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

From: Aneesh Kumar K.V
Subject: Re: [Qemu-devel] [PATCH 1/3] 9pfs-proxy: simplify error handling
Date: Tue, 10 Mar 2015 23:11:37 +0530
User-agent: Notmuch/0.19+30~gd241a48 (http://notmuchmail.org) Emacs/24.3.1 (x86_64-pc-linux-gnu)

Michael Tokarev <address@hidden> writes:

> 08.03.2015 19:27, Aneesh Kumar K.V wrote:
>> Michael Tokarev <address@hidden> 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

> 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.


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