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[Qemu-devel] [PATCH] Serialize qcow2 writes
From: |
Avi Kivity |
Subject: |
[Qemu-devel] [PATCH] Serialize qcow2 writes |
Date: |
Tue, 5 May 2009 15:40:35 +0300 |
Commit 641636d ("qcow2 corruption: Fix alloc_cluster_link_l2"; 4df8f71 on
stable-0.10) exposes a bug with concurrent allocating qcow2 writes: the
writes will trigger a call to free_any_clusters() and corrupt the image.
As a temporary workaround until a real fix is written, this patch serializes
writes to avoid the issue. With this, I can install Fedora 10 on a virtio
disk.
Signed-off-by: Avi Kivity <address@hidden>
---
block-qcow2.c | 27 ++++++++++++++++++++++++++-
1 files changed, 26 insertions(+), 1 deletions(-)
diff --git a/block-qcow2.c b/block-qcow2.c
index 1f33125..6685915 100644
--- a/block-qcow2.c
+++ b/block-qcow2.c
@@ -157,6 +157,8 @@ typedef struct BDRVQcowState {
int snapshots_size;
int nb_snapshots;
QCowSnapshot *snapshots;
+ int write_in_progress;
+ TAILQ_HEAD(QCow2DeferredWrites, QCowAIOCB) deferred_writes;
} BDRVQcowState;
static int decompress_cluster(BDRVQcowState *s, uint64_t cluster_offset);
@@ -371,6 +373,9 @@ static int qcow_open(BlockDriverState *bs, const char
*filename, int flags)
if (qcow_read_snapshots(bs) < 0)
goto fail;
+ s->write_in_progress = 0;
+ TAILQ_INIT(&s->deferred_writes);
+
#ifdef DEBUG_ALLOC
check_refcounts(bs);
#endif
@@ -1274,6 +1279,7 @@ typedef struct QCowAIOCB {
QEMUIOVector hd_qiov;
QEMUBH *bh;
QCowL2Meta l2meta;
+ TAILQ_ENTRY(QCowAIOCB) deferred_writes_link;
} QCowAIOCB;
static void qcow_aio_read_cb(void *opaque, int ret);
@@ -1439,6 +1445,8 @@ static BlockDriverAIOCB *qcow_aio_readv(BlockDriverState
*bs,
return &acb->common;
}
+static void fire_deferred_writes(BDRVQcowState *s);
+
static void qcow_aio_write_cb(void *opaque, int ret)
{
QCowAIOCB *acb = opaque;
@@ -1509,6 +1517,21 @@ done:
qemu_vfree(acb->orig_buf);
acb->common.cb(acb->common.opaque, ret);
qemu_aio_release(acb);
+
+ s->write_in_progress = 0;
+ fire_deferred_writes(s);
+}
+
+static void fire_deferred_writes(BDRVQcowState *s)
+{
+ QCowAIOCB *acb;
+
+ if (!s->write_in_progress && !TAILQ_EMPTY(&s->deferred_writes)) {
+ s->write_in_progress = 1;
+ acb = TAILQ_FIRST(&s->deferred_writes);
+ TAILQ_REMOVE(&s->deferred_writes, acb, deferred_writes_link);
+ qcow_aio_write_cb(acb, 0);
+ }
}
static BlockDriverAIOCB *qcow_aio_writev(BlockDriverState *bs,
@@ -1524,7 +1547,9 @@ static BlockDriverAIOCB *qcow_aio_writev(BlockDriverState
*bs,
if (!acb)
return NULL;
- qcow_aio_write_cb(acb, 0);
+ TAILQ_INSERT_TAIL(&s->deferred_writes, acb, deferred_writes_link);
+ fire_deferred_writes(s);
+
return &acb->common;
}
--
1.6.1.1
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