Walkthrough: per-version isolation

Prototype: Commands and output shown reflect the current prototype and may change.

Overview: Each installed version of a program has its own storage area. After an update, the new version cannot open files the old version created. Rolling back makes the old files available again — they were never copied into the new area.

See HJFS overview for why. This walkthrough is the CLI shape of that rule.

1. Check the installed program version

$ ./start_TinyDemo -V
TinyDemo v1.0

2. Write and read a data file under v1

The w flag writes text to a file; r reads it back. Both calls run as TinyDemo v1, so they share v1’s storage area.

$ ./start_TinyDemo w FileA
$ ./start_TinyDemo r FileA
The apple was a shiny red color.

3. Build and install a new version

$ ./make_TinyDemo-2.sh
$ ./HJFS_update_program TinyDemo TinyDemo TinyDemo.hash

List installed versions. The identifiers are install-time labels; HJFS enforces the hash.

$ ./HJFS_version_manager TinyDemo -l
260208_123022P  TinyDemo v1.0  (hash …)
260208_124510P  TinyDemo v2.0  (hash …)  [active]

4. v2 cannot read v1’s FileA

v2 is now active. FileA still exists in v1’s storage area. It is not in v2’s.

$ ./start_TinyDemo -V
TinyDemo v2.0
$ ./start_TinyDemo r FileA
FileA: not in this version's storage area

That miss is the isolation. A malicious update is a new hash, so it starts with an empty area and cannot open the prior version’s files. To give v2 a copy, use the file transfer utility — not open() from v2. See Secure file transfer.

5. Write FileA under v2

v2 can create its own FileA. That is a different file in a different area. v1’s copy is unchanged.

$ ./start_TinyDemo w FileA
$ ./start_TinyDemo r FileA
The pear was a dull green color.

6. Roll back to v1

Confirm the active version, then set it back to the first. Rollback does not copy or merge files. It makes v1’s area the one open() resolves.

$ ./HJFS_version_manager TinyDemo -c
260208_124510P  TinyDemo v2.0  [active]
$ ./HJFS_version_manager TinyDemo -s 260208_123022P
$ ./start_TinyDemo -V
TinyDemo v1.0
$ ./start_TinyDemo r FileA
The apple was a shiny red color.

v2’s pear is still in v2’s area. It is not gone; it is not visible while v1 is active. The file transfer utility can copy it across if you need it. See Version rollback.