RFC: Junction Point/NT Symlink Support

[Hans Leidekker]

On Tue, 2019-03-26 at 15:41 +0100, Jacek Caban wrote:
> On 3/25/19 6:55 PM, Erich E. Hoover wrote:
> > So, I have some questions for the group:
> > 1) Does this approach seem reasonable in general?
> > 2) Should the information be stored in the access time (correct "ls"
> > behavior) or the modification time (correct "tar" behavior)?
> > 3) Is there anything else that I'm missing?
> 
> 
> I didn't look deep enough at those areas to comment on general idea, but 
> for an additional flag, you could also include a magic string in link 
> location itself, something like ".///.///actual_target". It would be 
> preserved by tar. A simple stat would not be enough to check the flag, 
> so I'm not sure how practical that would be.

That looks attractive. If you need to set the link type with a separate
operation creating a junction point is no longer atomic.

It may also allow you to keep using regular symlinks inside
prefixes, transparent to Windows applications.

An issue I see with renameat2(RENAME_EXCHANGE) is that it needs two
files, which shouldn't be visible to applications at the same time.