On 10/20/19 8:28 AM, Vegard Nossum wrote:

On 10/20/19 5:17 AM, Willy Tarreau wrote:
On Fri, Oct 18, 2019 at 03:14:56PM -0400, Theodore Y. Ts'o wrote:
On Fri, Oct 18, 2019 at 06:50:51PM +0200, Vegard Nossum wrote:
The problem I ran into with putting the metadata at the end was
detecting where the diff ends. A comment in 'git apply' suggested that
detecting the difference between "--" as a diff/signature separator and
as part of the diff is nontrivial in the sense that you need to actually
do some parsing and keep track of hunk sizes.

Could we cheat by having "git format-patch" add a "Diff-size" in the
header which gives the number of lines in the diff so git am can just
count lines to find the Trailer section?

Be careful with this, it starts like this and ends up with non-editable
patches. I'd rather have git-am use best-effort detection of the end.

Expect filesystem developers to come up with a format that uses extents ;-)

Also when dealing with stable backports, I've done a lot of
"cat foo.diff >> bar.patch" to fixup some patches in which I just had
to move some parts around. Having to count lines and edit a counter
somewhere is going to become really painful.

I almost have some new patches ready for putting the metadata after the
patch using a very bare-bones diff parser (it's actually not that bad),
I just need to fix a few corner cases that are causing breakage in the
git test suite.

I sent v2 of the patches (with metadata _after_ the diff) to the git
list here:


As I wrote in there, we could already today start using

  git am --message-id

when applying patches and this would provide something that a bot could
annotate with git notes pointing to lore/LKML/LWN/whatever. I think that
would already be a pretty nice improvement over today's situation.

Sadly, since the beginning of 2018, this was only used for a measly
~0.14% of all non-merge commits in the kernel:

$ git rev-list --count --no-merges --since='2018-01-01' --grep 'Message-Id: ' linus/master

$ git rev-list --count --no-merges --since='2018-01-01' linus/master

So how can we spread the word about --message-id and get maintainers to
actually use it? I don't suppose it's reasonable to change the 'git am'
default setting?


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