Re: merged-/usr-via-symlinks vs a-different-layout
Guillem Jover writes:
> On Tue, 2019-02-19 at 08:54:12 +0100, Ansgar wrote:
>> Guillem Jover writes:
>> > 3) Switching packages to the merged-/usr layout could have been
>> > accomplished automatically via debhelper for a coverage of around
>> > 99% (?) of the archive. With something along the lines of:
>> >
>> > ,---
>> > D=debian/tmp
>> > for d in /bin /sbin /lib; do
>> > for p in $(find $D/$d ! -type d); do
>> > b="${p##$D/}"
>> > m="$D/usr$b"
>> > if [ ! -e "$m" ]; then
>> > mkdir -p "$(dirname $m)"
>> > mv "$p" "$m"
>> > ln -s "${m##$D}" "$p"
>> > fi
>> > done
>> > done
>> > `---
>> >
>> > With the property that it would handle gracefully all cases were the
>> > maintainer has checked that no compat symlinks are required and has
>> > then progressively moved the pathname installation to their final
>> > destination under /usr.
>>
>> That is not merged-/usr, but a different filesystem layout.
>>
>> So, no, it is not possible to switch packages to merged-/usr this way.
>
> You are still conflating the concept with the deployment. The
> underlaying properties of merging /usr is that the contents for
> directories that are present in both / and /usr get merged into
> /usr.
No, I'm saying that you are proposing yet another different file system
layout. Which is quite simple to see: the file system would differ.
You just claim it follows similar "ideas" in some way.
I can come up with other variations that move files to /usr too: have
/bin a symlink to /usr/root/bin (some for other directories). That
would also be a different file system layout which shouldn't be called
"merged-/usr" either.
(That would have no filesystem aliasing between /bin and /usr/bin;
policy has special rules to allow replacing top-level directories with
symlinks; but besides that it is different for no good reason so I don't
think it would be a good idea.)
> See for example OpenSUSE which did this transition correctly:
>
> <https://en.opensuse.org/openSUSE:Usr_merge>
"The special comments #UsrMerge, #EndUsrMerge will help us to clean up
the spec files once everything has been moved and we can create a
general link from /bin to /usr/bin for example. "
So they want a /bin -> /usr/bin symlink (and the same for the other
directories) just as in the proposal you call broken...
Maybe you have misunderstood what SuSE plans to do?
Having dpkg track a symlink /bin/${something} and a file
/usr/bin/${something} will break should /bin be turned into a symlink
happen. So there is no nice way to finish the transition. I'm not sure
how that would work on RPM; maybe SuSE got stuck with that? That would
be another good reason to not follow that way...
I wouldn't be surprised if that took about as long as the /usr/doc ->
/usr/share/doc transition. (If the change process for most simple
changes like file locations takes 10+ years then I say the process is
broken...)
Ansgar
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