Re: [PATCH] checkout: most of the time we have good leading directories

[Thomas Rast <tr@thomasrast.ch>]

Junio C Hamano <gitster@pobox.com> writes:

> When "git checkout" wants to create a path, e.g. a/b/c/d/e, after
> seeing if the entire thing already exists (in which case we check if
> that is up-to-date and do not bother to check it out, or we unlink
> and recreate it), we validate that the leading directory path is
> without funny symlinks by seeing a/, a/b/, a/b/c/ and then a/b/c/d/
> are all without funny symlinks, by calling has_dirs_only_path() in
> this order.
>
> When we are checking out many files (imagine: initial checkout),
> however, it is likely that an earlier checkout would have already
> made sure that the leading directory a/b/c/d/ is in good order; by
> first checking the whole path a/b/c/d/ first, we can often bypass
> calls to has_dirs_only_path() for leading part.

Naively one would think that this is just as much work -- to correctly
verify that the path consist only of actual directories (not symlinks)
we have to lstat() every component regardless.  It seems the reason this
is an optimization is that has_dirs_only_path() caches its results, so
that we can get 'a/b/c/d/ is okay in every component' from the cache.

Is this analysis correct?  If so, can you spell that out in the commit
message?

-- 
Thomas Rast
tr@thomasrast.ch