file-posix: account discard operations

This will help to identify how many of the user-issued discard operations
(accounted on a device level) have actually suceeded down on the host file
(even though the numbers will not be exactly the same if non-raw format
driver is used (e.g. qcow2 sending metadata discards)).

Note that these numbers will not include discards triggered by
write-zeroes + MAY_UNMAP calls.

Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-id: 20190923121737.83281-9-anton.nefedov@virtuozzo.com
Signed-off-by: Max Reitz <mreitz@redhat.com>

block/file-posix.c

@@ -161,6 +161,11 @@ typedef struct BDRVRawState {
     bool needs_alignment;
     bool drop_cache;
     bool check_cache_dropped;
+    struct {
+        uint64_t discard_nb_ok;
+        uint64_t discard_nb_failed;
+        uint64_t discard_bytes_ok;
+    } stats;
 
     PRManager *pr_mgr;
 } BDRVRawState;
@@ -2660,11 +2665,22 @@ static void coroutine_fn raw_co_invalidate_cache(BlockDriverState *bs,
 #endif /* !__linux__ */
 }
 
+static void raw_account_discard(BDRVRawState *s, uint64_t nbytes, int ret)
+{
+    if (ret) {
+        s->stats.discard_nb_failed++;
+    } else {
+        s->stats.discard_nb_ok++;
+        s->stats.discard_bytes_ok += nbytes;
+    }
+}
+
 static coroutine_fn int
 raw_do_pdiscard(BlockDriverState *bs, int64_t offset, int bytes, bool blkdev)
 {
     BDRVRawState *s = bs->opaque;
     RawPosixAIOData acb;
+    int ret;
 
     acb = (RawPosixAIOData) {
         .bs             = bs,
@@ -2678,7 +2694,9 @@ raw_do_pdiscard(BlockDriverState *bs, int64_t offset, int bytes, bool blkdev)
         acb.aio_type |= QEMU_AIO_BLKDEV;
     }
 
-    return raw_thread_pool_submit(bs, handle_aiocb_discard, &acb);
+    ret = raw_thread_pool_submit(bs, handle_aiocb_discard, &acb);
+    raw_account_discard(s, bytes, ret);
+    return ret;
 }
 
 static coroutine_fn int
@@ -3301,10 +3319,12 @@ static int fd_open(BlockDriverState *bs)
 static coroutine_fn int
 hdev_co_pdiscard(BlockDriverState *bs, int64_t offset, int bytes)
 {
+    BDRVRawState *s = bs->opaque;
     int ret;
 
     ret = fd_open(bs);
     if (ret < 0) {
+        raw_account_discard(s, bytes, ret);
         return ret;
     }
     return raw_do_pdiscard(bs, offset, bytes, true);