qcow2 format: keep 'num_free_bytes', and show it upon 'info blockstats' (Uri Lublin)

'num_free_bytes' is the number of non-allocated bytes below highest-allocation.
It's useful, together with the highest-allocation, to figure out how
fragmented the image is, and how likely it will run out-of-space soon.

For example when the highest allocation is high (almost end-of-disk), but 
many bytes (clusters) are free, and can be re-allocated when neeeded, than
we know it's probably not going to reach end-of-disk-space soon.

Added bookkeeping to block-qcow2.c
Export it using BlockDeviceInfo
Show it upon 'info blockstats' if BlockDeviceInfo exists

Signed-off-by: Uri Lublin <uril@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>


git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6407 c046a42c-6fe2-441c-8c8c-71466251a162

block-qcow2.c

@@ -145,6 +145,7 @@ typedef struct BDRVQcowState {
     AES_KEY aes_decrypt_key;
 
     int64_t highest_alloc; /* highest cluester allocated (in clusters) */
+    int64_t nc_free;       /* num of free clusters below highest_alloc */
 
     uint64_t snapshots_offset;
     int snapshots_size;
@@ -173,7 +174,7 @@ static void free_clusters(BlockDriverState *bs,
 #ifdef DEBUG_ALLOC
 static void check_refcounts(BlockDriverState *bs);
 #endif
-static void scan_refcount(BlockDriverState *bs, int64_t *high);
+static void scan_refcount(BlockDriverState *bs, int64_t *high, int64_t *free);
 
 
 static int qcow_probe(const uint8_t *buf, int buf_size, const char *filename)
@@ -283,7 +284,7 @@ static int qcow_open(BlockDriverState *bs, const char *filename, int flags)
     if (refcount_init(bs) < 0)
         goto fail;
 
-    scan_refcount(bs, &s->highest_alloc);
+    scan_refcount(bs, &s->highest_alloc, &s->nc_free);
 
     /* read the backing file name */
     if (header.backing_file_offset != 0) {
@@ -1672,6 +1673,7 @@ static int qcow_get_info(BlockDriverState *bs, BlockDriverInfo *bdi)
     bdi->vm_state_offset = (int64_t)s->l1_vm_state_index <<
         (s->cluster_bits + s->l2_bits);
     bdi->highest_alloc = s->highest_alloc << s->cluster_bits;
+    bdi->num_free_bytes = s->nc_free  << s->cluster_bits;
     return 0;
 }
 
@@ -2214,25 +2216,35 @@ static int load_refcount_block(BlockDriverState *bs,
     return 0;
 }
 
-static void scan_refcount(BlockDriverState *bs, int64_t *high)
+static void scan_refcount(BlockDriverState *bs, int64_t *high, int64_t *free)
 {
     BDRVQcowState *s = bs->opaque;
-    int64_t refcnt_index, cluster_index, cluster_end, h = 0;
+    int64_t refcnt_index, cluster_index, cluster_end, h = 0, f = 0;
+    int64_t tail = 0; /* do not count last consecutive free entries */
 
     for (refcnt_index=0; refcnt_index < s->refcount_table_size; refcnt_index++){
         if (s->refcount_table[refcnt_index] == 0) {
+            f += 1 << (s->cluster_bits - REFCOUNT_SHIFT);
+            tail += 1 << (s->cluster_bits - REFCOUNT_SHIFT);
             continue;
         }
         cluster_index = refcnt_index << (s->cluster_bits - REFCOUNT_SHIFT);
         cluster_end = (refcnt_index + 1) << (s->cluster_bits - REFCOUNT_SHIFT);
         for ( ; cluster_index < cluster_end; cluster_index++) {
-            if (get_refcount(bs, cluster_index) == 0)
-                /* do nothing -- reserved for free counting */;
-            else
+            if (get_refcount(bs, cluster_index) == 0) {
+                f++;
+                tail++;
+            }
+            else {
                 h = cluster_index;
+                tail = 0;
+            }
         }
     }
 
+    f -= tail;
+    if (free)
+        *free = f;
     if (high)
         *high = (h+1);
 }
@@ -2278,8 +2290,10 @@ retry:
             (s->free_cluster_index - nb_clusters) << s->cluster_bits);
 #endif
 
-    if (s->highest_alloc < s->free_cluster_index)
+    if (s->highest_alloc < s->free_cluster_index) {
+        s->nc_free += (s->free_cluster_index - s->highest_alloc);
         s->highest_alloc = s->free_cluster_index;
+    }
 
     return (s->free_cluster_index - nb_clusters) << s->cluster_bits;
 }
@@ -2456,6 +2470,12 @@ static int update_cluster_refcount(BlockDriverState *bs,
     block_index = cluster_index &
         ((1 << (s->cluster_bits - REFCOUNT_SHIFT)) - 1);
     refcount = be16_to_cpu(s->refcount_block_cache[block_index]);
+
+    if (refcount == 1 && addend == -1)
+        s->nc_free += 1;
+    else if (refcount == 0 && addend == 1)
+        s->nc_free -= 1;
+
     refcount += addend;
     if (refcount < 0 || refcount > 0xffff)
         return -EINVAL;

block.c

@@ -1090,8 +1090,9 @@ void bdrv_info_stats (void)
 		     bs->rd_bytes, bs->wr_bytes,
 		     bs->rd_ops, bs->wr_ops);
         if (bdrv_get_info(bs, &bdi) == 0)
-            term_printf(" high=%" PRIu64,
-                        bdi.highest_alloc);
+            term_printf(" high=%" PRId64
+                        " bytes_free=%" PRId64,
+                        bdi.highest_alloc, bdi.num_free_bytes);
         term_printf("\n");
     }
 }

block.h

@@ -27,6 +27,7 @@ typedef struct BlockDriverInfo {
     /* offset at which the VM state can be saved (0 if not possible) */
     int64_t vm_state_offset;
     int64_t highest_alloc; /* highest allocated block offset (in bytes) */
+    int64_t num_free_bytes; /* below highest_alloc  */
 } BlockDriverInfo;
 
 typedef struct QEMUSnapshotInfo {