[BUG] rbd discard should return OK even if rbd file does not exist

[Stefan Priebe <s.priebe@profihost.ag>]

Hello list,

right now librbd returns an error if i issue a discard for a sector / 
byterange where ceph does not have any file as i had never written to 
this section.

This is not correct. It should return 0 / OK in this case.

Stefan

Examplelog:
2012-11-02 21:06:17.649922 7f745f7fe700 20 librbd::AioRequest: WRITE_FLAT
2012-11-02 21:06:17.649924 7f745f7fe700 20 librbd::AioCompletion: 
AioCompletion::complete_request() this=0x7f72cc05bd20 
complete_cb=0x7f747021d4b0
2012-11-02 21:06:17.649924 7f747015c780  1 -- 10.10.0.2:0/2028325 --> 
10.10.0.18:6803/9687 -- osd_op(client.26862.0:3073 
rb.0.1044.359ed6c7.000000000bde [delete] 3.bd84636 snapc 2=[]) v4 -- ?+0 
0x7f72d81c69b0 con 0x7f74600dbf50
2012-11-02 21:06:17.649934 7f747015c780 20 librbd:  oid 
rb.0.1044.359ed6c7.000000000bdf 0~4194304 from [4156556288,4194304]
2012-11-02 21:06:17.649972 7f7465a6e700  1 -- 10.10.0.2:0/2028325 <== 
osd.1202 10.10.0.18:6806/9821 143 ==== osd_op_reply(1652 
rb.0.1044.359ed6c7.000000000652 [delete] ondisk = -2 (No such file or 
directory)) v4 ==== 130+0+0 (2964367729 0 0) 0x7f72dc0f0090 con 
0x7f74600e4350
2012-11-02 21:06:17.649994 7f745f7fe700 20 librbd::AioRequest: write 
0x7f74600feab0 should_complete: r = -2