block: define get_block_status return value

Define the return value of get_block_status.  Bits 0, 1, 2 and 9-62
are valid; bit 63 (the sign bit) is reserved for errors.  Bits 3-8
are left for future extensions.

The return code is compatible with the old is_allocated API: if a driver
only returns 0 or 1 (aka BDRV_BLOCK_DATA) like is_allocated used to,
clients of is_allocated will not have any change in behavior.  Still,
we will return more precise information in the next patches and the
new definition of bdrv_is_allocated is already prepared for this.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

2 files changed, 34 insertions, 2 deletions

diff --git a/block.c b/block.c
index a5bfe74ef6..97406ec7bd 100644
--- a/block.c
+++ b/block.c
@@ -3093,7 +3093,7 @@ static int64_t coroutine_fn bdrv_co_get_block_status(BlockDriverState *bs,
 
     if (!bs->drv->bdrv_co_get_block_status) {
         *pnum = nb_sectors;
-        return 1;
+        return BDRV_BLOCK_DATA;
     }
 
     return bs->drv->bdrv_co_get_block_status(bs, sector_num, nb_sectors, pnum);
@@ -3143,7 +3143,13 @@ int64_t bdrv_get_block_status(BlockDriverState *bs, int64_t sector_num,
 int coroutine_fn bdrv_is_allocated(BlockDriverState *bs, int64_t sector_num,
                                    int nb_sectors, int *pnum)
 {
-    return bdrv_get_block_status(bs, sector_num, nb_sectors, pnum);
+    int64_t ret = bdrv_get_block_status(bs, sector_num, nb_sectors, pnum);
+    if (ret < 0) {
+        return ret;
+    }
+    return
+        (ret & BDRV_BLOCK_DATA) ||
+        ((ret & BDRV_BLOCK_ZERO) && !bdrv_has_zero_init(bs));
 }
 
 /*
diff --git a/include/block/block.h b/include/block/block.h
index 0b83321419..728ec1aebf 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -81,6 +81,32 @@ typedef struct BlockDevOps {
 #define BDRV_SECTOR_SIZE   (1ULL << BDRV_SECTOR_BITS)
 #define BDRV_SECTOR_MASK   ~(BDRV_SECTOR_SIZE - 1)
 
+/* BDRV_BLOCK_DATA: data is read from bs->file or another file
+ * BDRV_BLOCK_ZERO: sectors read as zero
+ * BDRV_BLOCK_OFFSET_VALID: sector stored in bs->file as raw data
+ *
+ * If BDRV_BLOCK_OFFSET_VALID is set, bits 9-62 represent the offset in
+ * bs->file where sector data can be read from as raw data.
+ *
+ * DATA == 0 && ZERO == 0 means that data is read from backing_hd if present.
+ *
+ * DATA ZERO OFFSET_VALID
+ *  t    t        t       sectors read as zero, bs->file is zero at offset
+ *  t    f        t       sectors read as valid from bs->file at offset
+ *  f    t        t       sectors preallocated, read as zero, bs->file not
+ *                        necessarily zero at offset
+ *  f    f        t       sectors preallocated but read from backing_hd,
+ *                        bs->file contains garbage at offset
+ *  t    t        f       sectors preallocated, read as zero, unknown offset
+ *  t    f        f       sectors read from unknown file or offset
+ *  f    t        f       not allocated or unknown offset, read as zero
+ *  f    f        f       not allocated or unknown offset, read from backing_hd
+ */
+#define BDRV_BLOCK_DATA         1
+#define BDRV_BLOCK_ZERO         2
+#define BDRV_BLOCK_OFFSET_VALID 4
+#define BDRV_BLOCK_OFFSET_MASK  BDRV_SECTOR_MASK
+
 typedef enum {
     BDRV_ACTION_REPORT, BDRV_ACTION_IGNORE, BDRV_ACTION_STOP
 } BlockErrorAction;