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Blame SOURCES/kvm-block-vhdx-log-parsing-replay-and-flush-support.patch

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From 457fd5fdb8a089eec09fc21e06ce3099633a248a Mon Sep 17 00:00:00 2001
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From: Jeffrey Cody <jcody@redhat.com>
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Date: Wed, 20 Nov 2013 19:43:57 +0100
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Subject: [PATCH 14/25] block: vhdx - log parsing, replay, and flush support
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RH-Author: Jeffrey Cody <jcody@redhat.com>
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Message-id: <a64a5d0ec84826a20a9fb23dce611793afd19cd5.1384975172.git.jcody@redhat.com>
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Patchwork-id: 55807
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O-Subject: [RHEL7 qemu-kvm PATCH 14/26] block: vhdx - log parsing, replay, and flush support
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Bugzilla: 879234
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
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RH-Acked-by: Fam Zheng <famz@redhat.com>
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This adds support for VHDX v0 logs, as specified in Microsoft's
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VHDX Specification Format v1.00:
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https://www.microsoft.com/en-us/download/details.aspx?id=34750
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The following support is added:
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* Log parsing, and validation - validate that an existing log
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  is correct.
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* Log search - search through an existing log, to find any valid
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  sequence of entries.
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* Log replay and flush - replay an existing log, and flush/clear
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  the log when complete.
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The VHDX log is a circular buffer, with elements (sectors) of 4KB.
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A log entry is a variably-length number of sectors, that is
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comprised of a header and 'descriptors', that describe each sector.
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A log may contain multiple entries, know as a log sequence.  In a log
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sequence, each log entry immediately follows the previous entry, with an
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incrementing sequence number.  There can only ever be one active and
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valid sequence in the log.
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Each log entry must match the file log GUID in order to be valid (along
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with other criteria).  Once we have flushed all valid log entries, we
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marked the file log GUID to be zero, which indicates a buffer with no
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valid entries.
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Signed-off-by: Jeff Cody <jcody@redhat.com>
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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(cherry picked from commit 0a43a1b5d7c33208120eeb2d98ebb9ab15dc2c87)
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---
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 block/Makefile.objs |   2 +-
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 block/vhdx-log.c    | 728 ++++++++++++++++++++++++++++++++++++++++++++++++++++
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 block/vhdx.c        |  65 +----
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 block/vhdx.h        |   7 +-
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 4 files changed, 749 insertions(+), 53 deletions(-)
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 create mode 100644 block/vhdx-log.c
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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 block/Makefile.objs |    2 +-
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 block/vhdx-log.c    |  728 +++++++++++++++++++++++++++++++++++++++++++++++++++
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 block/vhdx.c        |   65 +----
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 block/vhdx.h        |    7 +-
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 4 files changed, 749 insertions(+), 53 deletions(-)
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 create mode 100644 block/vhdx-log.c
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diff --git a/block/Makefile.objs b/block/Makefile.objs
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index a7b3b87..84dd57f 100644
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--- a/block/Makefile.objs
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+++ b/block/Makefile.objs
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@@ -2,7 +2,7 @@ block-obj-y += raw.o cow.o qcow.o vdi.o vmdk.o cloop.o dmg.o bochs.o vpc.o vvfat
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 block-obj-y += qcow2.o qcow2-refcount.o qcow2-cluster.o qcow2-snapshot.o qcow2-cache.o
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 block-obj-y += qed.o qed-gencb.o qed-l2-cache.o qed-table.o qed-cluster.o
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 block-obj-y += qed-check.o
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-block-obj-$(CONFIG_VHDX) += vhdx.o vhdx-endian.o
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+block-obj-$(CONFIG_VHDX) += vhdx.o vhdx-endian.o vhdx-log.o
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 block-obj-y += parallels.o blkdebug.o blkverify.o
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 block-obj-y += snapshot.o qapi.o
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 block-obj-$(CONFIG_WIN32) += raw-win32.o win32-aio.o
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diff --git a/block/vhdx-log.c b/block/vhdx-log.c
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new file mode 100644
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index 0000000..0284729
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--- /dev/null
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+++ b/block/vhdx-log.c
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@@ -0,0 +1,728 @@
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+/*
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+ * Block driver for Hyper-V VHDX Images
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+ *
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+ * Copyright (c) 2013 Red Hat, Inc.,
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+ *
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+ * Authors:
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+ *  Jeff Cody <jcody@redhat.com>
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+ *
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+ *  This is based on the "VHDX Format Specification v1.00", published 8/25/2012
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+ *  by Microsoft:
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+ *      https://www.microsoft.com/en-us/download/details.aspx?id=34750
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+ *
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+ * This file covers the functionality of the metadata log writing, parsing, and
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+ * replay.
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+ *
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+ * This work is licensed under the terms of the GNU LGPL, version 2 or later.
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+ * See the COPYING.LIB file in the top-level directory.
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+ *
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+ */
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+#include "qemu-common.h"
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+#include "block/block_int.h"
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+#include "qemu/module.h"
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+#include "block/vhdx.h"
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+
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+
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+typedef struct VHDXLogSequence {
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+    bool valid;
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+    uint32_t count;
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+    VHDXLogEntries log;
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+    VHDXLogEntryHeader hdr;
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+} VHDXLogSequence;
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+
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+typedef struct VHDXLogDescEntries {
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+    VHDXLogEntryHeader hdr;
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+    VHDXLogDescriptor desc[];
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+} VHDXLogDescEntries;
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+
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+static const MSGUID zero_guid = { 0 };
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+
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+/* The log located on the disk is circular buffer containing
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+ * sectors of 4096 bytes each.
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+ *
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+ * It is assumed for the read/write functions below that the
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+ * circular buffer scheme uses a 'one sector open' to indicate
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+ * the buffer is full.  Given the validation methods used for each
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+ * sector, this method should be compatible with other methods that
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+ * do not waste a sector.
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+ */
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+
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+
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+/* Allow peeking at the hdr entry at the beginning of the current
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+ * read index, without advancing the read index */
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+static int vhdx_log_peek_hdr(BlockDriverState *bs, VHDXLogEntries *log,
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+                             VHDXLogEntryHeader *hdr)
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+{
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+    int ret = 0;
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+    uint64_t offset;
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+    uint32_t read;
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+
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+    assert(hdr != NULL);
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+
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+    /* peek is only supported on sector boundaries */
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+    if (log->read % VHDX_LOG_SECTOR_SIZE) {
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+        ret = -EFAULT;
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+        goto exit;
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+    }
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+
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+    read = log->read;
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+    /* we are guaranteed that a) log sectors are 4096 bytes,
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+     * and b) the log length is a multiple of 1MB. So, there
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+     * is always a round number of sectors in the buffer */
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+    if ((read + sizeof(VHDXLogEntryHeader)) > log->length) {
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+        read = 0;
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+    }
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+
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+    if (read == log->write) {
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+        ret = -EINVAL;
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+        goto exit;
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+    }
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+
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+    offset = log->offset + read;
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+
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+    ret = bdrv_pread(bs->file, offset, hdr, sizeof(VHDXLogEntryHeader));
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+    if (ret < 0) {
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+        goto exit;
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+    }
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+
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+exit:
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+    return ret;
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+}
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+
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+/* Index increment for log, based on sector boundaries */
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+static int vhdx_log_inc_idx(uint32_t idx, uint64_t length)
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+{
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+    idx += VHDX_LOG_SECTOR_SIZE;
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+    /* we are guaranteed that a) log sectors are 4096 bytes,
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+     * and b) the log length is a multiple of 1MB. So, there
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+     * is always a round number of sectors in the buffer */
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+    return idx >= length ? 0 : idx;
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+}
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+
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+
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+/* Reset the log to empty */
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+static void vhdx_log_reset(BlockDriverState *bs, BDRVVHDXState *s)
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+{
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+    MSGUID guid = { 0 };
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+    s->log.read = s->log.write = 0;
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+    /* a log guid of 0 indicates an empty log to any parser of v0
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+     * VHDX logs */
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+    vhdx_update_headers(bs, s, false, &guid);
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+}
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+
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+/* Reads num_sectors from the log (all log sectors are 4096 bytes),
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+ * into buffer 'buffer'.  Upon return, *sectors_read will contain
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+ * the number of sectors successfully read.
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+ *
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+ * It is assumed that 'buffer' is already allocated, and of sufficient
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+ * size (i.e. >= 4096*num_sectors).
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+ *
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+ * If 'peek' is true, then the tail (read) pointer for the circular buffer is
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+ * not modified.
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+ *
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+ * 0 is returned on success, -errno otherwise.  */
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+static int vhdx_log_read_sectors(BlockDriverState *bs, VHDXLogEntries *log,
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+                                 uint32_t *sectors_read, void *buffer,
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+                                 uint32_t num_sectors, bool peek)
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+{
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+    int ret = 0;
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+    uint64_t offset;
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+    uint32_t read;
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+
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+    read = log->read;
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+
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+    *sectors_read = 0;
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+    while (num_sectors) {
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+        if (read == log->write) {
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+            /* empty */
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+            break;
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+        }
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+        offset = log->offset + read;
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+
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+        ret = bdrv_pread(bs->file, offset, buffer, VHDX_LOG_SECTOR_SIZE);
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+        if (ret < 0) {
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+            goto exit;
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+        }
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+        read = vhdx_log_inc_idx(read, log->length);
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+
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+        *sectors_read = *sectors_read + 1;
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+        num_sectors--;
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+    }
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+
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+exit:
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+    if (!peek) {
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+        log->read = read;
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+    }
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+    return ret;
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+}
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+
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+/* Validates a log entry header */
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+static bool vhdx_log_hdr_is_valid(VHDXLogEntries *log, VHDXLogEntryHeader *hdr,
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+                                  BDRVVHDXState *s)
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+{
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+    int valid = false;
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+
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+    if (memcmp(&hdr->signature, "loge", 4)) {
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+        goto exit;
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+    }
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+
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+    /* if the individual entry length is larger than the whole log
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+     * buffer, that is obviously invalid */
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+    if (log->length < hdr->entry_length) {
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+        goto exit;
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+    }
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+
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+    /* length of entire entry must be in units of 4KB (log sector size) */
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+    if (hdr->entry_length % (VHDX_LOG_SECTOR_SIZE)) {
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+        goto exit;
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+    }
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+
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+    /* per spec, sequence # must be > 0 */
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+    if (hdr->sequence_number == 0) {
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+        goto exit;
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+    }
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+
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+    /* log entries are only valid if they match the file-wide log guid
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+     * found in the active header */
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+    if (!guid_eq(hdr->log_guid, s->headers[s->curr_header]->log_guid)) {
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+        goto exit;
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+    }
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+
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+    if (hdr->descriptor_count * sizeof(VHDXLogDescriptor) > hdr->entry_length) {
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+        goto exit;
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+    }
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+
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+    valid = true;
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+
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+exit:
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+    return valid;
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+}
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+
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+/*
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+ * Given a log header, this will validate that the descriptors and the
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+ * corresponding data sectors (if applicable)
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+ *
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+ * Validation consists of:
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+ *      1. Making sure the sequence numbers matches the entry header
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+ *      2. Verifying a valid signature ('zero' or 'desc' for descriptors)
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+ *      3. File offset field is a multiple of 4KB
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+ *      4. If a data descriptor, the corresponding data sector
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+ *         has its signature ('data') and matching sequence number
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+ *
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+ * @desc: the data buffer containing the descriptor
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+ * @hdr:  the log entry header
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+ *
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+ * Returns true if valid
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+ */
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+static bool vhdx_log_desc_is_valid(VHDXLogDescriptor *desc,
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+                                   VHDXLogEntryHeader *hdr)
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+{
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+    bool ret = false;
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+
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+    if (desc->sequence_number != hdr->sequence_number) {
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+        goto exit;
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+    }
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+    if (desc->file_offset % VHDX_LOG_SECTOR_SIZE) {
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+        goto exit;
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+    }
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+
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+    if (!memcmp(&desc->signature, "zero", 4)) {
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+        if (desc->zero_length % VHDX_LOG_SECTOR_SIZE == 0) {
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+            /* valid */
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+            ret = true;
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+        }
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+    } else if (!memcmp(&desc->signature, "desc", 4)) {
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+            /* valid */
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+            ret = true;
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+    }
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+
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+exit:
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+    return ret;
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+}
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+
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+
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+/* Prior to sector data for a log entry, there is the header
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+ * and the descriptors referenced in the header:
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+ *
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+ * [] = 4KB sector
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+ *
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+ * [ hdr, desc ][   desc   ][ ... ][ data ][ ... ]
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+ *
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+ * The first sector in a log entry has a 64 byte header, and
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+ * up to 126 32-byte descriptors.  If more descriptors than
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+ * 126 are required, then subsequent sectors can have up to 128
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+ * descriptors.  Each sector is 4KB.  Data follows the descriptor
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+ * sectors.
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+ *
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+ * This will return the number of sectors needed to encompass
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+ * the passed number of descriptors in desc_cnt.
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+ *
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+ * This will never return 0, even if desc_cnt is 0.
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+ */
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+static int vhdx_compute_desc_sectors(uint32_t desc_cnt)
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+{
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+    uint32_t desc_sectors;
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+
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+    desc_cnt += 2; /* account for header in first sector */
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+    desc_sectors = desc_cnt / 128;
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+    if (desc_cnt % 128) {
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+        desc_sectors++;
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+    }
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+
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+    return desc_sectors;
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+}
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+
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+
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+/* Reads the log header, and subsequent descriptors (if any).  This
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+ * will allocate all the space for buffer, which must be NULL when
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+ * passed into this function. Each descriptor will also be validated,
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+ * and error returned if any are invalid. */
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+static int vhdx_log_read_desc(BlockDriverState *bs, BDRVVHDXState *s,
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+                              VHDXLogEntries *log, VHDXLogDescEntries **buffer)
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+{
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+    int ret = 0;
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+    uint32_t desc_sectors;
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+    uint32_t sectors_read;
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+    VHDXLogEntryHeader hdr;
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+    VHDXLogDescEntries *desc_entries = NULL;
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+    int i;
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+
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+    assert(*buffer == NULL);
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+
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+    ret = vhdx_log_peek_hdr(bs, log, &hdr);
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+    if (ret < 0) {
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+        goto exit;
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+    }
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+    vhdx_log_entry_hdr_le_import(&hdr);
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+    if (vhdx_log_hdr_is_valid(log, &hdr, s) == false) {
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+        ret = -EINVAL;
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+        goto exit;
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+    }
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+
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+    desc_sectors = vhdx_compute_desc_sectors(hdr.descriptor_count);
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+    desc_entries = qemu_blockalign(bs, desc_sectors * VHDX_LOG_SECTOR_SIZE);
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+
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+    ret = vhdx_log_read_sectors(bs, log, &sectors_read, desc_entries,
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+                                desc_sectors, false);
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+    if (ret < 0) {
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+        goto free_and_exit;
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+    }
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+    if (sectors_read != desc_sectors) {
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+        ret = -EINVAL;
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+        goto free_and_exit;
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+    }
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+
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+    /* put in proper endianness, and validate each desc */
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+    for (i = 0; i < hdr.descriptor_count; i++) {
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+        vhdx_log_desc_le_import(&desc_entries->desc[i]);
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+        if (vhdx_log_desc_is_valid(&desc_entries->desc[i], &hdr) == false) {
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+            ret = -EINVAL;
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+            goto free_and_exit;
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+        }
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+    }
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+
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+    *buffer = desc_entries;
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+    goto exit;
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+
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+free_and_exit:
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+    qemu_vfree(desc_entries);
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+exit:
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+    return ret;
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+}
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+
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+
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+/* Flushes the descriptor described by desc to the VHDX image file.
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+ * If the descriptor is a data descriptor, than 'data' must be non-NULL,
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+ * and >= 4096 bytes (VHDX_LOG_SECTOR_SIZE), containing the data to be
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+ * written.
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+ *
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+ * Verification is performed to make sure the sequence numbers of a data
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+ * descriptor match the sequence number in the desc.
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+ *
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+ * For a zero descriptor, it may describe multiple sectors to fill with zeroes.
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+ * In this case, it should be noted that zeroes are written to disk, and the
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+ * image file is not extended as a sparse file.  */
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+static int vhdx_log_flush_desc(BlockDriverState *bs, VHDXLogDescriptor *desc,
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+                               VHDXLogDataSector *data)
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+{
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+    int ret = 0;
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+    uint64_t seq, file_offset;
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+    uint32_t offset = 0;
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+    void *buffer = NULL;
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+    uint64_t count = 1;
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+    int i;
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+
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+    buffer = qemu_blockalign(bs, VHDX_LOG_SECTOR_SIZE);
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+
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+    if (!memcmp(&desc->signature, "desc", 4)) {
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+        /* data sector */
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+        if (data == NULL) {
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+            ret = -EFAULT;
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+            goto exit;
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+        }
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+
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+        /* The sequence number of the data sector must match that
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+         * in the descriptor */
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+        seq = data->sequence_high;
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+        seq <<= 32;
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+        seq |= data->sequence_low & 0xffffffff;
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+
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+        if (seq != desc->sequence_number) {
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+            ret = -EINVAL;
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+            goto exit;
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+        }
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+
0a122b
+        /* Each data sector is in total 4096 bytes, however the first
0a122b
+         * 8 bytes, and last 4 bytes, are located in the descriptor */
0a122b
+        memcpy(buffer, &desc->leading_bytes, 8);
0a122b
+        offset += 8;
0a122b
+
0a122b
+        memcpy(buffer+offset, data->data, 4084);
0a122b
+        offset += 4084;
0a122b
+
0a122b
+        memcpy(buffer+offset, &desc->trailing_bytes, 4);
0a122b
+
0a122b
+    } else if (!memcmp(&desc->signature, "zero", 4)) {
0a122b
+        /* write 'count' sectors of sector */
0a122b
+        memset(buffer, 0, VHDX_LOG_SECTOR_SIZE);
0a122b
+        count = desc->zero_length / VHDX_LOG_SECTOR_SIZE;
0a122b
+    }
0a122b
+
0a122b
+    file_offset = desc->file_offset;
0a122b
+
0a122b
+    /* count is only > 1 if we are writing zeroes */
0a122b
+    for (i = 0; i < count; i++) {
0a122b
+        ret = bdrv_pwrite_sync(bs->file, file_offset, buffer,
0a122b
+                               VHDX_LOG_SECTOR_SIZE);
0a122b
+        if (ret < 0) {
0a122b
+            goto exit;
0a122b
+        }
0a122b
+        file_offset += VHDX_LOG_SECTOR_SIZE;
0a122b
+    }
0a122b
+
0a122b
+exit:
0a122b
+    qemu_vfree(buffer);
0a122b
+    return ret;
0a122b
+}
0a122b
+
0a122b
+/* Flush the entire log (as described by 'logs') to the VHDX image
0a122b
+ * file, and then set the log to 'empty' status once complete.
0a122b
+ *
0a122b
+ * The log entries should be validate prior to flushing */
0a122b
+static int vhdx_log_flush(BlockDriverState *bs, BDRVVHDXState *s,
0a122b
+                          VHDXLogSequence *logs)
0a122b
+{
0a122b
+    int ret = 0;
0a122b
+    int i;
0a122b
+    uint32_t cnt, sectors_read;
0a122b
+    uint64_t new_file_size;
0a122b
+    void *data = NULL;
0a122b
+    VHDXLogDescEntries *desc_entries = NULL;
0a122b
+    VHDXLogEntryHeader hdr_tmp = { 0 };
0a122b
+
0a122b
+    cnt = logs->count;
0a122b
+
0a122b
+    data = qemu_blockalign(bs, VHDX_LOG_SECTOR_SIZE);
0a122b
+
0a122b
+    ret = vhdx_user_visible_write(bs, s);
0a122b
+    if (ret < 0) {
0a122b
+        goto exit;
0a122b
+    }
0a122b
+
0a122b
+    /* each iteration represents one log sequence, which may span multiple
0a122b
+     * sectors */
0a122b
+    while (cnt--) {
0a122b
+        ret = vhdx_log_peek_hdr(bs, &logs->log, &hdr_tmp);
0a122b
+        if (ret < 0) {
0a122b
+            goto exit;
0a122b
+        }
0a122b
+        /* if the log shows a FlushedFileOffset larger than our current file
0a122b
+         * size, then that means the file has been truncated / corrupted, and
0a122b
+         * we must refused to open it / use it */
0a122b
+        if (hdr_tmp.flushed_file_offset > bdrv_getlength(bs->file)) {
0a122b
+            ret = -EINVAL;
0a122b
+            goto exit;
0a122b
+        }
0a122b
+
0a122b
+        ret = vhdx_log_read_desc(bs, s, &logs->log, &desc_entries);
0a122b
+        if (ret < 0) {
0a122b
+            goto exit;
0a122b
+        }
0a122b
+
0a122b
+        for (i = 0; i < desc_entries->hdr.descriptor_count; i++) {
0a122b
+            if (!memcmp(&desc_entries->desc[i].signature, "desc", 4)) {
0a122b
+                /* data sector, so read a sector to flush */
0a122b
+                ret = vhdx_log_read_sectors(bs, &logs->log, &sectors_read,
0a122b
+                                            data, 1, false);
0a122b
+                if (ret < 0) {
0a122b
+                    goto exit;
0a122b
+                }
0a122b
+                if (sectors_read != 1) {
0a122b
+                    ret = -EINVAL;
0a122b
+                    goto exit;
0a122b
+                }
0a122b
+            }
0a122b
+
0a122b
+            ret = vhdx_log_flush_desc(bs, &desc_entries->desc[i], data);
0a122b
+            if (ret < 0) {
0a122b
+                goto exit;
0a122b
+            }
0a122b
+        }
0a122b
+        if (bdrv_getlength(bs->file) < desc_entries->hdr.last_file_offset) {
0a122b
+            new_file_size = desc_entries->hdr.last_file_offset;
0a122b
+            if (new_file_size % (1024*1024)) {
0a122b
+                /* round up to nearest 1MB boundary */
0a122b
+                new_file_size = ((new_file_size >> 20) + 1) << 20;
0a122b
+                bdrv_truncate(bs->file, new_file_size);
0a122b
+            }
0a122b
+        }
0a122b
+        qemu_vfree(desc_entries);
0a122b
+        desc_entries = NULL;
0a122b
+    }
0a122b
+
0a122b
+    bdrv_flush(bs);
0a122b
+    /* once the log is fully flushed, indicate that we have an empty log
0a122b
+     * now.  This also sets the log guid to 0, to indicate an empty log */
0a122b
+    vhdx_log_reset(bs, s);
0a122b
+
0a122b
+exit:
0a122b
+    qemu_vfree(data);
0a122b
+    qemu_vfree(desc_entries);
0a122b
+    return ret;
0a122b
+}
0a122b
+
0a122b
+static int vhdx_validate_log_entry(BlockDriverState *bs, BDRVVHDXState *s,
0a122b
+                                   VHDXLogEntries *log, uint64_t seq,
0a122b
+                                   bool *valid, VHDXLogEntryHeader *entry)
0a122b
+{
0a122b
+    int ret = 0;
0a122b
+    VHDXLogEntryHeader hdr;
0a122b
+    void *buffer = NULL;
0a122b
+    uint32_t i, desc_sectors, total_sectors, crc;
0a122b
+    uint32_t sectors_read = 0;
0a122b
+    VHDXLogDescEntries *desc_buffer = NULL;
0a122b
+
0a122b
+    *valid = false;
0a122b
+
0a122b
+    ret = vhdx_log_peek_hdr(bs, log, &hdr);
0a122b
+    if (ret < 0) {
0a122b
+        goto inc_and_exit;
0a122b
+    }
0a122b
+
0a122b
+    vhdx_log_entry_hdr_le_import(&hdr);
0a122b
+
0a122b
+
0a122b
+    if (vhdx_log_hdr_is_valid(log, &hdr, s) == false) {
0a122b
+        goto inc_and_exit;
0a122b
+    }
0a122b
+
0a122b
+    if (seq > 0) {
0a122b
+        if (hdr.sequence_number != seq + 1) {
0a122b
+            goto inc_and_exit;
0a122b
+        }
0a122b
+    }
0a122b
+
0a122b
+    desc_sectors = vhdx_compute_desc_sectors(hdr.descriptor_count);
0a122b
+
0a122b
+    /* Read desc sectors, and calculate log checksum */
0a122b
+
0a122b
+    total_sectors = hdr.entry_length / VHDX_LOG_SECTOR_SIZE;
0a122b
+
0a122b
+
0a122b
+    /* read_desc() will incrememnt the read idx */
0a122b
+    ret = vhdx_log_read_desc(bs, s, log, &desc_buffer);
0a122b
+    if (ret < 0) {
0a122b
+        goto free_and_exit;
0a122b
+    }
0a122b
+
0a122b
+    crc = vhdx_checksum_calc(0xffffffff, (void *)desc_buffer,
0a122b
+                            desc_sectors * VHDX_LOG_SECTOR_SIZE, 4);
0a122b
+    crc ^= 0xffffffff;
0a122b
+
0a122b
+    buffer = qemu_blockalign(bs, VHDX_LOG_SECTOR_SIZE);
0a122b
+    if (total_sectors > desc_sectors) {
0a122b
+        for (i = 0; i < total_sectors - desc_sectors; i++) {
0a122b
+            sectors_read = 0;
0a122b
+            ret = vhdx_log_read_sectors(bs, log, &sectors_read, buffer,
0a122b
+                                        1, false);
0a122b
+            if (ret < 0 || sectors_read != 1) {
0a122b
+                goto free_and_exit;
0a122b
+            }
0a122b
+            crc = vhdx_checksum_calc(crc, buffer, VHDX_LOG_SECTOR_SIZE, -1);
0a122b
+            crc ^= 0xffffffff;
0a122b
+        }
0a122b
+    }
0a122b
+    crc ^= 0xffffffff;
0a122b
+    if (crc != desc_buffer->hdr.checksum) {
0a122b
+        goto free_and_exit;
0a122b
+    }
0a122b
+
0a122b
+    *valid = true;
0a122b
+    *entry = hdr;
0a122b
+    goto free_and_exit;
0a122b
+
0a122b
+inc_and_exit:
0a122b
+    log->read = vhdx_log_inc_idx(log->read, log->length);
0a122b
+
0a122b
+free_and_exit:
0a122b
+    qemu_vfree(buffer);
0a122b
+    qemu_vfree(desc_buffer);
0a122b
+    return ret;
0a122b
+}
0a122b
+
0a122b
+/* Search through the log circular buffer, and find the valid, active
0a122b
+ * log sequence, if any exists
0a122b
+ * */
0a122b
+static int vhdx_log_search(BlockDriverState *bs, BDRVVHDXState *s,
0a122b
+                           VHDXLogSequence *logs)
0a122b
+{
0a122b
+    int ret = 0;
0a122b
+    uint32_t tail;
0a122b
+    bool seq_valid = false;
0a122b
+    VHDXLogSequence candidate = { 0 };
0a122b
+    VHDXLogEntryHeader hdr = { 0 };
0a122b
+    VHDXLogEntries curr_log;
0a122b
+
0a122b
+    memcpy(&curr_log, &s->log, sizeof(VHDXLogEntries));
0a122b
+    curr_log.write = curr_log.length;   /* assume log is full */
0a122b
+    curr_log.read = 0;
0a122b
+
0a122b
+
0a122b
+    /* now we will go through the whole log sector by sector, until
0a122b
+     * we find a valid, active log sequence, or reach the end of the
0a122b
+     * log buffer */
0a122b
+    for (;;) {
0a122b
+        uint64_t curr_seq = 0;
0a122b
+        VHDXLogSequence current = { 0 };
0a122b
+
0a122b
+        tail = curr_log.read;
0a122b
+
0a122b
+        ret = vhdx_validate_log_entry(bs, s, &curr_log, curr_seq,
0a122b
+                                      &seq_valid, &hdr);
0a122b
+        if (ret < 0) {
0a122b
+            goto exit;
0a122b
+        }
0a122b
+
0a122b
+        if (seq_valid) {
0a122b
+            current.valid     = true;
0a122b
+            current.log       = curr_log;
0a122b
+            current.log.read  = tail;
0a122b
+            current.log.write = curr_log.read;
0a122b
+            current.count     = 1;
0a122b
+            current.hdr       = hdr;
0a122b
+
0a122b
+
0a122b
+            for (;;) {
0a122b
+                ret = vhdx_validate_log_entry(bs, s, &curr_log, curr_seq,
0a122b
+                                              &seq_valid, &hdr);
0a122b
+                if (ret < 0) {
0a122b
+                    goto exit;
0a122b
+                }
0a122b
+                if (seq_valid == false) {
0a122b
+                    break;
0a122b
+                }
0a122b
+                current.log.write = curr_log.read;
0a122b
+                current.count++;
0a122b
+
0a122b
+                curr_seq = hdr.sequence_number;
0a122b
+            }
0a122b
+        }
0a122b
+
0a122b
+        if (current.valid) {
0a122b
+            if (candidate.valid == false ||
0a122b
+                current.hdr.sequence_number > candidate.hdr.sequence_number) {
0a122b
+                candidate = current;
0a122b
+            }
0a122b
+        }
0a122b
+
0a122b
+        if (curr_log.read < tail) {
0a122b
+            break;
0a122b
+        }
0a122b
+    }
0a122b
+
0a122b
+    *logs = candidate;
0a122b
+
0a122b
+    if (candidate.valid) {
0a122b
+        /* this is the next sequence number, for writes */
0a122b
+        s->log.sequence = candidate.hdr.sequence_number + 1;
0a122b
+    }
0a122b
+
0a122b
+
0a122b
+exit:
0a122b
+    return ret;
0a122b
+}
0a122b
+
0a122b
+/* Parse the replay log.  Per the VHDX spec, if the log is present
0a122b
+ * it must be replayed prior to opening the file, even read-only.
0a122b
+ *
0a122b
+ * If read-only, we must replay the log in RAM (or refuse to open
0a122b
+ * a dirty VHDX file read-only) */
0a122b
+int vhdx_parse_log(BlockDriverState *bs, BDRVVHDXState *s, bool *flushed)
0a122b
+{
0a122b
+    int ret = 0;
0a122b
+    VHDXHeader *hdr;
0a122b
+    VHDXLogSequence logs = { 0 };
0a122b
+
0a122b
+    hdr = s->headers[s->curr_header];
0a122b
+
0a122b
+    *flushed = false;
0a122b
+
0a122b
+    /* s->log.hdr is freed in vhdx_close() */
0a122b
+    if (s->log.hdr == NULL) {
0a122b
+        s->log.hdr = qemu_blockalign(bs, sizeof(VHDXLogEntryHeader));
0a122b
+    }
0a122b
+
0a122b
+    s->log.offset = hdr->log_offset;
0a122b
+    s->log.length = hdr->log_length;
0a122b
+
0a122b
+    if (s->log.offset < VHDX_LOG_MIN_SIZE ||
0a122b
+        s->log.offset % VHDX_LOG_MIN_SIZE) {
0a122b
+        ret = -EINVAL;
0a122b
+        goto exit;
0a122b
+    }
0a122b
+
0a122b
+    /* per spec, only log version of 0 is supported */
0a122b
+    if (hdr->log_version != 0) {
0a122b
+        ret = -EINVAL;
0a122b
+        goto exit;
0a122b
+    }
0a122b
+
0a122b
+    /* If either the log guid, or log length is zero,
0a122b
+     * then a replay log is not present */
0a122b
+    if (guid_eq(hdr->log_guid, zero_guid)) {
0a122b
+        goto exit;
0a122b
+    }
0a122b
+
0a122b
+    if (hdr->log_length == 0) {
0a122b
+        goto exit;
0a122b
+    }
0a122b
+
0a122b
+    if (hdr->log_length % VHDX_LOG_MIN_SIZE) {
0a122b
+        ret = -EINVAL;
0a122b
+        goto exit;
0a122b
+    }
0a122b
+
0a122b
+
0a122b
+    /* The log is present, we need to find if and where there is an active
0a122b
+     * sequence of valid entries present in the log.  */
0a122b
+
0a122b
+    ret = vhdx_log_search(bs, s, &logs);
0a122b
+    if (ret < 0) {
0a122b
+        goto exit;
0a122b
+    }
0a122b
+
0a122b
+    if (logs.valid) {
0a122b
+        /* now flush the log */
0a122b
+        ret = vhdx_log_flush(bs, s, &logs);
0a122b
+        if (ret < 0) {
0a122b
+            goto exit;
0a122b
+        }
0a122b
+        *flushed = true;
0a122b
+    }
0a122b
+
0a122b
+
0a122b
+exit:
0a122b
+    return ret;
0a122b
+}
0a122b
+
0a122b
+
0a122b
diff --git a/block/vhdx.c b/block/vhdx.c
0a122b
index 7d697e4..b552dde 100644
0a122b
--- a/block/vhdx.c
0a122b
+++ b/block/vhdx.c
0a122b
@@ -735,58 +735,22 @@ exit:
0a122b
     return ret;
0a122b
 }
0a122b
 
0a122b
-/* Parse the replay log.  Per the VHDX spec, if the log is present
0a122b
- * it must be replayed prior to opening the file, even read-only.
0a122b
- *
0a122b
- * If read-only, we must replay the log in RAM (or refuse to open
0a122b
- * a dirty VHDX file read-only */
0a122b
-static int vhdx_parse_log(BlockDriverState *bs, BDRVVHDXState *s)
0a122b
-{
0a122b
-    int ret = 0;
0a122b
-    int i;
0a122b
-    VHDXHeader *hdr;
0a122b
-
0a122b
-    hdr = s->headers[s->curr_header];
0a122b
-
0a122b
-    /* either the log guid, or log length is zero,
0a122b
-     * then a replay log is present */
0a122b
-    for (i = 0; i < sizeof(hdr->log_guid.data4); i++) {
0a122b
-        ret |= hdr->log_guid.data4[i];
0a122b
-    }
0a122b
-    if (hdr->log_guid.data1 == 0 &&
0a122b
-        hdr->log_guid.data2 == 0 &&
0a122b
-        hdr->log_guid.data3 == 0 &&
0a122b
-        ret == 0) {
0a122b
-        goto exit;
0a122b
-    }
0a122b
-
0a122b
-    /* per spec, only log version of 0 is supported */
0a122b
-    if (hdr->log_version != 0) {
0a122b
-        ret = -EINVAL;
0a122b
-        goto exit;
0a122b
-    }
0a122b
-
0a122b
-    if (hdr->log_length == 0) {
0a122b
-        goto exit;
0a122b
-    }
0a122b
-
0a122b
-    /* We currently do not support images with logs to replay */
0a122b
-    ret = -ENOTSUP;
0a122b
-
0a122b
-exit:
0a122b
-    return ret;
0a122b
-}
0a122b
-
0a122b
 
0a122b
 static void vhdx_close(BlockDriverState *bs)
0a122b
 {
0a122b
     BDRVVHDXState *s = bs->opaque;
0a122b
     qemu_vfree(s->headers[0]);
0a122b
+    s->headers[0] = NULL;
0a122b
     qemu_vfree(s->headers[1]);
0a122b
+    s->headers[1] = NULL;
0a122b
     qemu_vfree(s->bat);
0a122b
+    s->bat = NULL;
0a122b
     qemu_vfree(s->parent_entries);
0a122b
+    s->parent_entries = NULL;
0a122b
     migrate_del_blocker(s->migration_blocker);
0a122b
     error_free(s->migration_blocker);
0a122b
+    qemu_vfree(s->log.hdr);
0a122b
+    s->log.hdr = NULL;
0a122b
 }
0a122b
 
0a122b
 static int vhdx_open(BlockDriverState *bs, QDict *options, int flags,
0a122b
@@ -797,6 +761,7 @@ static int vhdx_open(BlockDriverState *bs, QDict *options, int flags,
0a122b
     uint32_t i;
0a122b
     uint64_t signature;
0a122b
     uint32_t data_blocks_cnt, bitmap_blocks_cnt;
0a122b
+    bool log_flushed = false;
0a122b
 
0a122b
 
0a122b
     s->bat = NULL;
0a122b
@@ -820,24 +785,25 @@ static int vhdx_open(BlockDriverState *bs, QDict *options, int flags,
0a122b
     vhdx_guid_generate(&s->session_guid);
0a122b
 
0a122b
     ret = vhdx_parse_header(bs, s);
0a122b
-    if (ret) {
0a122b
+    if (ret < 0) {
0a122b
         goto fail;
0a122b
     }
0a122b
 
0a122b
-    ret = vhdx_parse_log(bs, s);
0a122b
-    if (ret) {
0a122b
+    ret = vhdx_parse_log(bs, s, &log_flushed);
0a122b
+    if (ret < 0) {
0a122b
         goto fail;
0a122b
     }
0a122b
 
0a122b
     ret = vhdx_open_region_tables(bs, s);
0a122b
-    if (ret) {
0a122b
+    if (ret < 0) {
0a122b
         goto fail;
0a122b
     }
0a122b
 
0a122b
     ret = vhdx_parse_metadata(bs, s);
0a122b
-    if (ret) {
0a122b
+    if (ret < 0) {
0a122b
         goto fail;
0a122b
     }
0a122b
+
0a122b
     s->block_size = s->params.block_size;
0a122b
 
0a122b
     /* the VHDX spec dictates that virtual_disk_size is always a multiple of
0a122b
@@ -897,10 +863,7 @@ static int vhdx_open(BlockDriverState *bs, QDict *options, int flags,
0a122b
 
0a122b
     return 0;
0a122b
 fail:
0a122b
-    qemu_vfree(s->headers[0]);
0a122b
-    qemu_vfree(s->headers[1]);
0a122b
-    qemu_vfree(s->bat);
0a122b
-    qemu_vfree(s->parent_entries);
0a122b
+    vhdx_close(bs);
0a122b
     return ret;
0a122b
 }
0a122b
 
0a122b
diff --git a/block/vhdx.h b/block/vhdx.h
0a122b
index 81785e5..b150ad1 100644
0a122b
--- a/block/vhdx.h
0a122b
+++ b/block/vhdx.h
0a122b
@@ -326,7 +326,11 @@ typedef struct VHDXMetadataEntries {
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 typedef struct VHDXLogEntries {
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     uint64_t offset;
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     uint64_t length;
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-    uint32_t head;
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+    uint32_t write;
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+    uint32_t read;
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+    VHDXLogEntryHeader *hdr;
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+    void *desc_buffer;
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+    uint64_t sequence;
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     uint32_t tail;
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 } VHDXLogEntries;
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@@ -383,6 +387,7 @@ uint32_t vhdx_checksum_calc(uint32_t crc, uint8_t *buf, size_t size,
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 bool vhdx_checksum_is_valid(uint8_t *buf, size_t size, int crc_offset);
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+int vhdx_parse_log(BlockDriverState *bs, BDRVVHDXState *s, bool *flushed);
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 static inline void leguid_to_cpus(MSGUID *guid)
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 {
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-- 
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1.7.1
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