[Unionfs] What branch is a file from?

[Erez Zadok]

Robin,

Yes, this functionality exists already, as an ioctl you can call from any C
program, or as a userlevel utility you can put in, say, shell scripts.  You
need to get the unionfs-utils package.  In it, there's a tool called
unioctl.  Here's an example of its use:

1. File 'a' comes from branch /n/lower/b1

$ ./unionctl /mnt/unionfs/a --query
/mnt/unionfs/a  /n/lower/b1 (r--)


2. File 'b' comes from branch /n/lower/b2

$ ./unionctl /mnt/unionfs/b --query
/mnt/unionfs/b  /n/lower/b2 (r--)


3. Directory 'D' comes from two branches: /n/lower/b0 and /n/lower/b2

$ ./unionctl /mnt/unionfs/D --query
/mnt/unionfs/D  /n/lower/b0 (rw-)
/mnt/unionfs/D  /n/lower/b2 (r--)

Cheers,
Erez.