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From fb4f98330be87d3272d91c354843eadc6db8fc73 Mon Sep 17 00:00:00 2001
From: Kevin Wolf <kwolf@redhat.com>
Date: Thu, 12 Jul 2018 14:42:57 +0200
Subject: [PATCH 212/268] block: Use tracked request for truncate

RH-Author: Kevin Wolf <kwolf@redhat.com>
Message-id: <20180712144258.17303-6-kwolf@redhat.com>
Patchwork-id: 81326
O-Subject: [RHV-7.6 qemu-kvm-rhev PATCH 5/6] block: Use tracked request for truncate
Bugzilla: 1595173
RH-Acked-by: Max Reitz <mreitz@redhat.com>
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: John Snow <jsnow@redhat.com>

When growing an image, block drivers (especially protocol drivers) may
initialise the newly added area. I/O requests to the same area need to
wait for this initialisation to be completed so that data writes don't
get overwritten and reads don't read uninitialised data.

To avoid overhead in the fast I/O path by adding new locking in the
protocol drivers and to restrict the impact to requests that actually
touch the new area, reuse the existing tracked request infrastructure in
block/io.c and mark all discard requests as serialising.

With this change, it is safe for protocol drivers to make
.bdrv_co_truncate actually asynchronous.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
(cherry picked from commit 1bc5f09f2e1b2be8f6f737b8d5352b438fc41492)
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 block/io.c                | 25 +++++++++++++++++++++++++
 include/block/block_int.h |  1 +
 2 files changed, 26 insertions(+)

diff --git a/block/io.c b/block/io.c
index 32a82e3..ad8afc0 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2948,6 +2948,8 @@ int coroutine_fn bdrv_co_truncate(BdrvChild *child, int64_t offset,
 {
     BlockDriverState *bs = child->bs;
     BlockDriver *drv = bs->drv;
+    BdrvTrackedRequest req;
+    int64_t old_size, new_bytes;
     int ret;
 
     assert(child->perm & BLK_PERM_RESIZE);
@@ -2962,7 +2964,28 @@ int coroutine_fn bdrv_co_truncate(BdrvChild *child, int64_t offset,
         return -EINVAL;
     }
 
+    old_size = bdrv_getlength(bs);
+    if (old_size < 0) {
+        error_setg_errno(errp, -old_size, "Failed to get old image size");
+        return old_size;
+    }
+
+    if (offset > old_size) {
+        new_bytes = offset - old_size;
+    } else {
+        new_bytes = 0;
+    }
+
     bdrv_inc_in_flight(bs);
+    tracked_request_begin(&req, bs, offset, new_bytes, BDRV_TRACKED_TRUNCATE);
+
+    /* If we are growing the image and potentially using preallocation for the
+     * new area, we need to make sure that no write requests are made to it
+     * concurrently or they might be overwritten by preallocation. */
+    if (new_bytes) {
+        mark_request_serialising(&req, 1);
+        wait_serialising_requests(&req);
+    }
 
     if (!drv->bdrv_co_truncate) {
         if (bs->file && drv->is_filter) {
@@ -2996,7 +3019,9 @@ int coroutine_fn bdrv_co_truncate(BdrvChild *child, int64_t offset,
     atomic_inc(&bs->write_gen);
 
 out:
+    tracked_request_end(&req);
     bdrv_dec_in_flight(bs);
+
     return ret;
 }
 
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 6a844ec..27e168f 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -63,6 +63,7 @@ enum BdrvTrackedRequestType {
     BDRV_TRACKED_READ,
     BDRV_TRACKED_WRITE,
     BDRV_TRACKED_DISCARD,
+    BDRV_TRACKED_TRUNCATE,
 };
 
 typedef struct BdrvTrackedRequest {
-- 
1.8.3.1