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Re: [Qemu-devel] [PATCH v2 22/29] qapi: Generate separate .h, .c for eac

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH v2 22/29] qapi: Generate separate .h, .c for each module
Date: Mon, 12 Feb 2018 16:06:28 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0

On 02/11/2018 03:36 AM, Markus Armbruster wrote:
Our qapi-schema.json is composed of modules connected by include
directives, but the generated code is monolithic all the same: one
qapi-types.h with all the types, one qapi-visit.h with all the
visitors, and so forth.  These monolithic headers get included all
over the place.  In my "build everything" tree, adding a QAPI type
recompiles about 4800 out of 5100 objects.

We wouldn't write such monolithic headers by hand.  It stands to
reason that we shouldn't generate them, either.

Split up generated qapi-types.h to mirror the schema's modular
structure: one header per module.  Name the main module's header
qapi-types.h, and sub-module D/B.json's header D/qapi-types-B.h.

Mirror the schema's includes in the headers, so that qapi-types.h gets
you everything exactly as before.  If you need less, you can include
one or more of the sub-module headers.  To be exploited shortly.

Split up qapi-types.c, qapi-visit.h, qapi-visit.c, qmp-commands.h,
qmp-commands.c, qapi-event.h, qapi-event.c the same way.
qmp-introspect.h, qmp-introspect.c and qapi.texi remain monolithic.

Make sense.

The split of qmp-commands.c duplicates static helper function
qmp_marshal_output_str() in qapi-commands-char.c and
qapi-commands-misc.c.  This happens when commands returning the same
type occur in multiple modules.  Not worth avoiding.

As long as it is static, and neither .c file includes the other, we're fine (gdb may have a harder time figuring out which copy to put a breakpoint on, but that's not too terrible).

Since I'm going to rename qapi-event.[ch] to qapi-events.[ch], and
qmp-commands.[ch] to qapi-commands.[ch], name the shards that way
already, to reduce churn.  This requires temporary hacks in
commands.py and events.py.  They'll go away with the rename.

The planned rename makes sense; prepping now is fine.

Signed-off-by: Markus Armbruster <address@hidden>
  .gitignore               |  60 ++++++++++++++++++++++++
  Makefile                 | 120 +++++++++++++++++++++++++++++++++++++++++++++++
  Makefile.objs            |  65 ++++++++++++++++++++++++-
  scripts/qapi/commands.py |  35 +++++++++-----
  scripts/qapi/common.py   |  21 +++++++--
  scripts/qapi/events.py   |  19 ++++++--
  6 files changed, 300 insertions(+), 20 deletions(-)

diff --git a/.gitignore b/.gitignore
index 9477a08b6b..42c57998fd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -31,7 +31,67 @@

Is it worth using a glob instead of specific patterns, as in:


Maybe being precise doesn't hurt, if we aren't adding sub-modules all that often; but being generous with a glob makes it less likely that a future module addition will forget to update .gitignore.

+++ b/Makefile
@@ -92,10 +92,70 @@ include $(SRC_PATH)/rules.mak
  GENERATED_FILES = qemu-version.h config-host.h qemu-options.def
  GENERATED_FILES += qapi-builtin-types.h qapi-builtin-types.c
  GENERATED_FILES += qapi-types.h qapi-types.c
+GENERATED_FILES += qapi/qapi-types-block-core.h qapi/qapi-types-block-core.c

For the makefile, I'd suggest using an intermediate list of module names, and then using make string operations to expand it into larger lists, to cut down on the repetition. Something like (untested):

QAPI_MODULES = block-core block char common ...
GENERATED_FILES += $(addprefix qapi/qapi-types-,$(addsuffix .c,$(QAPI_MODULES)) GENERATED_FILES += $(addprefix qapi/qapi-types-,$(addsuffix .h,$(QAPI_MODULES))

@@ -525,10 +585,70 @@ qapi-modules = $(SRC_PATH)/qapi-schema.json 
$(SRC_PATH)/qapi/common.json \
qapi-builtin-types.c qapi-builtin-types.h \
  qapi-types.c qapi-types.h \
+qapi/qapi-types-block-core.c qapi/qapi-types-block-core.h \
+qapi/qapi-types-block.c qapi/qapi-types-block.h \

And repeating the list of filenames; again, an intermediate variable would let you do:



  qmp-introspect.h qmp-introspect.c \
  qapi-doc.texi: \
  qapi-gen-timestamp ;

Not only does it cut down on the repetition, but it will make adding a future module easier.

diff --git a/Makefile.objs b/Makefile.objs
index 2813e984fd..7a55d45669 100644
--- a/Makefile.objs
+++ b/Makefile.objs
@@ -3,8 +3,56 @@
  stub-obj-y = stubs/ crypto/
  util-obj-y = util/ qobject/ qapi/
  util-obj-y += qapi-builtin-types.o
+util-obj-y += qapi-types.o
+util-obj-y += qapi/qapi-types-block-core.o

Perhaps this can also exploit make text manipulation?

Otherwise looks good.

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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