ADR 0328 supersedes ADR 0325: shared data is a library with one home, kept usable by
its group rather than by ACL entries. The engine now makes each library's group and
each module's user in its libraries' groups; keeps a library's root and requested
sub-paths in its group with group write and setgid on its home, making missing
sub-paths as the root is; waits for the operator's word before touching a root that
holds data, and on the take act walks it by descriptor (no link, same filesystem,
bounded and resumed, files with other names left); holds the containers of a library
whose disk or mount is not there; and puts the tool runner's account in the group.
The ACL keeping, mask repair and watch are gone; an access is again as before ADR 0325.
NFS and FUSE report a zero f_fsid, so another export or another FUSE mount at the
same point was named alike and kept without a warrant; xfs's f_fsid follows the
device number. A filesystem is now named by its UUID (its device matched in
/dev/disk/by-uuid), else a nonzero f_fsid, else mountinfo's source; one that cannot
be named is never kept or taken. Entries left on a filesystem not back within 30 days
are forgotten, said once, and the naming read is shared per mount.
An ext4 or xfs library mounted by UUID can come back from a reboot as another device
(/dev/sdb1 as /dev/sdc1); naming the filesystem by mountinfo's source read that as a
move, stripped the warranted library's entries and asked for a new Approve. A
filesystem is now named by statfs's f_fsid (from the UUID, or the ZFS dataset), its
type and its mount point. Entries left on the filesystem a folder is on now are
merged back or held, never walked away, and a TakenOn naming a mount point is not
taken.
A walk run while a dataset was unmounted wrote onto root's empty mount point, or
"dropped" entries from it and forgot the ones on the data; a folder kept while empty
below an unnamed mount was then swept whole once the disk mounted, with no warrant.
Every walk is now judged as an apply is, a changed mount judges the folder afresh, and
systemd .mount units and mounts seen are read for the first-sight rule. Widening a
mask caps the entries it limited, so the owning group gains nothing. The watch lets
go of removed folders, re-arms on lost notice, reads users under its lock and ends
with its context. A drop that cannot read an ACL is counted, a broken folder's words
carry no path, a grant's group that could not be left is tried again, and a folder's
stat is bounded.
A module's containers ran as whatever their image chose and shared folders were
made writable by putting accounts in the folder's group (ADR 0312), which ADR 0325
supersedes. The engine now makes each declared module identity as a system account
with the controller's numbers, runs a container declaring `identity` as it, and keeps
each placed shared folder usable through one POSIX ACL entry per user, set through
the kernel's xattrs on descriptors it opened itself. A folder holding data is kept
only after the operator's warrant (the take act); a missing folder is made where its
data lives and waits where its disk is not; root's data is never kept. A watch and a
bounded sweep put back what an app narrows. The group grant is removed, and what it
put an account in is taken back.
Reuses the descriptor walks, the create act, the missing-path wait and the warrant-
backed act message from the paused issue 567 branch.
jschoubben