From 5ad7c32387034a02c9a932018e60580872431db9 Mon Sep 17 00:00:00 2001
From: Maxim Levitsky <mlevitsk@redhat.com>
Date: Wed, 5 Jun 2019 13:56:58 +0200
Subject: [PATCH 10/23] block: Add BDRV_REQ_NO_FALLBACK

RH-Author: Maxim Levitsky <mlevitsk@redhat.com>
Message-id: <20190605135705.24526-3-mlevitsk@redhat.com>
Patchwork-id: 88557
O-Subject: [RHEL-7.7 qemu-kvm-rhev PATCH 2/9] block: Add BDRV_REQ_NO_FALLBACK
Bugzilla: 1648622
RH-Acked-by: Max Reitz <mreitz@redhat.com>
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: John Snow <jsnow@redhat.com>

From: Kevin Wolf <kwolf@redhat.com>

For qemu-img convert, we want an operation that zeroes out the whole
image if this can be done efficiently, but that returns an error
otherwise so we don't write explicit zeroes and immediately overwrite
them with the real data, potentially doubling the amount of data to be
written.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Acked-by: Eric Blake <eblake@redhat.com>

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1648622

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
(Cherry picked from fe0480d6294270ff0d6fb60e66bb725a6aad2043)

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 block/io.c            | 12 +++++++++++-
 include/block/block.h |  7 ++++++-
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/block/io.c b/block/io.c
index 18bf3c2..26c4075 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1029,6 +1029,7 @@ static int coroutine_fn bdrv_driver_preadv(BlockDriverState *bs,
     unsigned int nb_sectors;
 
     assert(!(flags & ~BDRV_REQ_MASK));
+    assert(!(flags & BDRV_REQ_NO_FALLBACK));
 
     if (!drv) {
         return -ENOMEDIUM;
@@ -1074,6 +1075,7 @@ static int coroutine_fn bdrv_driver_pwritev(BlockDriverState *bs,
     int ret;
 
     assert(!(flags & ~BDRV_REQ_MASK));
+    assert(!(flags & BDRV_REQ_NO_FALLBACK));
 
     if (!drv) {
         return -ENOMEDIUM;
@@ -1499,6 +1501,10 @@ static int coroutine_fn bdrv_co_do_pwrite_zeroes(BlockDriverState *bs,
         return -ENOMEDIUM;
     }
 
+    if ((flags & ~bs->supported_zero_flags) & BDRV_REQ_NO_FALLBACK) {
+        return -ENOTSUP;
+    }
+
     assert(alignment % bs->bl.request_alignment == 0);
     head = offset % alignment;
     tail = (offset + bytes) % alignment;
@@ -1542,7 +1548,7 @@ static int coroutine_fn bdrv_co_do_pwrite_zeroes(BlockDriverState *bs,
             assert(!bs->supported_zero_flags);
         }
 
-        if (ret == -ENOTSUP) {
+        if (ret == -ENOTSUP && !(flags & BDRV_REQ_NO_FALLBACK)) {
             /* Fall back to bounce buffer if write zeroes is unsupported */
             BdrvRequestFlags write_flags = flags & ~BDRV_REQ_ZERO_WRITE;
 
@@ -2973,6 +2979,10 @@ static int coroutine_fn bdrv_co_copy_range_internal(
     BdrvTrackedRequest req;
     int ret;
 
+    /* TODO We can support BDRV_REQ_NO_FALLBACK here */
+    assert(!(read_flags & BDRV_REQ_NO_FALLBACK));
+    assert(!(write_flags & BDRV_REQ_NO_FALLBACK));
+
     if (!dst || !dst->bs) {
         return -ENOMEDIUM;
     }
diff --git a/include/block/block.h b/include/block/block.h
index 5f40140..33fb60c 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -82,8 +82,13 @@ typedef enum {
      */
     BDRV_REQ_SERIALISING        = 0x80,
 
+    /* Execute the request only if the operation can be offloaded or otherwise
+     * be executed efficiently, but return an error instead of using a slow
+     * fallback. */
+    BDRV_REQ_NO_FALLBACK        = 0x100,
+
     /* Mask of valid flags */
-    BDRV_REQ_MASK               = 0xff,
+    BDRV_REQ_MASK               = 0x1ff,
 } BdrvRequestFlags;
 
 typedef struct BlockSizes {
-- 
1.8.3.1