On Fri, 16 Jul 2021, Josef Bacik wrote: > > I'm going to restate what I think the problem is you're having just so I'm sure > we're on the same page. > > 1. We export a btrfs volume via nfsd that has multiple subvolumes. > 2. We run find, and when we stat a file, nfsd doesn't send along our bogus > st_dev, it sends it's own thing (I assume?). This confuses du/find because you > get the same inode number with different parents. > > Is this correct? If that's the case then it' be relatively straightforward to > add another callback into export_operations to grab this fsid right? Hell we > could simply return the objectid of the root since that's unique across the > entire file system. We already do our magic FH encoding to make sure we keep > all this straight for NFS, another callback to give that info isn't going to > kill us. Thanks, Fairly close. As well as the fsid I need a "mounted-on" inode number, so one callback to provide both would do. If zero was reported, that would be equivalent to not providing the callback. - Is "u64" always enough for the subvol-id? - Should we make these details available to user-space with a new STATX flag? - Should it be a new export_operations callback, or new fields in "struct kstat" ?? ... though having asked those question, I begin to wonder if I took a wrong turn. I can already get some fsid information form statfs, though it is only 64bits and for BTRFS is combines the filesystem uuid and the subvol id. For that reason I avoided it. But I'm already caching the fsid for the export-point. If, when I find a different fsid lower down, I xor the result with the export-point fsid, the result would be fairly clean (the xor difference between the two subvol ids) and could be safely mixed into the fsid we currently report. So all I REALLY need from btrfs is a "mounted-on" inode number, matching what readdir() reports. I wouldn't argue AGAINST getting cleaner fsid information. A 128-bit uuid and a 64bit subvol id would be ideal. I'd rather see them as new STATX flags than a new export_operations callback. NeilBrown
