Re: [Qemu-devel] [PATCH 1/3] 9pfs-proxy: simplify error handling

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

Michael Tokarev <mjt@tls.msk.ru> writes:

> 08.03.2015 19:27, Aneesh Kumar K.V wrote:
>> Michael Tokarev <mjt@tls.msk.ru> writes:
> []
>>> Actually, after reading almost whole 9pfs and fsdev code, I can
>>> say with great confidence this code is nearly hopeless.
>> 
>> Is that about the 9pfs-proxy code, or the rest of 9pfs. I understand
>
> Well. the marshal/unmarshal interface is in core code as far as
> I can see, and it is very fragile at best, as the below example of
> its usage shows.  I haven't dug deeper.  So far, it was only the
> 9pfs proxy code.

May be i am missing something here. Can you help me understand the
issue. 

> static int v9fs_receive_status(V9fsProxy *proxy,
>                                struct iovec *reply, int *status)
> ...
>     proxy_unmarshal(reply, 0, "dd", &header.type, &header.size);
>     if (header.size != sizeof(int)) {
>         *status = -ENOBUFS;
>     }
> ...
>     proxy_unmarshal(reply, PROXY_HDR_SZ, "d", status);
>
> proxy_unmarshall(), for "d" element, expects an int32_t
> pointer.  Here we have int pointer, and compare its
> size with sizeof(int).  This is a generic problem of whole
> v9fs_(un)marshall interface, which is in the core of 9pfs...
> this is a status return, which is int32.

Proxy helper do write sizeof(int) as a part of header response. So
it read the header.size and check whether it is same as what it is
expecting. If not it error out. So i am not sure what the issue you are
listing here.

-aneesh