Wouter, > Right. I think we're getting close to a good spec now, for this thing. > > One thing I've been thinking about that we might want to add: > > There may be cases where a server, in performing the required calls to > be able to handle a BLOCK_STATUS request, will end up with more > information than the client asked; e.g., if the client asked information > in the base:allocation context on an extent at offset X of length Y, > then the server might conceivably do an lseek(SEEK_DATA) and/or > lseek(SEEK_HOLE). The result of that call might be that the file offset > will now point to a location Z, where Z > (X+Y). > > Currently, our spec says "the sum of the *length* fields MUST not be > greater than the overall *length* of request". This means that in > essense, the server then has to throw away the information it has on the > range Z - (X + Y). In case a client was interested in that information, > that seems like a waste. I would therefore like to remove that > requirement, by rephrasing that "sum of the *length* fields" thing into > something along the following lines: > > In case the server returns N extents, the sum of the *length* fields > of the first N-1 extents MUST NOT be greater than the overall *length* > of the request. The final extent MAY exceed the length of the request > if the server has that information anyway as a side effect of looking > up the required information and wishes to share it. > > This would then result in the fact that the "length" field in the > BLOCK_STATUS command would be little more than a hint, since we're > saying that a server can return more data than requested (if it's > available anyway) and less data than requested (if it would be too > resource-intensive to provide all the information). Not sure whether all > that makes much sense anymore, but hey.
+1 > In addition, the combination of a server providing more information than > requested with a "REQ_ONE" flag and a length field of zero could be an > interesting way to enumerate a whole export, too. Essentially, we could > define that as a client saying "I'm interested in what the size of the > extent at offset X is, and what its properties are". Also +1 -- Alex Bligh
