On 2021-01-05 at 14:21:40, Ævar Arnfjörð Bjarmason wrote: > > On Sun, Jan 03 2021, brian m. carlson wrote: > > I think it makes sense to split up 1-4/5 here from 5/5 in this series > since they're really unrelated changes, although due to the changes in > 1-4 they'll conflict. Okay, I'll drop them. > In v1 I pointed out you needed to read some combination of the cover > letter & the patch to see what this was intended for (see [1]). I think > for v3 the commit itself should summarize the trade-offs & design > choices. I can do that. It's a very long commit message anyway, but if you think it would be better in the commit message, I can add it. > > For projects which wish to support this, introduce hashed forms into the > > mailmap. These forms, which start with "@sha256:" followed by a SHA-256 > > hash of the entry, can be used in place of the form used in the commit > > field. This form is intentionally designed to be unlikely to conflict > > with legitimate use cases. For example, this is not a valid email > > address according to RFC 5322. In the unlikely event that a user has > > put such a form into the actual commit as their name, we will accept it. > > We'll emit the commit author information as-is in that case under "git > show", or run the mapping and map it via mailmap? Anyway, it seems > there's a test for this. Probably better to just point to it. It will be handled correctly via the mailmap code, in which case we'll make a no-op transformation. If the user is not using the mailmap, then it will be handled trivially. > > While the form of the data is designed to accept multiple hash > > algorithms, we intentionally do not support SHA-1. There is little > > reason to support such a weak algorithm in new use cases and no > > backwards compatibility to consider. Moreover, SHA-256 is faster than > > the SHA1DC implementation we use, so this not only improves performance, > > but simplifies the current implementation somewhat as well. > > I agree with most of this aside from the "weak algorithm" part. That > seems like an irrelevant aside for this specific use of a hashing > algorithm, no? We could even use MD5 here, so SHA256-only is just > setting is up for not needing to deal with SHA1 forever in this one > place in some SHA256 future repo. One should avoid the use of weak algorithms when possible even if they are not being used in a way that makes them weak because it incentivizes others to use them, often in a way that is insecure. I had a conversation with a junior candidate during an interview who said they used SHA-1 in a particular case "because Git uses it." That's why I mentioned it. > > Note that it is, of course, possible to perform a lookup on all commit > > objects to determine the actual entry which matches the hashed form of > > the data. However, this is an improvement over the status quo. > > > > The performance of this patch with no hashed entries is very similar to > > the performance without this patch. Considering a git log command to > > look up author and committer information on 981,680 commits in the Linux > > kernel history, either with an unhashed mailmap or a mailmap with all > > old values hashed: > > > > Shortest Longest Average Change > > Git 2.30 7.876 8.297 8.143 > > This patch, unhashed 7.923 8.484 8.237 + 1.15% > > This patch, hashed 14.510 14.783 14.672 +80.17% > > This patch, hashed, unoptimized 15.425 16.318 15.901 +95.27% > > > > Thus, the average performance after this patch is within normal > > variation of the pre-patch performance. It's unlikely that users will > > notice the difference in practice, even on much larger > > repositories, unless they're using the new feature. > > Am I reading this right that if there's a single hashed entry in > .mailmap anything using %aE or %aN is around 2x as slow? No, that's not the case. As soon as we see every hashed entry, we will stop hashing new entries. Linux is not necessarily the best case for this because it has a long history with many one-off contributors long ago in the history. I'll explain that further in the commit message and add some more metrics. > Your v1 mentioned that a project might "insert entries for many > contributors in order to make discovery of "interesting" entries > significantly less convenient." which is gone in the v2 patch. As noted > in [1] I don't see how it helps the obscurity much, but if that's still > the intended use we'd expect to get more slowdowns in the wild if users > intend to convert their whole mailmap to this form if they want a single > entry to use the form. Peff objected to that text, so I removed it. As mentioned above, it depends on who you put in the mailmap. If they're the most recent 50 contributors, it'll probably be pretty cheap. If you put the oldest contributors in there and they've not sent any recent commits, it will be more expensive. > Anyway, as you might have guessed I'm still not a fan of this direction. I've got that impression pretty strongly. I do want to point out that generally I'm pretty willing to change approaches and do things differently. I've completely redone a decent number of patches in the past in response to feedback on the list. I'm not changing the approach here because, as mentioned below, I don't think that just encoding meets the use cases I'm targeting here. So I have heard your suggestions and to be clear, I do value your input on this (and on other topics), it's just that I disagree that such a change is one I should make. > So the new->name/email mapping (as opposed to new->email) is really only > needed for some really obscure cases where two people shared an E-Mail > or something. That's unlikely, but it does happen. That's why we have it. > So we're talking about hiding the old E-Mail, presumably because it was > joe@ intsead of jane@, so in that case we could just support URI > encoding: > > Jane Doe <jane@xxxxxxxxxxx> > <jane@xxxxxxxxxxx> <%6A%6F%65@%64%65%76%65%6C%6F%70%65%72.%63%6F%6D> > > Made via: > > $ perl -MURI::Escape=uri_escape -wE 'say uri_escape q[joe@xxxxxxxxxxxxx], "^@."' > %6A%6F%65@%64%65%76%65%6C%6F%70%65%72.%63%6F%6D > > Which also has the nice attribute that people can make it obvious what > part they want to hide, since this is really a feature to enable social > politeness & consideration: > > Jane Doe <jane@xxxxxxxxxxx> > # I don't want to be known by my old name, thanks > <jane@xxxxxxxxxxx> <%6A%6F%65@xxxxxxxxxxxxx> I don't think this feature is going to get used if we just encode names or email addresses. In the United States, when someone transitions, they get a court order to change their name. I don't think a lot of corporate environments are going to want to just encode an old name or email address in a trivially invertible way given that. This is typically a topic handled with some sensitivity in most companies. I will tell you that I would not just use an encoded version if I were changing my name for any of the reasons I've mentioned. That wouldn't cut it for me, and I wouldn't use such a feature. The feature I'm implementing is a feature I've talked with trans folks about, and that's why I'm implementing this as it is. The response I got was essentially, "It's not everything I want, but it's an improvement." If the decision is that we want to go with encoding instead of hashing, then I'll drop this patch. I'm not going to put my name or sign-off on that because I don't think it meets the need I'm addressing here. The entire problem, of course, is that we bake a human's personal name and email address immutably into a Merkle tree. We know full well that people do change their names and email addresses all the time (e.g., marriage, job changes), and yet we have this design. In retrospect, we should have done something different, but hindsight is 20/20 and I'm just trying to do the best we can with what we've got. > 2. Hiding from your enemies > > For the other use-case of "abusive family or partner" I had the comment > in v1 of "but not so much that you'd still take the risk of submitting a > patch to .mailmap?". No, my use case isn't "hiding from an abusive family or partner". It's "I'm finally free of that **** and I never want to hear their name again." (I've known people in this situation.) Also, the similar use case of, "my family member, with whom I share an uncommon name, murdered someone, which I obviously found abhorrent, and I would like to not be associated with them when my name is Googled." And yes, I knew an acquaintance many years ago whose family member murdered someone. In other words, the person changed their name to disassociate themselves, not to hide from their abuser. > 4. Spam > > You mentioned this in your [2] (but not as a use-case in the v2 > re-rolled commit message): > > And we know that spammers and recruiters (which, in this case, are > also spammers) do indeed scrape repositories via the repository web > interfaces. > > Surely these people are most interested in the current E-Mail addresses, > which if they're scraping the common web interfaces (e.g. Github, > GitLab) are easily accessible there. It doesn't seem very plausible that > someone would care enough to scrape .mailmap for old addresses but not > just update their scraper to clone & run "git log" for the purposes of > e.g. their recruitment E-Mails. Unless the user is using the GitHub-provided noreply address or a similar address, which is common. This allows people to map all of their old addresses to such an address, which, judging from StackOverflow, is a thing people want to do. I can tell you from dealing with abuse that raising the bar even the tiniest bit is very significant to stopping it. Most recruiters are not developers and they and spammers don't have Git installed. They're going to rely on Googling or other public search functionality, and this makes that harder. Greylisting is exactly raising the bar the tiniest amount and it's extraordinarily effective. > 5. Interaction with other systems > > Something I mentioned in the last 3 paragraphs of my [1]. I think you're > only considering the cases where git itself does the mailmap > translation, but we have 3rd party systems that make use of the format > in good ways (also doing the Joe->Jane mapping). Making it a hassle for > those systems makes it more likely that Jane doesn't get the mapping she > wants. This is an argument for never changing the format. Sometimes things change, and I don't want to avoid making a change because other implementations haven't implemented it yet. Under that approach, we'd never have the SHA-256 work. -- brian m. carlson (he/him or they/them) Houston, Texas, US
Attachment:
signature.asc
Description: PGP signature
