[systemd-devel] name_to_handle_at() with UBIFS

[Lennart Poettering]

On Wed, 17.12.14 20:48, Umut Tezduyar Lindskog (umut at tezduyar.com) wrote:

> On Wed, Dec 17, 2014 at 7:54 PM, Lennart Poettering
> <lennart at poettering.net> wrote:
> > On Wed, 17.12.14 10:45, Umut Tezduyar Lindskog (umut at tezduyar.com) wrote:
> >
> >> For the record:
> >>
> >> It is not enough to have CONFIG_FHANDLE to get the support for
> >> name_to_handle_with(). The FS also needs to support it and UBIFS
> >> doesn't have support for it at the moment.
> >
> > For what precisely? The mount point detection code will actually fall back
> > to classic fstat() checks if name_to_handle_at() is not available on
> > both the mount point and its parent. Usually, this should be good
> > enough for most cases.
> >
> > Lennart
> 
> udev is also using name_to_handle_at() without fallback. And thats ok
> since we have the CONFIG_FHANDLE as requirement in our README file.
> But what I am saying is, it is not enough to have CONFIG_FHANDLE to
> make name_to_handle_at work. FS also needs to support it too.
> Unfortunately UBI doesn't have the support yet but it is more common
> to find the support on different FSs.

udev only uses name_to_handle_at() on /dev, which must be a devtmpfs
on systemd systems, and devtmpfs (by being a normal tmpfs in most
ways) supports name_to_handle_at() just fine.

Hence: name_to_handle_at() must be on in the kernel, but it's pretty
much OK if some other fs does not support it.

Lennart

-- 
Lennart Poettering, Red Hat