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Re: [Qemu-block] [Qemu-devel] [PATCH] block: Make more block drivers com


From: Max Reitz
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH] block: Make more block drivers compile-time configurable
Date: Tue, 6 Nov 2018 01:54:00 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1

On 05.11.18 16:25, Markus Armbruster wrote:
> Max Reitz <address@hidden> writes:
> 
>> On 19.10.18 13:34, Markus Armbruster wrote:
>>> From: Jeff Cody <address@hidden>
>>>
>>> This adds configure options to control the following block drivers:
>>>
>>> * Bochs
>>> * Cloop
>>> * Dmg
>>> * Qcow (V1)
>>> * Vdi
>>> * Vvfat
>>> * qed
>>> * parallels
>>> * sheepdog
>>>
>>> Each of these defaults to being enabled.
>>>
>>> Signed-off-by: Jeff Cody <address@hidden>
>>> Signed-off-by: Markus Armbruster <address@hidden>
>>> ---
>>>
>>> Hmm, we got quite a few --enable-BLOCK-DRIVER now.  Perhaps a single
>>> list-valued option similar --target-list would be better.  Could be
>>> done on top.
>>>
>>>  block/Makefile.objs | 22 ++++++++---
>>>  configure           | 91 +++++++++++++++++++++++++++++++++++++++++++++
>>>  2 files changed, 107 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/block/Makefile.objs b/block/Makefile.objs
>>> index c8337bf186..1cad9fc4f1 100644
>>> --- a/block/Makefile.objs
>>> +++ b/block/Makefile.objs
>    @@ -1,10 +1,18 @@
>    -block-obj-y += raw-format.o qcow.o vdi.o vmdk.o cloop.o bochs.o vpc.o 
> vvfat.o dmg.o
>    +block-obj-y += raw-format.o vmdk.o vpc.o
>    +block-obj-$(CONFIG_QCOW1) += qcow.o
>    +block-obj-$(CONFIG_VDI) += vdi.o
>    +block-obj-$(CONFIG_CLOOP) += cloop.o
>    +block-obj-$(CONFIG_BOCHS) += bochs.o
>    +block-obj-$(CONFIG_VVFAT) += vvfat.o
>    +block-obj-$(CONFIG_DMG) += dmg.o
>    +
>     block-obj-y += qcow2.o qcow2-refcount.o qcow2-cluster.o qcow2-snapshot.o 
> qcow2-cache.o qcow2-bitmap.o
>>
>> [...]
>>
>>> @@ -45,7 +54,8 @@ gluster.o-libs     := $(GLUSTERFS_LIBS)
>>>  vxhs.o-libs        := $(VXHS_LIBS)
>>>  ssh.o-cflags       := $(LIBSSH2_CFLAGS)
>>>  ssh.o-libs         := $(LIBSSH2_LIBS)
>>> -block-obj-$(if $(CONFIG_BZIP2),m,n) += dmg-bz2.o
>>> +block-obj-dmg-bz2$(if $(CONFIG_BZIP2),m,n) += dmg-bz2.o
>>> +block-obj-$(CONFIG_DMG) += $(block-obj-dmg-bz2-y)
>>
>> This defines "block-obj-dmg-bz2m" or "block-obj-dmg-bz2n", so
>> "block-obj-dmg-bz2-y" is never defined (note both the missing hyphen and
>> the "m" vs. "y").
>>
>> How about:
>>
>> block-obj-dmg-bz2-$(CONFIG_BZIP2) += dmg-bz2.o
> 
> As far as I can tell, CONFIG_BZIP2 is either undefined or "y".  Thus,
> block-obj-dmg-bz2-y is either left undefined or set to dmg-bz2.o.

Yes.

> Perhaps the '+=' be ':=', but we seem to use '+=' pretty
> indiscriminately.

Yep.  I don't know.  Whatever works, and both do, so...

>> block-obj-$(if $(CONFIG_DMG),m,n) += $(block-obj-dmg-bz2-y)
> 
> As far as I can tell, CONFIG_DMG is also either undefined or "y".  So,
> this adds dmg-bz2.o to block-obj-m if both CONFIG_BZIP2 and CONFIG_DMG
> are enabled.

Yes.

> Shouldn't it be added to block-obj-y, like dmg.o, or am I confused?

The behavior before this patch was to add it to block-obj-m.
27685a8dd08c051fa6d641fe46106fc0dfa51073 has the explanation: We want
the bz2 part to be a module so you can launch qemu even without libbz2
around.  Only when you use dmg will it load that module.

(And if you dig deeper, it was 88d88798b7efe that (intentionally) broke
 that intended behavior, until it was restored by the above commit.)

>> Bonus point: The "+=" are naturally aligned!
> 
> Woot!

:-)

Max

>> (Fun fact on the side: I tried downloading some dmg image, but qemu
>> refused to open that.  ("sector count 409600 for chunk 4 is larger than
>> max (131072)" -- yeah, yeah, I know that I'm not the largest guy) -- but
>> you can test it just by replacing "dmg-bz2.o" by "does-not-exist.o", and
>> then make complains normally, but stops complaining with --disable-dmg
>> or --disable-bzip2.)
> 
> Thanks!
> 


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