[RFC PATCH 4/7] block-backend: add I/O hang drain when disbale

[Ying Fang]

To disable I/O hang, all hanging AIOs need to be drained. A rehandle status
field is introduced to notify rehandle mechanism not to rehandle failed AIOs
when I/O hang is disabled.

Signed-off-by: Ying Fang <fangying1@huawei.com>
Signed-off-by: Jiahui Cen <cenjiahui@huawei.com>
---
 block/block-backend.c          | 85 ++++++++++++++++++++++++++++++++--
 include/sysemu/block-backend.h |  3 ++
 2 files changed, 84 insertions(+), 4 deletions(-)

diff --git a/block/block-backend.c b/block/block-backend.c
index d0b2b59f55..95b2d6a679 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -37,6 +37,9 @@ static AioContext *blk_aiocb_get_aio_context(BlockAIOCB *acb);
 
 /* block backend rehandle timer interval 5s */
 #define BLOCK_BACKEND_REHANDLE_TIMER_INTERVAL   5000
+#define BLOCK_BACKEND_REHANDLE_NORMAL           1
+#define BLOCK_BACKEND_REHANDLE_DRAIN_REQUESTED  2
+#define BLOCK_BACKEND_REHANDLE_DRAINED          3
 
 enum BlockIOHangStatus {
     BLOCK_IO_HANG_STATUS_NORMAL = 0,
@@ -50,6 +53,8 @@ typedef struct BlockBackendRehandleInfo {
 
     unsigned int in_flight;
     QTAILQ_HEAD(, BlkAioEmAIOCB) re_aios;
+
+    int status;
 } BlockBackendRehandleInfo;
 
 typedef struct BlockBackendAioNotifier {
@@ -471,6 +476,8 @@ static void blk_delete(BlockBackend *blk)
     assert(!blk->refcnt);
     assert(!blk->name);
     assert(!blk->dev);
+    assert(atomic_read(&blk->reinfo.in_flight) == 0);
+    blk_rehandle_disable(blk);
     if (blk->public.throttle_group_member.throttle_state) {
         blk_io_limits_disable(blk);
     }
@@ -2460,6 +2467,37 @@ static void blk_rehandle_remove_aiocb(BlockBackend *blk, 
BlkAioEmAIOCB *acb)
     atomic_dec(&blk->reinfo.in_flight);
 }
 
+static void blk_rehandle_drain(BlockBackend *blk)
+{
+    if (blk_bs(blk)) {
+        bdrv_drained_begin(blk_bs(blk));
+        BDRV_POLL_WHILE(blk_bs(blk), atomic_read(&blk->reinfo.in_flight) > 0);
+        bdrv_drained_end(blk_bs(blk));
+    }
+}
+
+static bool blk_rehandle_is_paused(BlockBackend *blk)
+{
+    return blk->reinfo.status == BLOCK_BACKEND_REHANDLE_DRAIN_REQUESTED ||
+           blk->reinfo.status == BLOCK_BACKEND_REHANDLE_DRAINED;
+}
+
+static void blk_rehandle_pause(BlockBackend *blk)
+{
+    BlockBackendRehandleInfo *reinfo = &blk->reinfo;
+
+    aio_context_acquire(blk_get_aio_context(blk));
+    if (!reinfo->enable || reinfo->status == BLOCK_BACKEND_REHANDLE_DRAINED) {
+        aio_context_release(blk_get_aio_context(blk));
+        return;
+    }
+
+    reinfo->status = BLOCK_BACKEND_REHANDLE_DRAIN_REQUESTED;
+    blk_rehandle_drain(blk);
+    reinfo->status = BLOCK_BACKEND_REHANDLE_DRAINED;
+    aio_context_release(blk_get_aio_context(blk));
+}
+
 static void blk_rehandle_timer_cb(void *opaque)
 {
     BlockBackend *blk = opaque;
@@ -2559,10 +2597,12 @@ static void blk_rehandle_aio_complete(BlkAioEmAIOCB 
*acb)
 
     if (acb->has_returned) {
         blk_dec_in_flight(acb->rwco.blk);
-        need_rehandle = blk_rehandle_aio(acb, &has_timeout);
-        if (need_rehandle) {
-            blk_rehandle_insert_aiocb(acb->rwco.blk, acb);
-            return;
+        if (!blk_rehandle_is_paused(acb->rwco.blk)) {
+            need_rehandle = blk_rehandle_aio(acb, &has_timeout);
+            if (need_rehandle) {
+                blk_rehandle_insert_aiocb(acb->rwco.blk, acb);
+                return;
+            }
         }
 
         acb->common.cb(acb->common.opaque, acb->rwco.ret);
@@ -2576,6 +2616,42 @@ static void blk_rehandle_aio_complete(BlkAioEmAIOCB *acb)
     }
 }
 
+void blk_rehandle_enable(BlockBackend *blk)
+{
+    BlockBackendRehandleInfo *reinfo = &blk->reinfo;
+
+    aio_context_acquire(blk_get_aio_context(blk));
+    if (reinfo->enable) {
+        aio_context_release(blk_get_aio_context(blk));
+        return;
+    }
+
+    reinfo->ts = aio_timer_new(blk_get_aio_context(blk), QEMU_CLOCK_REALTIME,
+                               SCALE_MS, blk_rehandle_timer_cb, blk);
+    reinfo->timer_interval_ms = BLOCK_BACKEND_REHANDLE_TIMER_INTERVAL;
+    reinfo->status = BLOCK_BACKEND_REHANDLE_NORMAL;
+    reinfo->enable = true;
+    aio_context_release(blk_get_aio_context(blk));
+}
+
+void blk_rehandle_disable(BlockBackend *blk)
+{
+    if (!blk->reinfo.enable) {
+        return;
+    }
+
+    blk_rehandle_pause(blk);
+    timer_del(blk->reinfo.ts);
+    timer_free(blk->reinfo.ts);
+    blk->reinfo.ts = NULL;
+    blk->reinfo.enable = false;
+}
+
+bool blk_iohang_is_enabled(BlockBackend *blk)
+{
+    return blk->iohang_timeout != 0;
+}
+
 void blk_iohang_init(BlockBackend *blk, int64_t iohang_timeout)
 {
     if (!blk) {
@@ -2588,6 +2664,7 @@ void blk_iohang_init(BlockBackend *blk, int64_t 
iohang_timeout)
     blk->iohang_status = BLOCK_IO_HANG_STATUS_NORMAL;
     if (iohang_timeout > 0) {
         blk->iohang_timeout = iohang_timeout;
+        blk_rehandle_enable(blk);
     }
 }
 
diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
index bfebe3a960..375ae13b0b 100644
--- a/include/sysemu/block-backend.h
+++ b/include/sysemu/block-backend.h
@@ -268,6 +268,9 @@ const BdrvChild *blk_root(BlockBackend *blk);
 
 int blk_make_empty(BlockBackend *blk, Error **errp);
 
+void blk_rehandle_enable(BlockBackend *blk);
+void blk_rehandle_disable(BlockBackend *blk);
+bool blk_iohang_is_enabled(BlockBackend *blk);
 void blk_iohang_init(BlockBackend *blk, int64_t iohang_timeout);
 
 #endif
-- 
2.23.0