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Re: [PATCH 04/17] block: Improve documentation of .bdrv_has_zero_init

From: Vladimir Sementsov-Ogievskiy
Subject: Re: [PATCH 04/17] block: Improve documentation of .bdrv_has_zero_init
Date: Tue, 4 Feb 2020 18:03:09 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1

31.01.2020 20:44, Eric Blake wrote:
Several drivers supply .bdrv_has_zero_init that returns 1, but lack
the .bdrv_has_zero_init_truncate callback (parallels and qed outright,
vdi in some scenarios).  A literal reading of the existing
documentation says such drivers are broken, because
bdrv_has_zero_init_truncate() defaults to zero if the callback is
missing; but in practice, the tie between the two functions is only
relevant when truncate is supported.  Clarify the documentation to
make it obvious that this is okay.

Fixes: 1dcaf527
Signed-off-by: Eric Blake <address@hidden>
  include/block/block_int.h | 3 ++-
  1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/block/block_int.h b/include/block/block_int.h
index 640fb82c789e..77ab45dc87cf 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -444,7 +444,8 @@ struct BlockDriver {
       * Returns 1 if newly created images are guaranteed to contain only
       * zeros, 0 otherwise.
-     * Must return 0 if .bdrv_has_zero_init_truncate() returns 0.
+     * Must return 0 if .bdrv_co_truncate is set and
+     * .bdrv_has_zero_init_truncate() returns 0.
      int (*bdrv_has_zero_init)(BlockDriverState *bs);

I doubt, shouldn't 1dcaf527 be fixed by adding all needed 
bdrv_has_zero_init_truncate functions?

(sorry, I started to dig in the code and patches around 
bdrv_has_zero_init_truncate and tired :(.,
 hope Max will comment this).

Best regards,

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