Re: Unfortunate interaction between git diff-index and fakeroot

[Elazar Leibovich <elazar.leibovich@oracle.com>]

On 12/07/2017 05:31 PM, Junio C Hamano wrote:
> Correct.  fakeroot would report that the files that are actually
> owned by the user who is running fakeroot are owned by root; the
> cached stat information in the index would be "corrected" to say
> that they are owned by root.  So once the index is refreshed like
> so, things will become consistent.
I still fail to understand, what's the benefit of storing the owner ID in
the index, where no one seems to use this information.
I mean, one could store many other meta information in the index, such as
ACL lists,  number of blocks allocated, etc, but the code seems to
ignore unused information, such as commit 
2cb45e95438c113871fbbea5b4f629f9463034e7
which ignores st_dev, because it doesn't actually matter, or
commit e44794706eeb57f2ee38ed1604821aa38b8ad9d2 which ignores
mode changes not relevant to the owner.

In which situation does anyone care about the owner UID?
What's the difference between that, and, e.g., st_dev?
> If you are using "diff-index" for the "is the tree dirty?" check
> without running "update-index --refresh", then you are not using
> the command correctly.
Just want to clarify. It seems like the linux kernel is using diff-index
to do just that, in scripts/setlocalversion

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/scripts/setlocalversion#n77

Do I understand correctly that linux should update the index
first, or better, use porcelain "git diff --name-only" instead?

It seems to be the case previously, but in commit 
cdf2bc632ebc9ef512345fe8e6015edfd367e256
git update-index was removed, to prevent error messages on
read-only linux tree.

Do I understand correctly that the more correct solution
for modern git, is to use git diff --name-only instead? It should
work on read-only as well as on read-write trees, and
would not break if anyone uses git under fakeroot.

Did I understand you correctly?