[Xen-devel] Question Regarding xs_read()

["Timothy Hayes" <hayesti@xxxxxx>]

Hi everyone,

 

I'm making a user application that's going to run in Xen guests (both dom0 and domU) and each instance needs to read values from the VM's unique space in XenStore. The way I have done it is use the functions defined in <xs.h> using the xs_read function to read a value. In command line I'm able to use the xenstore-read program and simply pass an argument like 'domid' or 'vm' without having to specify an absolute path, it will read the value in /local/domain/DOMID/ and I don't need to worry about what the DOMID is. When I try to use this technique in the xs_read function, it returns NULL. It works fine if I give the absolute path, but I can't really do that dynamically since I don't know the DOMID ahead of time.

 

Basically I'm trying this:

 

struct xs_handle* xs;
xs_transaction_t t;

void* domid;

char temp[] = "domid";

 

xs = xs_daemon_open();

t = xs_transaction_start(xs);

domid = xs_read(xs, t, temp, NULL);

 

Could someone explain why this doesn't work or maybe let me know of an alternative way to read XenStore in a C application without using absolute paths?

 

Cheers!

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