RFC: generic file operation for fstrim ioctl()

["Enrico Weigelt, metux IT consult" <info@metux.net>]

Hello friends,


here's an RFC for a generic implementation of the FITRIM ioctl:

* introduce a new file_operation call vector for fstrim
* move the generic pieces (eg. cap check, copy from/to userland, etc)
  into a generic implementation that then calls into the fileop
* passing to the old ioctl fileop when fstrim op is NULL
* convert a few fs'es to the new schema

Rationale: it seems that all file systems implement generic stuff like
permission checks and buffer copy from/to userspace, all on their own.
We already have a common place for generic ioctl() handling (do_vfs_ioctl).
I feel its time for factoring this out the common fstrim pieces, too.

The first patch of this series introduces a new file_operation and calls
it on FITRIM (from do_vfs_ioctl) if it's set - otherwise just passes
the ioctl to file_ioctl(), as it had been before. So, this only becomes
active on a fs thats converted to the new file_operation. Subsequent patches
do the conversion for a few file systems.

Note this is just an RFC, don't apply it - there might still be bugs in there.


have fun,

--mtx