuff", strlen("somestuff"));
99             xs_transaction_end(xs, th, true);
100            if ( er == 0 ) error();*/
101        }
102    }
103
104    /* Cleanup */
105    close(fd);
106    xs_daemon_close(xs);
107    free(path);
108
109 }
----- Original Message ----- 
From: "Vincent Hanquez" <vincent@xxxxxxxxxxxxx>
To: "Umar Farooq Minhas" <umarfm13@xxxxxxxxxxx>
Cc: <aball@xxxxxxxxxxxxxxxxxx>; <xen-devel@xxxxxxxxxxxxxxxxxxx>
Sent: Wednesday, November 22, 2006 10:52 AM
Subject: Re: [Xen-devel] Regarding Xenstore/Xenbus


> On Mon, Nov 20, 2006 at 08:21:20PM -0500, Umar Farooq Minhas wrote:
> > 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.
> you need to use "domain_open" instead of "daemon_open" in domU.
>
> daemon_open is using a direct unix socket to communicate with xenstored.
> this socket is only accessible to dom0. domU need to use the other way
> to communicate with xenstored.
>
> Cheers,
> --
> Vincent Hanquez

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel