Hi Michal, On Tue, 03 Jul 2018 at 18:23:12 +0200, Michal Humpula wrote: > Entry in /proc/mounts for ZFS is different as it refers to the actual ZFS > filesystem not to the devices of the underlying zpool. Which, from my point > of > view, makes more sense. Do you see a way to export all the required > information in sysfs that would be acceptable by you? From top of my head, I > can think of something like `/sys/fs/zfs/$FS/devices` where $FS can be > something like `tank/my/fs`.
So $FS is what's found in /proc/mounts' first column? For block devices this value is not canonical (eg. /dev/mapper/xyz vs. /dev/dm-0 vs. /dev/disks/by-uuid/$UUID vs. /dev/block/$maj:$min, etc.), but there is a documented way to normalise it and get the corresponding sysfs directory·ies dev/block/$maj:$min. For “traditional” file systems it's enough to run `stat -L -c%t:%T` and convert the values to base 10; for btrfs (and I guess some other FS:es I'm not aware of) the list is under /sys/fs/$FSTYPE/$UUID/devices, where $UUID is canonical and can be obtained from /proc/mounts' first column using a generic (non FS-specific) command. Since ZFS doesn't expose a block device one would need another documented way to resolve /sys/fs/zfs/$FS. Hopefully ‘tank/my/fs’ is unique and can't be aliased to something else, can it? (Again for LVM, /dev/mapper/$vgname-$lvname, /dev/dm-$n, /dev/$vgname/$lvname denote the same device, and AFAIK whether /proc/mounts contains one or the other is not documented.) Do the slash characters in ‘tank/my/fs’ hint at a hierarchy, or is it a flat string? In the latter case it makes sense to encode the slashes as hex-sequences (\x2f), like udev does for names under /dev/disk/by-label. FWIW /proc/mounts encodes special characters such as tabs, linefeeds, and spaces using octal escapes. While it's our scripts' job and not ZFS's to decode these, if there is any mangling under /sys/fs/zfs then this should be documented. > I think few other upcoming filesystems will have similar problems, e.g. > bcachefs. So it'd be great do expose the sysfs directories in a similar way; thanks for bringing that up :-) -- Guilhem.
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