Bug 1563621

Description of problem:
Opening bz as per https://bugzilla.redhat.com/show_bug.cgi?id=1544680#c13


$ sudo rados list-inconsistent-snapset 3.7f
{"epoch":79,"inconsistents":[]}

$ sudo rados list-inconsistent-obj 3.7f --format=json-pretty
{
    "epoch": 79,
    "inconsistents": [
        {
            "object": {
                "name": "obj1",
                "nspace": "",
                "locator": "",
                "snap": "head",
                "version": 13
            },
            "errors": [
                "snapset_inconsistency" 
            ],
            "union_shard_errors": [],
            "selected_object_info": "3:ff7b1f36:::obj1:head(73'13 client.4471.0:1 dirty|data_digest|omap_digest s 1682 uv 13 dd 735b0743 od ffffffff alloc_hint [0 0 0])",
            "shards": [
                {
                    "osd": 1,
                    "primary": false,
                    "errors": [],
                    "size": 1682,
                    "omap_digest": "0xffffffff",
                    "data_digest": "0x735b0743",
                    "snapset": "0=[]:[]+stray_clone_snaps={1=[1],2=[2],3=[3],4=[4],5=[5],6=[6]}" 
                },
                {
                    "osd": 6,
                    "primary": true,
                    "errors": [],
                    "size": 1682,
                    "omap_digest": "0xffffffff",
                    "data_digest": "0x735b0743",
                    "snapset": "6=[6,5,4,3,2,1]:{1=[1],2=[2],3=[3],4=[4],5=[5],6=[6]}" 
                },
                {
                    "osd": 8,
                    "primary": false,
                    "errors": [],
                    "size": 1682,
                    "omap_digest": "0xffffffff",
                    "data_digest": "0x735b0743",
                    "snapset": "6=[6,5,4,3,2,1]:{1=[1],2=[2],3=[3],4=[4],5=[5],6=[6]}" 
                }
            ]
        }
    ]
}
For now the user would have to increase the debug_osd log level and examine the osd logs to find the selected authoritative copy for a specific object. With 2 or different snapsets we could make it more complex by showing the snapshot results using each snapset for comparison or easier would be to indicate which is the authoritative copy. The existing code in PG::scrub_compare_maps() doesn't pass enough information to PrimaryLogPG::scrub_snapshot_metadata() for it to see both snapset variants or know which shard it is using.

Additional info: