Re: [PATCH v2 2/6] blockdev: Split off basic bitmap operations for qemu-img

[Eric Blake <eblake@redhat.com>]

On 4/30/20 8:59 AM, Max Reitz wrote:
> On 21.04.20 23:20, Eric Blake wrote:
>> Upcoming patches want to add some basic bitmap manipulation abilities
>> to qemu-img.  But blockdev.o is too heavyweight to link into qemu-img
>> (among other things, it would drag in block jobs and transaction
>> support - qemu-img does offline manipulation, where atomicity is less
>> important because there are no concurrent modifications to compete
>> with), so it's time to split off the bare bones of what we will need
>> into a new file blockbitmaps.o.
>>
>> In addition to exposing 6 QMP commands for use by qemu-img (add,
>> remove, clear, enable, disable, merge), this also has to export three
>> previously-static functions for use by blockdev.c transactions.
>>
>> Signed-off-by: Eric Blake <eblake@redhat.com>
>> ---
>>   Makefile.objs             |   2 +-
>>   include/sysemu/blockdev.h |  14 ++
>>   blockbitmaps.c            | 324 ++++++++++++++++++++++++++++++++++++++
> 
> Hm.  Can we get a better name?  blockdev-bitmaps.c, for example?

Sure, I'm open to bike-shed suggestions.  I'd also _really_ love to make 
the new file NOT live in the top-level, but that's a harder task that 
I'm not sure how to do (it's easy to tweak Makefile.objs for another 
file in the same directory, but harder to see through the magic to 
figure out how to relocate things).

> 
>>   blockdev.c                | 293 ----------------------------------
>>   MAINTAINERS               |   1 +
>>   5 files changed, 340 insertions(+), 294 deletions(-)
>>   create mode 100644 blockbitmaps.c
> 
> [...]
> 
>> diff --git a/include/sysemu/blockdev.h b/include/sysemu/blockdev.h
>> index a86d99b3d875..523b7493b1cd 100644
>> --- a/include/sysemu/blockdev.h
>> +++ b/include/sysemu/blockdev.h
>> @@ -57,4 +57,18 @@ QemuOpts *drive_add(BlockInterfaceType type, int index, const char *file,
>>   DriveInfo *drive_new(QemuOpts *arg, BlockInterfaceType block_default_type,
>>                        Error **errp);
>>
>> +BdrvDirtyBitmap *block_dirty_bitmap_lookup(const char *node,
>> +                                           const char *name,
>> +                                           BlockDriverState **pbs,
>> +                                           Error **errp);
>> +BdrvDirtyBitmap *do_block_dirty_bitmap_remove(const char *node,
>> +                                              const char *name, bool release,
>> +                                              BlockDriverState **bitmap_bs,
>> +                                              Error **errp);
>> +BdrvDirtyBitmap *do_block_dirty_bitmap_merge(const char *node,
>> +                                             const char *target,
>> +                                             BlockDirtyBitmapMergeSourceList *bitmaps,
>> +                                             HBitmap **backup, Error **errp);
> 
> Putting do_* functions into a normal header seems a bit weird.  Would
> these fit better into block_int.h?

I don't care which header gets them, as long as things compile. 
block_int.h seems reasonable, so I can try that.  I also wonder if I 
should rename them at all (at which point, maybe I split this into two 
patches - one doing the rename, the other doing the file motion).


>> +++ b/MAINTAINERS
>> @@ -1989,6 +1989,7 @@ T: git https://github.com/jnsnow/qemu.git jobs
>>   Block QAPI, monitor, command line
>>   M: Markus Armbruster <armbru@redhat.com>
>>   S: Supported
>> +F: blockbitmaps.c
> 
> The natural choice for something split off of blockdev.c, but I wonder
> if the Dirty Bitmaps section wouldn’t be a better fit.

Or maybe even both?


-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org