Xen devel - Jan 2006 - Getting VBD working with xenstore, again

hi,

I have the code below, a version of which used to (just before xen3
release) work fine for giving my domain access to a block device. I
have tried to adjust this based on the python source, but my block
device no longer registers in domU :-(

For domU I am using the linux-2.6.12 from xen-unstable (about one week
old) and for dom0 linux-2.6-xen.hg of about the same age.

void setup_vbd(int domid, int uuid, char* vdev, char* pdev)
{
    struct xs_transaction_handle* t;

    struct xs_permissions xsperms[2];
    xsperms[0].id = domid;
    xsperms[0].perms = XS_PERM_READ | XS_PERM_WRITE;

    char s[256];
    char s2[256];

    char* home = xs_get_domain_path(xs,domid);
    char* dom0_home = xs_get_domain_path(xs,0);
    printf("dom0_home is %s\n",dom0_home);


    char backend[256];
    char frontend[256];
    sprintf(backend,"%s/backend/vbd/%d/%d",dom0_home,uuid,domid);
    sprintf(frontend, "%s/device/vbd/%d",home,uuid);

    xs_begin();

    sprintf(s,"%s/domain",backend);
    sprintf(s2,"%d",domid);
    xs_w(s, s2);

    sprintf(s,"%s/frontend",backend);
    xs_w(s, frontend );

    sprintf(s,"%s/frontend-id",backend);
    sprintf(s2,"%d",domid);
    xs_w(s, s2 );

    sprintf(s, "%s/state", backend);
    xs_w(s, "1");


    xs_end();

    xs_begin();
    xs_mkdir(xs,t,backend);
    int result = xs_set_permissions(xs, t, backend, xsperms, 1);

    sprintf(s,"%s/backend",frontend);
    xs_w(s, backend );

    sprintf(s, "%s/backend-id", frontend);
    xs_w(s, "0");

    sprintf(s, "%s/state", frontend);
    xs_w(s, "1");


    sprintf(s, "%s/virtual-device", frontend);
    xs_w(s, vdev );

    xs_end();
}

I hope someone can point out the obvious mistake in the code above.

Thanks in advance,
Jacob

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On 1/12/06, Jacob Gorm Hansen <jacobg@diku.dk>
wrote:
> hi,
>
> I have the code below, a version of which used to (just before xen3
> release) work fine for giving my domain access to a block device. I
> have tried to adjust this based on the python source, but my block
> device no longer registers in domU :-(
Got it working, main points was that I had to reverse the order of
writing to frontend and backend stores (probably not new actually),
that the physical-device string is now in "%x:%x" format (but the
virtual-device is not...) and that the the mode key is mandatory.

Best,
Jacob

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On Thu, Jan 12, 2006 at 03:42:12PM +0100, Jacob Gorm Hansen wrote:
> On 1/12/06, Jacob Gorm Hansen <jacobg@diku.dk> wrote:
> > hi,
> >
> > I have the code below, a version of which used to (just before xen3
> > release) work fine for giving my domain access to a block device. I
> > have tried to adjust this based on the python source, but my block
> > device no longer registers in domU :-(
> 
> Got it working, main points was that I had to reverse the order of
> writing to frontend and backend stores (probably not new actually),
You ought to be writing these entries in one transaction, so that they appear
atomically.  This will guarantee that you avoid any race conditions on
start-up.
> that the physical-device string is now in "%x:%x" format (but the
> virtual-device is not...)
My intention was to change virtual-device so that it was the name rather than
the device number -- there''s no reason for dom0''s device
numbers to be the
same as domU''s, as they may be different operating systems -- but it
didn''t
make it into 3.0, due to lack of time ;-(

Ewan.

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