[ovirt-devel] What does SDM.merge's param "base_generation" in subchain_info means?

[pengyixiang]

hello, everyone!
     When we call "SDM.merge", we need a param "base_generation" in [1], and I know [2] will be called and "base_generation" is translated to "requested_gen", that means "GEN" in disk metadata?
If so, how did this "GEN" worked and seted? I see many *.meta is "GEN=0", and some is "GEN=1" in [3]. 




Hope to get your reply, Thank you!




[1]  {'subchain_info': {'img_id': '91837525-850d-4e74-9a7e-c89b793d0e5b', 'sd_id': '93b8a2c9-f527-4eb3-acfb-af76ab24fbbe', 'top_id': '4e51d4e5-9630-45a6-9829-012460e7d67a', 'base_id': 'fdf47584-21aa-45b2-9925-157ff54f5e7e', 'base_generation': 0}, 'job_id': '766a3050-476c-48ae-9470-3bec7867a6cd'}


[2]  https://github.com/oVirt/vdsm/blob/07d05287ac1496ad49915e026d34e29ca4da635b/lib/vdsm/storage/volume.py#L602


[3] 
DOMAIN=93b8a2c9-f527-4eb3-acfb-af76ab24fbbe CTIME=1516090454 FORMAT=COW DISKTYPE=2 LEGALITY=LEGAL SIZE=167772160 VOLTYPE=INTERNAL DESCRIPTION= IMAGE=f882e7cc-f57e-48ff-9b87-bba35331e983 PUUID=9050f956-6836-4fce-8d27-69df13c4f85c MTIME=0 POOL_UUID= TYPE=SPARSE GEN=1 EOF
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