Wouter Verhelst <[email protected]> writes:
> On Sat, May 28, 2011 at 05:35:22PM +0100, Alex Bligh wrote:
>> Goswin,
>>
>> --On 28 May 2011 16:37:12 +0200 Goswin von Brederlow <[email protected]>
>> wrote:
>> > + not NBD_CMD_FLAG_FUA:
>> > a) reply when the data has been recieved
>> > b) reply when the data has been commited to cache (write() returned)
>> > c) reply when the data has been commited to physical medium
>>
>> You may do any of those. Provided you will write the data "eventually"
>> (i.e. when you receive a REQ_FLUSH or a disconnect).
>>
>> > For a+b how does one report write errors that only appear after
>> > the reply? Report them in the next FLUSH request?
>>
>> You don't. To be safe, I'd error every write (i.e. turn the medium
>> read only).
>
> I don't think errors that appear after the reply are possible in the
> case of b (they are in the case of a, obviously)? Or what am I missing?
Write returns when the data is in cache. If the physical disk fails on
the write you only get the error on the next fsync() call.
MfG
Goswin
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