[clue-tech] sendfile(2) doesn't work with unionfs.

[David L. Anselmi]

Jim Ockers wrote:
[...]
> (I almost asked you to write a brief note for the list about what it
> was but luckily google is very effective.)  Unionfs is very cool.  Can
> you think of some good reason why unionfs doesn't support sendfile()?
> Or have they just not gotten around to implementing it, do you suppose?

There are cases (on NFS and others) where using sendfile on unionfs will 
oops.  So I think they'll get there, they just haven't figured it out yet.

> Also are you using unionfs just to get your distribution installed or
> are you using it for something more interesting, like ....?

Well, all I'm doing now is merging the pool directories on 5 CDs into 
one pool directory.  That makes my 5 CDs look like a single directory, 
which is what the real mirrors look like.

Debian repositories are flexible enough though that I could use 
pool/[1-5] links to the 5 CDs.  Since I have to generate the Packages 
files with the paths in them anyway that would work fine.  A trade off 
between clean implementation and easy Apache config.

The really interesting thing is to mount something like a CD along with 
a writable device and then the CD files look writable (sort of a copy on 
write idea).  The live CD people are doing that but at the moment I 
don't have any use for it.  Collins could probably use it where he 
shares home directories between distros, to remove the mount point he 
uses under home/collins for his shared files.  Unless he prefers that it 
be explicit what is shared and what isn't.

Dave