Statfs.BlockSize() is returning an incorrect value

[ncw]

An rclone user reported that the free/used/total sizes were half what they should be in the smb backend: rclone/rclone#6733

I have verified this against this docker image https://hub.docker.com/r/dperson/samba and also that if you mount that disk from Windows it gets the free/used/total sizes correct.

Putting in a bit of debugging I see the Statfs block is returned as

stat{
    TotalAllocationUnits: 959122528,
    CallerAvailableAllocationUnits: 407504932,
    ActualAvailableAllocationUnits: 407504932,
    SectorsPerAllocationUnit: 2,
    BytesPerSector: 512,
}

Wheras the BlockSize is calculated like this

go-smb2/client.go

Lines 1438 to 1440 in c8e61c7

	func (fi *fileFsFullSizeInformation) BlockSize() uint64 {
	return uint64(fi.BytesPerSector)
	}

I suspect it should be calculated like this instead - this would make the sizes come out correctly.

func (fi *fileFsFullSizeInformation) BlockSize() uint64 {
	return uint64(fi.BytesPerSector) * uint64(fi.SectorsPerAllocationUnit)
}

However I have no knowledge of the SMB protocol so that might be completely wrong.

If you think that is good then I can make a PR with that in.