[olpc-software] Package manager stuff

[David Zeuthen]

On Wed, 2006-03-15 at 20:07 +0000, Mike Hearn wrote:
> Union mounts are not totally essential. I proposed them because a _lot_
> of software assumes everything is installed under /usr, /etc and so on.

I wonder... what's wrong with a cheap-skate solution including a daemon
that just create / destroy symlinks in /usr when it sees files come and
go in /applications and /media/<mountpoint>/? Surely the daemon would
use inotify for this task. Perhaps this is what you meant with a FUSE
solution in an earlier mail? A FUSE file system would however create an
unwanted redirection to user space for every file opened.. not sure we
want that penalty.

Also.. we might even have /usr on tmpfs and create the mapping from the
OS supplied /usr and all apps in /applications on each boot? With a
little bit work you might even do this for Fedora without changing the
file system layout at all; it would all be possible from either the
initrd or maybe even later, e.g. just before we mount /usr. When unionfs
is ready for prime time we simply use that instead.

Question: what would the cost of having /usr with symlinks on tmpfs be?
Both space-wise (how much RAM would it take) and CPU-cycle wise (how
much time would it take to populate /usr)? IIRC tmpfs is rather smart
these days (don't use a full 4kb inode for every file); this happened
after certain distributions (including Fedora) started using it
for /dev.

    David