From 0b7da092b40734538631c3ad461c1753a87535fc Mon Sep 17 00:00:00 2001 From: Jeff Cody Date: Wed, 30 Oct 2013 10:44:49 -0400 Subject: block: vhdx - remove BAT file offset bit shifting 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 Signed-off-by: Stefan Hajnoczi --- 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 050f0719c8..158edab7b0 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; } @@ -1098,8 +1097,7 @@ 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 f3315480ea..d3598e0a27 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; -- cgit v1.2.3