Re: [PATCH 1/2] xen: xenbus_dev_frontend: Fix XS_TRANSACTION_END handling

[Juergen Gross]

On 12/02/18 09:49, Juergen Gross wrote:
> On 07/02/18 23:22, Simon Gaiser wrote:
>> Commit fd8aa9095a95 ("xen: optimize xenbus driver for multiple
>> concurrent xenstore accesses") made a subtle change to the semantic of
>> xenbus_dev_request_and_reply() and xenbus_transaction_end().
>>
>> Before on an error response to XS_TRANSACTION_END
>> xenbus_dev_request_and_reply() would not decrement the active
>> transaction counter. But xenbus_transaction_end() has always counted the
>> transaction as finished regardless of the response.
> 
> Which is correct now. Xenstore will free all transaction related
> data regardless of the response. A once failed transaction can't
> be repaired, it has to be repeated completely.
> 
> The real problem is decrementing the counter when XS_TRANSACTION_END
> for a non-existing transaction is being sent.
> 
>> The new behavior is that xenbus_dev_request_and_reply() and
>> xenbus_transaction_end() will always count the transaction as finished
>> regardless the response code (handled in xs_request_exit()).
> 
> ENOENT should not decrement the transaction counter, while all
> other responses to XS_TRANSACTION_END should still do so.

Sorry, I stand corrected: the ENOENT case should never happen, as this
case is tested in xenbus_write_transaction(). It doesn't hurt to test
for ENOENT, though.

What should be handled is EINVAL: this would happen if a user specified
a string different from "T" and "F".


Juergen