Re: [PATCH] Move read_mostly definition to asm/cache.h

[Junio C Hamano <junkio@cox.net>]

Linus Torvalds <torvalds@osdl.org> writes:

>> I accidently committed this to an up-to-date master branch, as
>> I forgot to check out the temporary branch I was going to commit
>> it on. Swapping the sums from .git/refs/heads/{master,read_mostly}
>> wouldn't break anything, if the only different between the two was
>> this commit, right?
>
> Correct. The branch head files really are just plain ascii references to 
> the top commit, you can rename branches by just renaming the file (and 
> thus switch branches by just cross-renaming them, ie just switching the 
> contents).

Careful.

If one of the swapped branches is your current branch
(i.e. pointed at by .git/HEAD), you need to remember to
switch that as well.

For example, after making the mistake of committing to "master":

	$ git commit ;# oops, to the master
        $ git show-branch origin master read_mostly
	!   [origin] latest update from Linus
         *  [master] latest for read_mostly
          ! [read_mostly] last update from Linus
        ---
         +  [master] latest for read_mostly
        +++ [origin] last update from Linus

Then swap heads:

	$ read_mostly_head=`cat .git/refs/heads/master`
        $ cat .git/refs/heads/read_mostly >.git/refs/heads/read_mostly
	$ echo "$read_mostly_head" >.git/refs/heads/read_mostly

At this point:

        * Your index file still matches $read_mostly_head
	* Your working tree matches your index file
	* Your .git/HEAD is pointing at .git/refs/heads/master

Essentially, you are (you want to be) in read_mostly branch, but
your .git/HEAD incorrectly says you are on the master branch.
So you would need:

	$ git symbolic-ref HEAD refs/heads/read_mostly

after swapping.  Then you would be on read_mostly branch.

        $ git show-branch origin master read_mostly
	!   [origin] latest update from Linus
         !  [master] last update from Linus
          * [read_mostly] latest for read_mostly
        ---
          + [read_mostly] latest for read_mostly
        +++ [origin] last update from Linus

BTW, would people object if I made the show-branch output like
this?


        $ git show-branch origin master read_mostly
	!   [origin] latest update from Linus
         !  [master] last update from Linus
          * [read_mostly] latest for read_mostly
        ---
          * [read_mostly] latest for read_mostly
        ++* [origin] last update from Linus