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Date: Tue, 23 Jun 2009 14:09:19 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] [RFC PATCH 00/15] Be able to compile out not needed
	options
References: <cover.1245764569.git.quintela@redhat.com>
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To: quintela@redhat.com
Cc: qemu-devel@nongnu.org

quintela@redhat.com wrote:
> From: Juan Quintela <quintela@redhat.com>
>
> Hi
>
> this series of patches:
> a- move object files only used by one target to that target Makefile.target
> b- add flags to disable parts: --disable-{bluez,usb,vwmare,virtio,scsi}
>    defaults is leave it enabled.  You need to add the --disable-* flag to get any change
> c- disable the use of --smb <dir>
>
> What is the intent:  we want to be able to not compile-in things that we are not
> interested in (they are experimental/not needed for our target/...).
>
> Is this the right approach?  Should I do something different?
>
> For the next series, I am also interested on enable/disabling bits of a subsysem:
> being able to support usb-hid but not usb-{host,net,msnd}.  I already have patches
> to disable that, just waiting to hear what is the preffered way to get
> that functionality.
>
> Known problems:
> - qemu-*.hx files don't run over cpp and then we are not able to remove from
>   the help page the options that we don't support.
> - drive_hot_add without scsi support do nothing.
>
> Any comments?
>   

To me, there are a few fundamental requirements for this:

1) This be configurable via a .config file instead of via ./configure 
options.
2) This involve no additional #ifdefs in the code
3) In the Makefiles, instead of having ifdef conditionals, we do:
    objs-$(CONFIG_FOO) += foo.o

The block/ drivers are the model here.  If you drop individual files 
from the build, it Just Works.

Regards,

Anthony Liguori