Re: [Xen-devel] [PATCH] oxenstored: fix short-write issue

[David Scott <dave@xxxxxxxxxx>]

> On 27 Oct 2015, at 17:31, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> 
> On 27/10/15 17:28, Samuel Thibault wrote:
>> Andrew Cooper, le Tue 27 Oct 2015 17:21:39 +0000, a écrit :
>>> as the second attempted write could return short as well.
>> That is fine. The second attempt will only return a short write if there
>> was really not enough room for it, which is what we want.
> 
> Then surely the bug is that Xs_ring.write returns short when it shouldn’t?


> On 27 Oct 2015, at 17:31, Samuel Thibault <samuel.thibault@xxxxxxxxxxxx> 
> wrote:
> 
> Another way would be to make ml_interface_write write both pieces
> instead of just a contiguous one.  The caml code would then look less
> suspicious :)
> 

I agree with both Andrew and Samuel that it would be a better fix if 
Xs_ring.write (== “ml_interface_write”) wrote both pieces at once.

However I believe the ‘suspicious’ OCaml patch fixes the specific issue (— or 
have I missed something?).

Last time I meddled with the C-level ring reading/writing code I didn’t get it 
quite right. Does anyone have time to prototype what a C-level fix would look 
like? If we’re short of time I could live with the OCaml-level fix, especially 
since Wei has done some stress-testing (assuming everyone believes it fixes the 
issue)

Cheers,
Dave
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