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Re: [PATCH v3 2/2] quorum: Implement bdrv_co_pwrite_zeroes()

From: Max Reitz
Subject: Re: [PATCH v3 2/2] quorum: Implement bdrv_co_pwrite_zeroes()
Date: Fri, 13 Nov 2020 12:49:04 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0

On 11.11.20 17:53, Alberto Garcia wrote:
This simply calls bdrv_co_pwrite_zeroes() in all children

Signed-off-by: Alberto Garcia <berto@igalia.com>
  block/quorum.c             | 18 ++++++++++++++++--
  tests/qemu-iotests/312     |  7 +++++++
  tests/qemu-iotests/312.out |  4 ++++
  3 files changed, 27 insertions(+), 2 deletions(-)

Should we set supported_zero_flags to something? I think we can at least set BDRV_REQ_NO_FALLBACK. We could also try BDRV_REQ_FUA.

diff --git a/block/quorum.c b/block/quorum.c
index 9691a9bee9..c81572f513 100644
--- a/block/quorum.c
+++ b/block/quorum.c
@@ -692,8 +692,13 @@ static void write_quorum_entry(void *opaque)
      QuorumChildRequest *sacb = &acb->qcrs[i];
sacb->bs = s->children[i]->bs;
-    sacb->ret = bdrv_co_pwritev(s->children[i], acb->offset, acb->bytes,
-                                acb->qiov, acb->flags);
+    if (acb->flags & BDRV_REQ_ZERO_WRITE) {
+        sacb->ret = bdrv_co_pwrite_zeroes(s->children[i], acb->offset,
+                                          acb->bytes, acb->flags);
+    } else {
+        sacb->ret = bdrv_co_pwritev(s->children[i], acb->offset, acb->bytes,
+                                    acb->qiov, acb->flags);
+    }

Seems unnecessary (bdrv_co_pwritev() can handle BDRV_REQ_ZERO_WRITE), but perhaps it’s good to be explicit.

      if (sacb->ret == 0) {
      } else {


diff --git a/tests/qemu-iotests/312 b/tests/qemu-iotests/312
index 1b08f1552f..93046393e7 100755
--- a/tests/qemu-iotests/312
+++ b/tests/qemu-iotests/312
@@ -114,6 +114,13 @@ $QEMU_IO -c "write -P 0 $((0x200000)) $((0x10000))" 
"$TEST_IMG.0" | _filter_qemu
  $QEMU_IO -c "write -z   $((0x200000)) $((0x30000))" "$TEST_IMG.1" | 
  $QEMU_IO -c "write -P 0 $((0x200000)) $((0x20000))" "$TEST_IMG.2" | 
+# Test 5: write data to a region and then zeroize it, doing it
+# directly on the quorum device instead of the individual images.
+# This has no effect on the end result but proves that the quorum driver
+# supports 'write -z'.
+$QEMU_IO -c "open -o $quorum" -c "write $((0x250000)) $((0x10000))" | 
+$QEMU_IO -c "open -o $quorum" -c "write -z $((0x250000)) $((0x10000))" | 

My gut would have preferred a test where the data region is larger than the zeroed region (so we can see that the first write has done something), but who cares about my gut.

I don’t mind not setting supported_zero_flags enough to warrant withholding a

Reviewed-by: Max Reitz <mreitz@redhat.com>

But I’ll give you some time to reply before I’d take this patch to block-next. (That is, unless Kevin takes it during my two-week PTO...)

  echo '### Launch the drive-mirror job'

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