Re: [PATCH 01/02/RFC] implement a stat cache

From: Junio C Hamano <gitster@pobox.com>
Date: Apr 21, 2008, 20:06 UTC
Message-ID: <7vprsj9dmc.fsf@gitster.siamese.dyndns.org>
In-Reply-To: <alpine.LFD.1.10.0804211203460.2779@woody.linux-foundation.org>

Linus Torvalds <torvalds@linux-foundation.org> writes:

Show 31 quoted lines

> On Mon, 21 Apr 2008, Junio C Hamano wrote:
>> 
>> Doesn't it become very tempting to replace lstat() calls we make to check
>> the status of a work tree path, with a function git_wtstat() that is:
>
> Yes.
>
> That looks like a very good abstraction.
>
>>                 /*
>>                  * As far as git is concerned, this does not exist in
>>                  * the work tree!
>>                  */
>>                 errno = ENOENT;
>>                 return -1;
>>         }
>
> Well, how about returning something else than "ENOENT" here? 
>
> As you point out, git doesn't actually think this is a "does not exist" 
> case, but something else that may require more work:
>
>> This unfortunately is not enough to hide the need for has_symlink calls
>> from outside callers.  When we check out a new path "a/b/c/d/e", for
>> example, if we naively checked if we creat(2) "a/b/c/d/e" (and otherwise
>> we try the equivalent of "mkdir -p"), we would be tricked by a symlink
>> "a/b" that points at some random place that has "c/d" subdirectory in it,
>> and we need to unlink "a/b" first, and the above git_wtstat() does not
>> really help such codepath.
>
> Maybe ENOTDIR would be a better error return?

Yeah, and we could return which component in the given path is the offending one at the same time.

In the above example, we would say "No, a/b/c/d/e does not exist because a/b is a symlink". But would that be enough, I have to wonder. lstat(2) may have already said "There is no a/b/c/d/f" in the same example, but we still need to know "a/b" is an unwanted symbolic link if the reason we are asking that question is because we would want to check out "a/b/c/d/f".

So the answer need to be "a/b/c/d/f" (does not exist|exists in the work tree), and it cannot exist because "a/b" is a symlink for such a caller.

But when we are trying to git-add, we simply do not care such distinction.