Re: [Xen-devel] [PATCH v2 09/18] libxl: disallow attaching the same device more than once

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Wed, 2014-07-30 at 19:23 +0100, Wei Liu wrote:
> Originally the code allowed users to attach the same device more than
> once. It just stupidly overwrites xenstore entries. This is bogus as
> frontend will be very confused.
> 
> Introduce a helper function to check if the device to be written to
> xenstore already exists. A new error code is also introduced.
> 
> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> ---
>  tools/libxl/libxl.c          |   50 
> ++++++++++++++++++++++++++++++++++++++++++
>  tools/libxl/libxl_device.c   |   19 ++++++++++++++++
>  tools/libxl/libxl_internal.h |    3 +++
>  tools/libxl/libxl_pci.c      |   12 ++++++++++
>  tools/libxl/libxl_types.idl  |    1 +
>  5 files changed, 85 insertions(+)
> 
> diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
> index 01dffa0..e6fe238 100644
> --- a/tools/libxl/libxl.c
> +++ b/tools/libxl/libxl.c
> @@ -1906,6 +1906,15 @@ void libxl__device_vtpm_add(libxl__egc *egc, uint32_t 
> domid,
>      rc = libxl__device_from_vtpm(gc, domid, vtpm, device);
>      if ( rc != 0 ) goto out;
>  
> +    rc = libxl__device_exists(gc, XBT_NULL, device);

Do we hold any locks from here until the code which actually creates the
device? I don't think we have an active transaction either which would
serve a similar purpose.

Otherwise can't another thread come and create another device after the
check and similarly confuse us?

(likewise for the other cases).

Ian.



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