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[v2,1/7] dmg: Introduce a new struct to cache random access points

Message ID 1493280397-9622-2-git-send-email-ashijeetacharya@gmail.com
State New
Headers show

Commit Message

Ashijeet Acharya April 27, 2017, 8:06 a.m. UTC 
We need to cache the random access point while performing partial
decompression so that we can resume decompression from that point
onwards in our next sequential read request. Introduce a new struct
DMGReadState which will help us do this.

Signed-off-by: Ashijeet Acharya <ashijeetacharya@gmail.com>
---
 block/dmg.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

Comments

Stefan Hajnoczi May 5, 2017, 1:12 p.m. UTC | #1 
On Thu, Apr 27, 2017 at 01:36:31PM +0530, Ashijeet Acharya wrote:
> @@ -51,6 +60,7 @@ typedef struct BDRVDMGState {
>      uint8_t *compressed_chunk;
>      uint8_t *uncompressed_chunk;
>      z_stream zstream;
> +    DMGReadState *drs;

This doesn't need to be a pointer.  The object is allocated in
.bdrv_open() and freed in .bdrv_close().  It's simpler to drop the heap
allocation and simply inline the struct:

    DMGReadState drs;
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Patch

diff --git a/block/dmg.h b/block/dmg.h
index b592d6f..ee67ae1 100644
--- a/block/dmg.h
+++ b/block/dmg.h
@@ -31,6 +31,15 @@ 
 #include "block/block_int.h"
 #include <zlib.h>
 
+/* used to cache current position in compressed input stream */
+typedef struct DMGReadState {
+    uint8_t *saved_next_in;
+    int64_t saved_avail_in;
+    int32_t saved_chunk_type;
+    int64_t sectors_read; /* possible sectors read in each cycle */
+    int32_t sector_offset_in_chunk;
+} DMGReadState;
+
 typedef struct BDRVDMGState {
     CoMutex lock;
     /* each chunk contains a certain number of sectors,
@@ -51,6 +60,7 @@  typedef struct BDRVDMGState {
     uint8_t *compressed_chunk;
     uint8_t *uncompressed_chunk;
     z_stream zstream;
+    DMGReadState *drs;
 } BDRVDMGState;
 
 extern int (*dmg_uncompress_bz2)(char *next_in, unsigned int avail_in,