UID mapping filesystem

Phillip Susi psusi at cfl.rr.com
Wed May 12 01:24:15 UTC 2010

I don't see what FUSE would have to do with anything.  The UDF
filesystem has the ability to not store the uid on the media, instead
writing a uid of -1, which it then can map to the currently logged in
interactive user that mounted the disc later.  This feature was created
specifically to solve this sort of problem.  Adding that kind of ability
to ext4 should solve the problem for that fs as well, and would not be
very difficult either.  I wrote some patches a few years ago to flesh
out this capability in UDF, adding the ability to specify whether a uid
that is stored on the disk should be ignored and treated like it is -1
anyhow.  Unfortunately UDF has not seen the kind of widespread adoption
for use on removable media I had hoped for.  It is worth noting that
Microsoft Windows refused to mount UDF on non optical media, otherwise
it would make a good fs for a shared hard disk partition for those who
dual boot, having the ability to retain permissions unlike fat and ntfs,
but still being recognized by Windows.  Widespread support for packet
written mountable UDF filesystems on rewritable optical media also has
not materialized.  That has been on my to-do list for a few years now.

On Tue, 2010-05-11 at 18:03 +0000, Tiago Espinha wrote:
> Dear all,
> I'm a postgraduate student at the University of Leicester and the time
>  has come for me to do my thesis. This thesis can be in the format of a
>  technical project and one of the topics that has been proposed for my
>  course has to do with Linux.
> More concretely, the idea is that the student develops a FUSE file
>  system that maps that user's user ID across several terminals. The
>  purpose of this would be that if I have a USB stick formatted with
>  ext4 and I copy files to it at my Linux terminal at home, I would be
>  able to access these files from my terminal at work.
> As it is, according to this project's description (I'm no guru on this
>  matter), when we attempt to do what I've described, we won't have
>  permissions (unless the files are chmod'ed to 777) to read the files,
>  set aside modify them. Of course that as long as you are a super-user,
>  you can always chown them to your user in the local terminal and all
>  is well. However, you would have the same exact problem when returning
>  to your other terminal.
> My question is: does the community agree that this would be feasible
>  with a FUSE file system AND that is this an actual feature with appeal
>  and usefulness to the community? Has this been requested a lot or not
>  really?
> I have to make up my mind between this project and another one by
>  tomorrow so if anyone has an opinion or take on this, I'm all ears!
> Thanks in advance,
> Tiago

More information about the Ubuntu-devel-discuss mailing list