[v3] Make blockdev-mirror dest sparse in more cases

[PATCH v3 02/11] file-posix, gluster: Handle zero block status hint better

Eric Blake posted 11 patches 5 months, 1 week ago

Diff against v1 v2
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Maintainers: Kevin Wolf <kwolf@redhat.com>, Hanna Reitz <hreitz@redhat.com>, John Snow <jsnow@redhat.com>, Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>, Stefan Hajnoczi <stefanha@redhat.com>, Fam Zheng <fam@euphon.net>, Ronnie Sahlberg <ronniesahlberg@gmail.com>, Paolo Bonzini <pbonzini@redhat.com>, Peter Lieven <pl@dlhnet.de>, Eric Blake <eblake@redhat.com>, "Denis V. Lunev" <den@openvz.org>, Alberto Garcia <berto@igalia.com>, Ilya Dryomov <idryomov@gmail.com>, Stefan Weil <sw@weilnetz.de>, Markus Armbruster <armbru@redhat.com>

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[PATCH v3 02/11] file-posix, gluster: Handle zero block status hint better

Posted by Eric Blake 5 months, 1 week ago

Although the previous patch to change 'bool want_zero' into a bitmask
made no semantic change, it is now time to differentiate.  When the
caller specifically wants to know what parts of the file read as zero,
we need to use lseek and actually reporting holes, rather than
short-circuiting and advertising full allocation.

This change will be utilized in later patches to let mirroring
optimize for the case when the destination already reads as zeroes.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 block/file-posix.c | 3 ++-
 block/gluster.c    | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/block/file-posix.c b/block/file-posix.c
index 91deb5bf5af..575cbfba07d 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -3217,7 +3217,8 @@ static int coroutine_fn raw_co_block_status(BlockDriverState *bs,
         return ret;
     }

-    if (mode != BDRV_WANT_PRECISE) {
+    if (!(mode & BDRV_WANT_ZERO)) {
+        /* There is no backing file - all bytes are allocated in this file.  */
         *pnum = bytes;
         *map = offset;
         *file = bs;
diff --git a/block/gluster.c b/block/gluster.c
index 8197b0ecefa..e702666cbce 100644
--- a/block/gluster.c
+++ b/block/gluster.c
@@ -1482,7 +1482,7 @@ static int coroutine_fn qemu_gluster_co_block_status(BlockDriverState *bs,
         return ret;
     }

-    if (mode != BDRV_WANT_PRECISE) {
+    if (!(mode & BDRV_WANT_ZERO)) {
         *pnum = bytes;
         *map = offset;
         *file = bs;
-- 
2.49.0