[Qemu-devel] [PATCH 02/10] block: add .bdrv_co_is_allocated()

[Stefan Hajnoczi]

This patch adds the .bdrv_co_is_allocated() interface which is identical
to .bdrv_is_allocated() but runs in coroutine context.  Running in
coroutine context implies that other coroutines might be performing I/O
at the same time.   Therefore it must be safe to run while the following
BlockDriver functions are in-flight:

    .bdrv_co_readv()
    .bdrv_co_writev()
    .bdrv_co_flush()
    .bdrv_co_is_allocated()

The new .bdrv_co_is_allocated() interface is useful because it can be
used when a VM is running, whereas .bdrv_is_allocated() is a synchronous
interface that does not cope with parallel requests.

Signed-off-by: Stefan Hajnoczi <stefa...@linux.vnet.ibm.com>
---
 block.c     |   37 +++++++++++++++++++++++++++++++++++++
 block_int.h |    2 ++
 2 files changed, 39 insertions(+), 0 deletions(-)

diff --git a/block.c b/block.c
index e6ac6d3..f8705b7 100644
--- a/block.c
+++ b/block.c
@@ -1771,6 +1771,26 @@ int bdrv_has_zero_init(BlockDriverState *bs)
     return 1;
 }
 
+typedef struct BdrvCoIsAllocatedData {
+    BlockDriverState *bs;
+    int64_t sector_num;
+    int nb_sectors;
+    int *pnum;
+    int ret;
+    bool done;
+} BdrvCoIsAllocatedData;
+
+/* Coroutine wrapper for bdrv_is_allocated() */
+static void coroutine_fn bdrv_is_allocated_co_entry(void *opaque)
+{
+    BdrvCoIsAllocatedData *data = opaque;
+    BlockDriverState *bs = data->bs;
+
+    data->ret = bs->drv->bdrv_co_is_allocated(bs, data->sector_num,
+                                              data->nb_sectors, data->pnum);
+    data->done = true;
+}
+
 /*
  * Returns true iff the specified sector is present in the disk image. Drivers
  * not implementing the functionality are assumed to not support backing files,
@@ -1786,6 +1806,23 @@ int bdrv_is_allocated(BlockDriverState *bs, int64_t 
sector_num, int nb_sectors,
        int *pnum)
 {
     int64_t n;
+    if (bs->drv->bdrv_co_is_allocated) {
+        Coroutine *co;
+        BdrvCoIsAllocatedData data = {
+            .bs = bs,
+            .sector_num = sector_num,
+            .nb_sectors = nb_sectors,
+            .pnum = pnum,
+            .done = false,
+        };
+
+        co = qemu_coroutine_create(bdrv_is_allocated_co_entry);
+        qemu_coroutine_enter(co, &data);
+        while (!data.done) {
+            qemu_aio_wait();
+        }
+        return data.ret;
+    }
     if (!bs->drv->bdrv_is_allocated) {
         if (sector_num >= bs->total_sectors) {
             *pnum = 0;
diff --git a/block_int.h b/block_int.h
index f4547f6..1c1351c 100644
--- a/block_int.h
+++ b/block_int.h
@@ -87,6 +87,8 @@ struct BlockDriver {
     int coroutine_fn (*bdrv_co_flush)(BlockDriverState *bs);
     int coroutine_fn (*bdrv_co_discard)(BlockDriverState *bs,
         int64_t sector_num, int nb_sectors);
+    int coroutine_fn (*bdrv_co_is_allocated)(BlockDriverState *bs,
+        int64_t sector_num, int nb_sectors, int *pnum);
 
     int (*bdrv_aio_multiwrite)(BlockDriverState *bs, BlockRequest *reqs,
         int num_reqs);
-- 
1.7.7.1