Re: [Xen-devel] Why xs_domain_open() in fs_backend

[Tim Deegan <Tim.Deegan@xxxxxxxxxx>]

At 08:19 +0100 on 13 Oct (1286957982), Jiang, Yunhong wrote:
> Later I noticed that the fs-backend utilize xs_domain_open(), instead
> of xs_daemon_open(), to communicate with xenstore. grep
> "xs_domain_open", I noticed it is in fact only used in
> xenstore_client.c, (xl use it when xs_daemon_open failed, but I
> suspect if it is really tested), and the xenstore_client.c does not
> use watch feature at all.

xs_domain_open() is required for xenstore clients to work when they're
not in the same domain as xenstored (either because xenstore is in a
stub domain or because the client is not in dom0).  Removing it is
definitely wrong.

(IMHO xs_daemon_open() should be killed entirely, but there are some
dom0 kernels where the xs_domain_open() connection isn't allowed to send
XS_INTRODUCE commands.  That shouldn't make a difference here, though).

> Following simple patch make it work, but I'm not sure if it is the
> right method, will fs-backend run in other domain?

What does the change to ROOT_NODE do in this patch?  Any chance that it 
fixes the problem by itself? :)

Cheers,

Tim.

> Thanks
> --jyh
> 
> diff -r a33886146b45 tools/fs-back/fs-backend.c
> --- a/tools/fs-back/fs-backend.c    Fri Oct 08 11:41:57 2010 +0100
> +++ b/tools/fs-back/fs-backend.c    Wed Oct 13 15:10:22 2010 +0800
> @@ -462,7 +462,7 @@ int main(void)
>      sigaction(SIGUSR2, &act, NULL);
> 
>      /* Open the connection to XenStore first */
> -    xsh = xs_domain_open();
> +    xsh = xs_daemon_open();
>      assert(xsh != NULL);
>      xs_rm(xsh, XBT_NULL, ROOT_NODE);
>      /* Create watch node */
> diff -r a33886146b45 tools/fs-back/fs-backend.h
> --- a/tools/fs-back/fs-backend.h    Fri Oct 08 11:41:57 2010 +0100
> +++ b/tools/fs-back/fs-backend.h    Wed Oct 13 15:10:33 2010 +0800
> @@ -9,7 +9,7 @@
>  #include <xen/io/fsif.h>
>  #include "sys-queue.h"
> 
> -#define ROOT_NODE           "backend/vfs"
> +#define ROOT_NODE           "/local/domain/0/backend/vfs"
>  #define EXPORTS_SUBNODE     "exports"
>  #define EXPORTS_NODE        ROOT_NODE"/"EXPORTS_SUBNODE
>  #define WATCH_NODE          EXPORTS_NODE"/requests"
> ~
> ~
> 
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-- 
Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, XenServer Engineering
Citrix Systems UK Ltd.  (Company #02937203, SL9 0BG)

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