Configurable storage path storage limit

[magik6k]

This adds a new MaxStorage field to sectorstore.json files, which allows setting maximum number of bytes to use in a storage path.

TODO:

• Test on a miner
• Add max-storage param to storage-attach commands

$ lotus-miner storage list
09b4f94d-b548-4382-92d1-551676289e3e:
        [###################################               ] 38.92 TiB/54.57 TiB 71%
        Unsealed: 180; Sealed: 867; Caches: 867; Reserved: 0 B
        Weight: 10; Use: Store
        Local: /data/1/store
        URL: http://[...]:2345/remote

92da064d-c2ee-4be1-802f-adbbabf1a06b:
        [#####################################             ] 1.367 TiB/1.818 TiB 75% (filesystem)
        [####################                              ] 64 GiB/153.6 GiB 41% (limit)
        Unsealed: 2; Sealed: 0; Caches: 0; Reserved: 0 B
        Weight: 10; Use: Seal 
        Local: /data/nvme/store
        URL: http://[...]:2345/remote

[arajasek]

LGTM

[arajasek]

So it's possible to have stat.Used > stat.Max, but that's fine, right? You just can't safely assume that Available + Used = Max?

[magik6k]

Correct