wiki:FixingLiblocker

Version 1 (modified by broder, 12 years ago) (diff)

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Overview

With the introduction of PyHesiodFS, a lot of the traditional functionality of liblocker and programs that use it (attach, detach, add, quota, fsid, zinit) is no longer necessary, and in fact, actively detrimental to smooth locker interactions. We'd like to replace the C library and programs with a more maintainable Python package and Python scripts, also using this as an opportunity to prune outdated, unused, or unnecessarily complex functionality. In general, the responsibility of tracking state should fall to PyHesiodFS, while liblocker should only be responsible for those operations which can't be performed from the filesystem.

For example, liblocker currently uses an attachtab (stored in /var/run/attachtab on Debathena machines) to track which lockers have been attached by which users. Instead, liblocker should simply list the contents of /mit; since PyHesiodFS provides a view of /mit that is unique per-user, ls /mit will only show those filesystems which have been mounted by the current user.

On the other hand, attach has traditionally been responsible for subscribing the user to zephyr notifications for the fileserver of filesystems being mounted, or acquiring the credentials needed to access a filesystem. Because of OS-level privilege separations, it's not possible for PyHesiodFS to do either of these things, so they must still be handled by attach

Related Tickets

#227, #228, #202

attach.conf

Much of /etc/athena/attach.conf is currently being used to limit the set of directories on which attach will operate. Post-revision, liblocker and its utilities will only operation on first-level subdirectories of /mit, so this configuration is not necessary. Any necessary filesystem configuration (such as NFS mount options) will be handled by PyHesiodFS or off-loaded (e.g. to an autofs /net automounter).

/etc/athena/attach.conf is no longer needed.

attach

In its most basic form, attach in an automounted world simply consists of a call to stat(2). However, we also want to preserve more advanced usage of attach, so most of the current functionality of attach should be retained.

Explicit mountpoints/targets can be created using os.symlink (using os.rmdir may be necessary if the mountpoint already exists). These mountpoints no longer require root privileges to create.

Finally, the following options from the attach manpage should be dropped:

--master (-M), --mountoptions (-o), --nosetuid (-nosuid or -N), --setuid (-suid or -S), --override (-O`)

detach

As with attach, detach can mostly be expressed as a single syscall: unlink(2) (i.e. os.remove). Since all operations against PyHesiodFS only affect the current user, no operations require privilege.

The following options to detach can be dropped; all others should be preserved:

--override (-O), --clean (-C)