Re: [Xen-devel] [GIT PULL] Xen updates for 3.17-rc0

[Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>]

On Wed, Aug 6, 2014 at 2:14 AM, David Vrabel <dvrabel@xxxxxxxxxx> wrote:
>
> Note there will be some minor conflicts because "x86/xen: safely map
> and unmap grant frames when in atomic context" was cherry-picked from
> this branch for 3.16.  It's not clear why git didn't do the right
> thing automatically.

The reason is that while both branches have the same patch, one of
them has additional changes on top of that patch that means that the
two branches do not agree on what the end result should be.

There are broken systems that think that "same patch" means that it
should be a common base that should be merged on top of (resulting in
the merge being the superset patch). That's BS, and git doesn't do
that, even if that's _often_ the right thing to do (but the patch on
top might have become irrelevant due to other patches in the other
tree). So Git only cares about "branch A resulted in X, branch B
resulted in Y, the two changed the same file differently".

Anyway, now you know. Cherrypicking is *not* the answer to "no merge
conflicts". Not if the two branches then disagree in other details wrt
the cherry-picked code, like in this case.

           Linus

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