encfs unmounting with open fd

[Mikkel]

On 04/11/2010 01:28 PM, David L wrote:
> I just started playing around with encfs and noticed
> some behaviour that surprised me... not sure if
> it's a bug or a bad design or if I have unreasonable
> expectations.  But if I mount a directory like this:
> 
> encfs ~/.crypt ~/crypt
> 
> Then start editing a file in ~/crypt... eg:
> 
> emacs ~/crypt/foo &
> 
> Then if I try to unmount the crypt directory, I'd
> expect it to complain that it can't unmount it
> because it is busy.  But it happily lets me unmount
> it.  If I continue editing the file and save it, it creates
> a new file in the empty mount point directory.
> 
> Another thing I noticed is that the little desktop
> icon that pops up when I mount the crypt directory
> has a right click menu to unmount, but it gives
> an error about it not being in fstab when I try
> to unmount it that way.
> 
> Are either or both of these bugs?
> 
> Thanks,
> 
From the encfs man page:

CAVEATS
   EncFS is not a true filesystem. It does not deal with any of the
   actual storage or maintenance of files. It simply translates
   requests (encrypting or decrypting as necessary) and passes the
   requests through to the underlying host filesystem. Therefor any
   limitations of the host filesystem will likely be inherited by
   EncFS (or possibly be further limited).

   One such limitation is filename length. If your underlying
   filesystem limits you to N characters in a filename, then
   EncFS will limit you to approximately 3*(N-2)/4. For example
   if the host filesystem limits to 256 characters, then EncFS will
   be limited to 190 character filenames. This is because encrypted
   filenames are always longer then plaintext filenames.

So, in the first case, the file man not be open, or the open file is
most likely in the ~/.crypt folder, and not in the encfs mounted on
~/crypt. Some editors will open the file, read it, and close it
again. It ten works with a temporary copy of the file. When you save
the file, the original file is renamed as a backup, and the
temporary file replaces it.

In the second case, I think it is a matter of the umount command not
knowing how to handle a fuse-mounted file system. Not so much a bug
as an added feature that needs to be implemented so that umount
knows to hand the unmount of encfs off to fusermount.

Just my WAG
Mikkel
-- 

  Do not meddle in the affairs of dragons,
for thou art crunchy and taste good with Ketchup!

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