Ability to restrict diskspace per user

[Bernhard Keller]

for example restrict disk space to 500Mb per user

add user.used\_space =

check prior to upload if space is exceeded
on successful upload add image size to used\_space( check size
after possible resize/conversion )

Do we use the same restriction for every user, or should it be
possible to set a limit for every account ?
possible delete option ? ( what happens to comments )