Re: [Qemu-devel] [PATCH v7 00/11] Add basic "detach" support for dump-guest-memory

[Markus Armbruster <armbru@redhat.com>]

Peter Xu <peterx@redhat.com> writes:

> Changes from v7:
> - patch 8: use s->dump_info.page_size not TARGET_PAGE_SIZE
> - patch 10: change DUMP_STATUS_MAX to DUMP_STATUS__MAX (this is to
>   fix compile error for rebasing to latest master branch, still do
>   not know why we need this change from generating "_MAX" to
>   "__MAX" for enum types...)

Don't ask yourself why something was done, ask git :)

    $ git-log -S__MAX
    [...]
    commit 7fb1cf1606c78c9d5b538f29176fd5a101726a9d
    Author: Eric Blake <eblake@redhat.com>
    Date:   Wed Nov 18 01:52:57 2015 -0700

--->    qapi: Don't let implicit enum MAX member collide

        Now that we guarantee the user doesn't have any enum values
        beginning with a single underscore, we can use that for our
        own purposes.  Renaming ENUM_MAX to ENUM__MAX makes it obvious
        that the sentinel is generated.

        This patch was mostly generated by applying a temporary patch:

        |diff --git a/scripts/qapi.py b/scripts/qapi.py
        |index e6d014b..b862ec9 100644
        |--- a/scripts/qapi.py
        |+++ b/scripts/qapi.py
        |@@ -1570,6 +1570,7 @@ const char *const %(c_name)s_lookup[] = {
        |     max_index = c_enum_const(name, 'MAX', prefix)
        |     ret += mcgen('''
        |     [%(max_index)s] = NULL,
        |+// %(max_index)s
        | };
        | ''',
        |                max_index=max_index)

        then running:

        $ cat qapi-{types,event}.c tests/test-qapi-types.c |
            sed -n 's,^// \(.*\)MAX,s|\1MAX|\1_MAX|g,p' > list
        $ git grep -l _MAX | xargs sed -i -f list

        The only things not generated are the changes in scripts/qapi.py.

        Rejecting enum members named 'MAX' is now useless, and will be dropped
        in the next patch.

        Signed-off-by: Eric Blake <eblake@redhat.com>
        Message-Id: <1447836791-369-23-git-send-email-eblake@redhat.com>
        Reviewed-by: Juan Quintela <quintela@redhat.com>
        [Rebased to current master, commit message tweaked]
        Signed-off-by: Markus Armbruster <armbru@redhat.com>

I guess this isn't perfectly clear without more context, so let me add
some.

The implicit FOO_MAX could collide with the user's FOO_MAX for QAPI
enumeration values 'max', or case variations thereof.  Commit cf39359
added extra code to catch that.

Renaming the implict FOO_MAX to FOO__MAX removes the need for the
special rule "you can't use 'max' as an enumeration value", because the
general rule "names starting with '_' are reserved" suffices then.

Fewer rules is better.

[...]