[PATCH V15 04/14] block/export: track IOThread references

[Zhang Chen <zhangckid@gmail.com>]

Track the IOThreads used by a block export and identify the holder
with the unique BlockExportOptions id.

Acquire holder-aware references during export creation and release
them on error or export deletion.  Support both single- and
multi-iothread exports.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Zhang Chen <zhangckid@gmail.com>
---
 block/export/export.c  | 62 ++++++++++++++++++++++++++++++++++++------
 include/block/export.h |  5 ++++
 2 files changed, 58 insertions(+), 9 deletions(-)

diff --git a/block/export/export.c b/block/export/export.c
index b733f269f3..0e019545ef 100644
--- a/block/export/export.c
+++ b/block/export/export.c
@@ -15,7 +15,6 @@
 
 #include "block/block.h"
 #include "system/block-backend.h"
-#include "system/iothread.h"
 #include "block/export.h"
 #include "block/fuse.h"
 #include "block/nbd.h"
@@ -72,6 +71,32 @@ static const BlockExportDriver *blk_exp_find_driver(BlockExportType type)
     return NULL;
 }
 
+static void init_iothreads(const char *holder_id, IOThread **iothreads,
+                           size_t num_iothreads, AioContext **aio_ctxs)
+{
+    const IOThreadHolder holder = {
+        .type = IO_THREAD_HOLDER_KIND_BLOCK_EXPORT,
+        .u.block_export.export_id = (char *)holder_id,
+    };
+
+    for (size_t i = 0; i < num_iothreads; i++) {
+        aio_ctxs[i] = iothread_ref_and_get_aio_context(iothreads[i], &holder);
+    }
+}
+
+static void cleanup_iothreads(const char *holder_id, IOThread **iothreads,
+                              size_t num_iothreads)
+{
+    const IOThreadHolder holder = {
+        .type = IO_THREAD_HOLDER_KIND_BLOCK_EXPORT,
+        .u.block_export.export_id = (char *)holder_id,
+    };
+
+    for (size_t i = 0; i < num_iothreads; i++) {
+        iothread_unref_and_put_aio_context(iothreads[i], &holder);
+    }
+}
+
 BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
 {
     bool fixed_iothread = export->has_fixed_iothread && export->fixed_iothread;
@@ -85,6 +110,8 @@ BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
     AioContext *ctx;
     AioContext **multithread_ctxs = NULL;
     size_t multithread_count = 0;
+    g_autofree IOThread **local_iothreads = NULL;
+    size_t iothread_count = 0;
     uint64_t perm;
     int ret;
 
@@ -139,7 +166,10 @@ BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
             goto fail;
         }
 
-        new_ctx = iothread_get_aio_context(iothread);
+        local_iothreads = g_new0(IOThread *, 1);
+        local_iothreads[0] = iothread;
+        init_iothreads(export->id, local_iothreads, 1, &new_ctx);
+        iothread_count = 1;
 
         /* Ignore errors with fixed-iothread=false */
         set_context_errp = fixed_iothread ? errp : NULL;
@@ -163,8 +193,10 @@ BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
             return NULL;
         }
 
+        local_iothreads = g_new0(IOThread *, multithread_count);
         multithread_ctxs = g_new(AioContext *, multithread_count);
         i = 0;
+
         for (strList *e = iothread_list; e; e = e->next) {
             IOThread *iothread = iothread_by_id(e->value);
 
@@ -172,9 +204,12 @@ BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
                 error_setg(errp, "iothread \"%s\" not found", e->value);
                 goto fail;
             }
-            multithread_ctxs[i++] = iothread_get_aio_context(iothread);
+            local_iothreads[i++] = iothread;
         }
         assert(i == multithread_count);
+        init_iothreads(export->id, local_iothreads, multithread_count,
+                       multithread_ctxs);
+        iothread_count = multithread_count;
     }
 
     bdrv_graph_rdlock_main_loop();
@@ -225,12 +260,14 @@ BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
     assert(drv->instance_size >= sizeof(BlockExport));
     exp = g_malloc0(drv->instance_size);
     *exp = (BlockExport) {
-        .drv        = drv,
-        .refcount   = 1,
-        .user_owned = true,
-        .id         = g_strdup(export->id),
-        .ctx        = ctx,
-        .blk        = blk,
+        .drv                  = drv,
+        .refcount             = 1,
+        .user_owned           = true,
+        .id                   = g_strdup(export->id),
+        .ctx                  = ctx,
+        .blk                  = blk,
+        .iothreads            = g_steal_pointer(&local_iothreads),
+        .iothread_count       = iothread_count,
     };
 
     ret = drv->create(exp, export, multithread_ctxs, multithread_count, errp);
@@ -250,8 +287,12 @@ fail:
         blk_unref(blk);
     }
     if (exp) {
+        cleanup_iothreads(exp->id, exp->iothreads, exp->iothread_count);
+        g_free(exp->iothreads);
         g_free(exp->id);
         g_free(exp);
+    } else {
+        cleanup_iothreads(export->id, local_iothreads, iothread_count);
     }
     g_free(multithread_ctxs);
     return NULL;
@@ -273,6 +314,9 @@ static void blk_exp_delete_bh(void *opaque)
     exp->drv->delete(exp);
     blk_set_dev_ops(exp->blk, NULL, NULL);
     blk_unref(exp->blk);
+
+    cleanup_iothreads(exp->id, exp->iothreads, exp->iothread_count);
+    g_free(exp->iothreads);
     qapi_event_send_block_export_deleted(exp->id);
     g_free(exp->id);
     g_free(exp);
diff --git a/include/block/export.h b/include/block/export.h
index ca45da928c..ce8e4eb604 100644
--- a/include/block/export.h
+++ b/include/block/export.h
@@ -16,6 +16,7 @@
 
 #include "qapi/qapi-types-block-export.h"
 #include "qemu/queue.h"
+#include "system/iothread.h"
 
 typedef struct BlockExport BlockExport;
 
@@ -89,6 +90,10 @@ struct BlockExport {
 
     /* List entry for block_exports */
     QLIST_ENTRY(BlockExport) next;
+
+    /* The IOThreads utilized by this specific block export */
+    IOThread **iothreads;
+    size_t iothread_count;
 };
 
 BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp);
-- 
2.43.0