Re: USE_SHA1DC is broken in pu

From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Mar 23, 2017, 17:16 UTC
Message-ID: <CA+55aFyFS2r6isdQU_i5FUQnrzjvWhZdmEVE=KmBVTrMukBbkw@mail.gmail.com>
In-Reply-To: <alpine.DEB.2.20.1703231724350.3767@virtualbox>

On Thu, Mar 23, 2017 at 9:43 AM, Johannes Schindelin <Johannes.Schindelin@gmx.de> wrote:

>
> What I am saying is that this should be a more fine-grained, runtime knob.

No it really shouldn't.

> If I write out an index, I should not suffer the slowdown from detecting
> collisions.

The index case is a complete red herring.

As already noted, the proper fix for the index case is to simply do it asynchronously on read. On write, it's harder to do asynchronously, but for a 300MB index file you're likely going to be doing IO in the middle, so it's probably not even noticeable.

But even *if* you want to worry about the index file, it shouldn't be a runtime knob. The index file is completely different from the other uses of SHA1DC.

But the fact is, if you don't want SHA1DC, and you have crazy special cases, you just continue to build with openssl support instead. Nobody else should ever have to worry about *your* crazy cases.

                Linus