From 989d971046a36afa7acb67855f565603297ad2e8 Mon Sep 17 00:00:00 2001

From: Jeffrey Cody <jcody@redhat.com>

Date: Wed, 20 Nov 2013 19:44:01 +0100

Subject: [PATCH 18/25] block: vhdx - remove BAT file offset bit shifting

RH-Author: Jeffrey Cody <jcody@redhat.com>

Message-id: <348f6a1952aa68e9a5cfefb56a7e86f5ff1d01c9.1384975172.git.jcody@redhat.com>

Patchwork-id: 55811

O-Subject: [RHEL7 qemu-kvm PATCH 18/26] block: vhdx - remove BAT file offset bit shifting

Bugzilla: 879234

RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>

RH-Acked-by: Fam Zheng <famz@redhat.com>

Bit shifting can be fun, but in this case it was unnecessary.  The

upper 44 bits of the 64-bit BAT entry is specifies the File Offset,

so we shifted the bits to get access to the value.

However, per the spec the value is in MB.  So we dutifully shifted back

to the left by 20 bits, to convert to a true uint64_t file offset.

This replaces those steps with just a bit mask, to get rid of the lower

20 bits instead.

Signed-off-by: Jeff Cody <jcody@redhat.com>

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

(cherry picked from commit 0b7da092b40734538631c3ad461c1753a87535fc)

---

 block/vhdx.c | 6 ++----

 block/vhdx.h | 1 -

 2 files changed, 2 insertions(+), 5 deletions(-)

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>

---

 block/vhdx.c |    6 ++----

 block/vhdx.h |    1 -

 2 files changed, 2 insertions(+), 5 deletions(-)

diff --git a/block/vhdx.c b/block/vhdx.c

index baf8970..97099aa 100644

--- a/block/vhdx.c

+++ b/block/vhdx.c

@@ -985,7 +985,7 @@ static void vhdx_block_translate(BDRVVHDXState *s, int64_t sector_num,

     sinfo->bytes_avail = sinfo->sectors_avail << s->logical_sector_size_bits;

-    sinfo->file_offset = s->bat[sinfo->bat_idx] >> VHDX_BAT_FILE_OFF_BITS;

+    sinfo->file_offset = s->bat[sinfo->bat_idx] & VHDX_BAT_FILE_OFF_MASK;

     sinfo->block_offset = block_offset << s->logical_sector_size_bits;

@@ -999,7 +999,6 @@ static void vhdx_block_translate(BDRVVHDXState *s, int64_t sector_num,

      * in the block, and add in the payload data block offset

      * in the file, in bytes, to get the final read address */

-    sinfo->file_offset <<= 20;  /* now in bytes, rather than 1MB units */

     sinfo->file_offset += sinfo->block_offset;

 }

@@ -1110,8 +1109,7 @@ static void vhdx_update_bat_table_entry(BlockDriverState *bs, BDRVVHDXState *s,

 {

     /* The BAT entry is a uint64, with 44 bits for the file offset in units of

      * 1MB, and 3 bits for the block state. */

-    s->bat[sinfo->bat_idx]  = ((sinfo->file_offset>>20) <<

-                               VHDX_BAT_FILE_OFF_BITS);

+    s->bat[sinfo->bat_idx]  = sinfo->file_offset;

     s->bat[sinfo->bat_idx] |= state & VHDX_BAT_STATE_BIT_MASK;

diff --git a/block/vhdx.h b/block/vhdx.h

index a85c5c8..7deb7fd 100644

--- a/block/vhdx.h

+++ b/block/vhdx.h

@@ -229,7 +229,6 @@ typedef struct QEMU_PACKED VHDXLogDataSector {

 /* upper 44 bits are the file offset in 1MB units lower 3 bits are the state

    other bits are reserved */

 #define VHDX_BAT_STATE_BIT_MASK 0x07

-#define VHDX_BAT_FILE_OFF_BITS (64 - 44)

 #define VHDX_BAT_FILE_OFF_MASK  0xFFFFFFFFFFF00000 /* upper 44 bits */

 typedef uint64_t VHDXBatEntry;

-- 

1.7.1