[RFE] expose btrfs device stats

[jelly]

Btrfs exposes records device statistics via btrfs device stats (json or not) or via an ioctl BTRFS_IOC_GET_DEV_STATS. The stats can be obtained unprivileged.

The use case would be exposing these stats in Cockpit's btrfs device view:

I can imagine something like:

BlockDev.btrfs_filesystem_stats(mount_point)

The only question is how this will be integrated in UDisks, the API is based on a Filesystem so it could be. But that can be solved later, it could also become a part of org.freedesktop.UDisks2.Manager.BTRFS.

Regarding the implementation I am open to either using the ioctl in libblockdev or btrfs --format json device stats / (see output below). I am happy to implement either:

[jelle@homeserver ~]$ btrfs --format json device stats /mnt/disk
{
  "__header": {
    "version": "1"
  },
  "device-stats": [
    {
      "device": "/dev/sda",
      "devid": 1,
      "write_io_errs": 0,
      "read_io_errs": 0,
      "flush_io_errs": 0,
      "corruption_errs": 0,
      "generation_errs": 0
    },
    {
      "device": "/dev/sdb",
      "devid": 2,
      "write_io_errs": 0,
      "read_io_errs": 0,
      "flush_io_errs": 0,
      "corruption_errs": 0,
      "generation_errs": 0
    }
  ]
}

[tbzatek]

either using the ioctl in libblockdev or

I would prefer an ioctl if the return structure to parse is rather easy. And later to be ported over to libbtrfsutil? (#552)

The only question is how this will be integrated in UDisks, the API is based on a Filesystem so it could be. But that can be solved later, it could also become a part of org.freedesktop.UDisks2.Manager.BTRFS.

Well, that's an unfinished story, requiring lot of work: storaged-project/udisks#1232
Now that we have AI things may move faster, incl. the first design. Whether we're allowed to spend our time on that is another question.

Either way, I would suggest to make things right from the beginning. If we are to model volumes independently of block devices, then the UDisks btrfs module should be extended to provide new type of objects on the D-Bus object manager to represent volumes - i.e. org.freedesktop.UDisks2.Filesystem.BTRFSVolume as suggested in storaged-project/udisks#1232. That's still quite a lot of work.

My concern is whatever new method you'd introduce to the org.freedesktop.UDisks2.Manager.BTRFS interface, it would get deprecated once the new object model is introduced, creating further maintenance burden.

[jelly]

Having read the btrfs-progs code, the ioctl expects a device ID as input. This is already exposed via BtrfsDeviceInfo but as far as I can see not in UDisks.