false directory cycle because all zfs filesystems share the same device inode

[dajhorn]

All ZFS filesystems share the same device inode, which confuses programs that check for directory cycles by keeping a list of mount points. For example:

$ find /tank
find: File system loop detected; '/tank/teacup' is part of the same file system loop as '/tank'.

$ du -sh /tank
du: WARNING: Circular directory structure.
This almost certainly means that you have a corrupted file system.
NOTIFY YOUR SYSTEM MANAGER
The following directory is part of the cycle: '/tank/teacup'

These two examples are in the Linux coreutils package, in lib/fts-cycle.c file, in the enter_dir() function.

[behlendorf]

Set stat->st_dev and statfs->f_fsid

Filesystems like ZFS must use what the kernel calls an anonymous super
block. Basically, this is just a filesystem which is not backed by a
single block device. Normally this block device's dev_t is stored in
the super block. For anonymous super blocks a unique reserved dev_t
is assigned as part of get_sb().

This sb->s_dev must then be set in the returned stat structures as
stat->st_dev. This allows userspace utilities to easily detect the
boundries of a specific filesystem. Tools such as 'du' depend on this
for proper accounting.

Additionally, under OpenSolaris the statfs->f_fsid is set to the device
id. To preserve consistency with OpenSolaris we also set the fsid to
the device id. Other Linux filesystem (ext) set the fsid to a unique
value determined by the filesystems uuid. This value is unique but
maintains no relationship to the device id. This may be desirable
when exporting NFS filesystem because it minimizes to chance of a
client observing the same fsid from two different servers.

Closed by 53cf50e