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From: Jeff Hostetler <>
To: "Ævar Arnfjörð Bjarmason" <>,
	"Jeff King" <>
Cc: Git Mailing List <>,
	Junio C Hamano <>,
	Jeff Hostetler <>
Subject: Re: [PATCH v4 2/4] fsck: force core.checksumindex=1
Date: Tue, 4 Apr 2017 09:13:33 -0400	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 4/4/2017 4:23 AM, Ævar Arnfjörð Bjarmason wrote:
> On Tue, Apr 4, 2017 at 4:29 AM, Jeff King <> wrote:
>> On Mon, Apr 03, 2017 at 10:31:03PM +0200, Ævar Arnfjörð Bjarmason wrote:
>>> On Mon, Apr 3, 2017 at 8:53 PM,  <> wrote:
>>>> Teach fsck to override core.checksumindex and always verify
>>>> the index checksum when reading the index.
>>> Sorry to only chime in about this at v4.
>>> I think this patch & the documentation you added for
>>> core.checksumindex in 1/4 would be much less confusing if you made
>>> this a on-by-default command-line option like e.g. "full".
>>> With this patch nothing amends the documentation to indicate that the
>>> core.checksumindex is magically overridden when fsck runs, I think
>>> something like this (needs amending to integrate) on top would make
>>> this clearer:
>> I think that is the wrong direction to reduce confusion. We don't need
>> more options to twiddle this flag, we need fewer. For instance, in your
>> proposed documentation:
>>> @@ -61,6 +61,11 @@ index file, all SHA-1 references in `refs`
>>> namespace, and all reflogs
>>>         object pools.  This is now default; you can turn it off
>>>         with --no-full.
>>> +--[no-]checksum-index:
>>> +       Validate the checksum at the end of the index file, on by
>>> +       default, locally overrides any "core.checksumIndex" setting
>>> +       unless negated. See linkgit:git-config[1].
>> That tells us _what_ it does, but I'm left scratching my head with
>> "why".
>> I don't think there is any reason you would want fsck not to compute
>> that checksum (just like there is no option to ask fsck not to check
>> pack sha1 trailers).
>> I would go so far as to say that the config option itself is unnecessary
>> in this iteration of the series. I only asked for it so that we could
>> test the verification code paths (both for correctness and performance).
>> But if fsck can exercise the code path, we can check correctness that
>> way. And for performance, it's probably enough to test two separate
>> builds (which Jeff has already done).
>> Junio also asked for the usual "add a config, and then later we'll flip
>> the default" procedure. But IMHO that isn't necessary here. Nobody
>> should ever care about this flag. It was largely useless to check it on
>> every read in the first place. And if you suspect there's corruption in
>> your repository, you should run "git fsck".
> The part that confused my & I found unintuitive is that there's a new
> core.WHATEVER config that'll get silently overridden by a specific
> command, git-fsck.
> Nothing else I can think of in core.* works like this, i.e. it's a
> namespace for "applies to all of git", core.editor, core.ignoreCase
> etc.

My "force_core_checksum_index" global override was a bit of a hack.
I looked at having fsck explicitly set the "core.checksumindex" config
value (which would write to the disk in the code paths I followed)
before it loaded the index, but if we ever find an invalid checksum,
read_cache() would call die() and fsck would not have a chance to set
it back in the user's config.  So I introduced the global override.

> Having git-fsck have a command-line option that's on by default as I
> suggested is one way to get out of that confusion. It makes it a
> special case of a CLI option overriding some config.

I looked at doing that, but thought it would be overkill since
no one is likely to care about turning it off -- or rather, fsck
should always do it whenever it reads the index.

> But yeah, another way to resolve this is to get rid of the config
> option altogether, or document in git-config.txt that
> core.checksumIndex is obeyed by everything except git-fsck.

If there's no objections then, I'll just remove the config
setting and keep the force_ global for fsck.


  parent reply	other threads:[~2017-04-04 13:13 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-03 18:53 [PATCH v4 0/4] read-cache: call verify_hdr() in a background thread git
2017-04-03 18:53 ` [PATCH v4 1/4] read-cache: core.checksumindex git
2017-04-03 18:53 ` [PATCH v4 2/4] fsck: force core.checksumindex=1 git
2017-04-03 20:31   ` Ævar Arnfjörð Bjarmason
2017-04-04  2:29     ` Jeff King
2017-04-04  8:23       ` Ævar Arnfjörð Bjarmason
2017-04-04  8:27         ` Jeff King
2017-04-04 13:13         ` Jeff Hostetler [this message]
2017-04-04 20:18           ` Jeff King
2017-04-03 18:53 ` [PATCH v4 3/4] t1450-fsck: test core.checksumindex git
2017-04-03 18:53 ` [PATCH v4 4/4] p0002-read-cache: " git

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