Re: xenstored: Interaction bettwen SET_PERMS and transaction

[Juergen Gross <jgross@xxxxxxxx>]

On 24.02.23 16:00, Julien Grall wrote:
> Hi Juergen,
>
> For some internal purpose, I need to write a script that would do the following:
>
>    1) Start a transaction
>    2) Call GET_PERMS
>    3) Call SET_PERMS with the permission just retrieved
>    4) Commit the transaction
>
> (Don't ask why :))
>
> This was executed from dom0 on every nodes. In some cases, we noticed that 4) 
> would return -ENOSPC.
> When digging through the code, it looks like this is because 
> transaction_fix_domains() (now called acc_fix_domains()) will check that the 
> quota is correct.
> The domain is question were over its limit, but given this is called by dom0, I 
> would have expected that it should not never return -ENOSPC (note that a 
> SET_PERMS outside of a transaction would work, but this can't be used our case).
> Furthermore, the transaction is not changing any accounting. So I find a bit 
> strange that we would prevent it even if this was run from an unprivileged domain.
> Do you know if this issues would be fixed by your current rework?
>
> If not, then I think we at least want to skip the quota check if the domain is 
> privileged.
> For non-privileged domain, I am not entirely sure what to do. I was originally 
> thinking to check if cd->nbentry is 0 and then skip the quota check. But this 
> would allow a domain to remove a node and then replace by a new one (I think we 
> still want to forbid that).
> What do you think?
Patch sent. Could you please test it with your script?


Juergen

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