Re: [PATCH] x86: defconfig: Enable CONFIG_FHANDLE

[Richard Weinberger <richard@nod.at>]

Am 30.11.2014 um 21:54 schrieb Dave Chinner:
> On Wed, Nov 26, 2014 at 12:36:52AM +0100, Richard Weinberger wrote:
>> systemd has a hard dependency on CONFIG_FHANDLE.
>> If you run systemd with CONFIG_FHANDLE=n it will somehow
>> boot but fail to spawn a getty or other basic services.
>> As systemd is now used by most x86 distributions it
>> makes sense to enabled this by default and save kernel
>> hackers a lot of value debugging time.
> 
> The bigger question to me is this: why does systemd need to
> store/open by handle rather than just opening paths directly when
> needed? This interface is intended for stable, pathless access to
> inodes across unmount/mount contexts (e.g. userspace NFS servers,
> filesystem backup programs, etc) so I'm curious as to the problem
> systemd is solving using this interface. I just can't see the
> problem being solved here, and why path based security checks on
> every open() aren't necessary...

Digging inter systemd source shows that they are using name_to_handle_at()
to get the mount id of a given path.
The actual struct file_handle result is always ignored.

Thanks,
//richard