Potential off-by-one in offset handling of TRIM command

[NicolasT]

While playing around with the "TRIM" support, I found it nothing happens when using offset 0 (using nbd-server). I think exptrim contains an off-by-one bug:

if(prev.startoff < req->from) {

should be

if(prev.startoff <= req->from) {

Although, that's my suspicion. Only confirmed to work for a single-file export.

[yoe]

Yes, you're right; that's an off-by-one.

I must admit that the TRIM code hasn't been tested much. I implemented it before the support for it was in the kernel, and my tester client doesn't try it...