block: Remove wr_highest_sector from BlockAcctStats

BlockAcctStats contains statistics about the data transferred from and
to the device; wr_highest_sector does not fit in with the rest.

Furthermore, those statistics are supposed to be specific for a certain
device and not necessarily for a BDS (see the comment above
bdrv_get_stats()); on the other hand, wr_highest_sector may be a rather
important information to know for each BDS. When BlockAcctStats is
finally removed from the BDS, we will want to keep wr_highest_sector in
the BDS.

Finally, wr_highest_sector is renamed to wr_highest_offset and given the
appropriate meaning. Externally, it is represented as an offset so there
is no point in doing something different internally. Its definition is
changed to match that in qapi/block-core.json which is "the offset after
the greatest byte written to". Doing so should not cause any harm since
if external programs tried to calculate the volume usage by
(wr_highest_offset + 512) / volume_size, after this patch they will just
assume the volume to be full slightly earlier than before.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/accounting.c

@@ -47,14 +47,6 @@ void block_acct_done(BlockAcctStats *stats, BlockAcctCookie *cookie)
 }
 
 
-void block_acct_highest_sector(BlockAcctStats *stats, int64_t sector_num,
-                               unsigned int nb_sectors)
-{
-    if (stats->wr_highest_sector < sector_num + nb_sectors - 1) {
-        stats->wr_highest_sector = sector_num + nb_sectors - 1;
-    }
-}
-
 void block_acct_merge_done(BlockAcctStats *stats, enum BlockAcctType type,
                       int num_requests)
 {

block/io.c

@@ -1151,7 +1151,9 @@ static int coroutine_fn bdrv_aligned_pwritev(BlockDriverState *bs,
 
     bdrv_set_dirty(bs, sector_num, nb_sectors);
 
-    block_acct_highest_sector(&bs->stats, sector_num, nb_sectors);
+    if (bs->wr_highest_offset < offset + bytes) {
+        bs->wr_highest_offset = offset + bytes;
+    }
 
     if (ret >= 0) {
         bs->total_sectors = MAX(bs->total_sectors, sector_num + nb_sectors);

block/qapi.c

@@ -350,13 +350,13 @@ static BlockStats *bdrv_query_stats(const BlockDriverState *bs,
     s->stats->wr_operations = bs->stats.nr_ops[BLOCK_ACCT_WRITE];
     s->stats->rd_merged = bs->stats.merged[BLOCK_ACCT_READ];
     s->stats->wr_merged = bs->stats.merged[BLOCK_ACCT_WRITE];
-    s->stats->wr_highest_offset =
-        bs->stats.wr_highest_sector * BDRV_SECTOR_SIZE;
     s->stats->flush_operations = bs->stats.nr_ops[BLOCK_ACCT_FLUSH];
     s->stats->wr_total_time_ns = bs->stats.total_time_ns[BLOCK_ACCT_WRITE];
     s->stats->rd_total_time_ns = bs->stats.total_time_ns[BLOCK_ACCT_READ];
     s->stats->flush_total_time_ns = bs->stats.total_time_ns[BLOCK_ACCT_FLUSH];
 
+    s->stats->wr_highest_offset = bs->wr_highest_offset;
+
     if (bs->file) {
         s->has_parent = true;
         s->parent = bdrv_query_stats(bs->file->bs, query_backing);

include/block/accounting.h

@@ -40,7 +40,6 @@ typedef struct BlockAcctStats {
     uint64_t nr_ops[BLOCK_MAX_IOTYPE];
     uint64_t total_time_ns[BLOCK_MAX_IOTYPE];
     uint64_t merged[BLOCK_MAX_IOTYPE];
-    uint64_t wr_highest_sector;
 } BlockAcctStats;
 
 typedef struct BlockAcctCookie {
@@ -52,8 +51,6 @@ typedef struct BlockAcctCookie {
 void block_acct_start(BlockAcctStats *stats, BlockAcctCookie *cookie,
                       int64_t bytes, enum BlockAcctType type);
 void block_acct_done(BlockAcctStats *stats, BlockAcctCookie *cookie);
-void block_acct_highest_sector(BlockAcctStats *stats, int64_t sector_num,
-                               unsigned int nb_sectors);
 void block_acct_merge_done(BlockAcctStats *stats, enum BlockAcctType type,
                            int num_requests);
 

include/block/block_int.h

@@ -402,6 +402,9 @@ struct BlockDriverState {
     /* I/O stats (display with "info blockstats"). */
     BlockAcctStats stats;
 
+    /* Offset after the highest byte written to */
+    uint64_t wr_highest_offset;
+
     /* I/O Limits */
     BlockLimits bl;
 

qmp-commands.hx

@@ -2520,8 +2520,8 @@ Each json-object contain the following:
     - "wr_total_time_ns": total time spend on writes in nano-seconds (json-int)
     - "rd_total_time_ns": total time spend on reads in nano-seconds (json-int)
     - "flush_total_time_ns": total time spend on cache flushes in nano-seconds (json-int)
-    - "wr_highest_offset": Highest offset of a sector written since the
-                           BlockDriverState has been opened (json-int)
+    - "wr_highest_offset": The offset after the greatest byte written to the
+                           BlockDriverState since it has been opened (json-int)
     - "rd_merged": number of read requests that have been merged into
                    another request (json-int)
     - "wr_merged": number of write requests that have been merged into