[Qemu-devel] [PATCH v2 5/8] blockdev: Add list of monitor-owned BlockBackends

[Max Reitz <mreitz@redhat.com>]

The monitor does hold references to some BlockBackends so it should have
a list of those BBs; blk_backends is a different list, as it contains
references to all BBs (after a follow-up patch, that is), and that
should not be changed because we do need such a list.

monitor_remove_blk() is idempotent so that we can call it in
blockdev_auto_del() without having to care whether it had been called in
do_drive_del() before. monitor_add_blk() is idempotent for symmetry
reasons (monitor_remove_blk() is, so it would be strange for
monitor_add_blk() not to be).

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/block-backend.c          | 34 +++++++++++++++++++++++++++++++++-
 blockdev.c                     |  8 ++++++++
 include/sysemu/block-backend.h |  2 ++
 3 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/block/block-backend.c b/block/block-backend.c
index c89340e..e35d84f 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -29,6 +29,8 @@ struct BlockBackend {
     BlockDriverState *bs;
     DriveInfo *legacy_dinfo;    /* null unless created by drive_new() */
     QTAILQ_ENTRY(BlockBackend) link; /* for blk_backends */
+    QTAILQ_ENTRY(BlockBackend) monitor_link; /* for monitor_block_backends */
+    bool in_monitor_list;
 
     void *dev;                  /* attached device model, if any */
     /* TODO change to DeviceState when all users are qdevified */
@@ -70,6 +72,11 @@ static void drive_info_del(DriveInfo *dinfo);
 static QTAILQ_HEAD(, BlockBackend) blk_backends =
     QTAILQ_HEAD_INITIALIZER(blk_backends);
 
+/* All BlockBackends referenced by the monitor and which are iterated through by
+ * blk_next() */
+static QTAILQ_HEAD(, BlockBackend) monitor_block_backends =
+    QTAILQ_HEAD_INITIALIZER(monitor_block_backends);
+
 /*
  * Create a new BlockBackend with @name, with a reference count of one.
  * @name must not be null or empty.
@@ -248,7 +255,8 @@ void blk_remove_all_bs(void)
  */
 BlockBackend *blk_next(BlockBackend *blk)
 {
-    return blk ? QTAILQ_NEXT(blk, link) : QTAILQ_FIRST(&blk_backends);
+    return blk ? QTAILQ_NEXT(blk, monitor_link)
+               : QTAILQ_FIRST(&monitor_block_backends);
 }
 
 /*
@@ -267,6 +275,30 @@ BlockBackend *blk_next_inserted(BlockBackend *blk)
 }
 
 /*
+ * Add a BlockBackend into the list of backends referenced by the monitor.
+ * Strictly for use by blockdev.c.
+ */
+void monitor_add_blk(BlockBackend *blk)
+{
+    if (!blk->in_monitor_list) {
+        QTAILQ_INSERT_TAIL(&monitor_block_backends, blk, monitor_link);
+        blk->in_monitor_list = true;
+    }
+}
+
+/*
+ * Remove a BlockBackend from the list of backends referenced by the monitor.
+ * Strictly for use by blockdev.c.
+ */
+void monitor_remove_blk(BlockBackend *blk)
+{
+    if (blk->in_monitor_list) {
+        QTAILQ_REMOVE(&monitor_block_backends, blk, monitor_link);
+        blk->in_monitor_list = false;
+    }
+}
+
+/*
  * Return @blk's name, a non-null string.
  * Wart: the name is empty iff @blk has been hidden with
  * blk_hide_on_behalf_of_hmp_drive_del().
diff --git a/blockdev.c b/blockdev.c
index 97e6897..f5dde19 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -146,6 +146,7 @@ void blockdev_auto_del(BlockBackend *blk)
     DriveInfo *dinfo = blk_legacy_dinfo(blk);
 
     if (dinfo && dinfo->auto_del) {
+        monitor_remove_blk(blk);
         blk_unref(blk);
     }
 }
@@ -606,6 +607,8 @@ static BlockBackend *blockdev_init(const char *file, QDict *bs_opts,
 
     blk_set_on_error(blk, on_read_error, on_write_error);
 
+    monitor_add_blk(blk);
+
 err_no_bs_opts:
     qemu_opts_del(opts);
     return blk;
@@ -2528,6 +2531,8 @@ void hmp_drive_del(Monitor *mon, const QDict *qdict)
         blk_remove_bs(blk);
     }
 
+    monitor_remove_blk(blk);
+
     /* if we have a device attached to this BlockDriverState
      * then we need to make the drive anonymous until the device
      * can be removed.  If this is a drive with no device backing
@@ -3486,6 +3491,7 @@ void qmp_blockdev_add(BlockdevOptions *options, Error **errp)
 
     if (bs && bdrv_key_required(bs)) {
         if (blk) {
+            monitor_remove_blk(blk);
             blk_unref(blk);
         } else {
             QTAILQ_REMOVE(&monitor_bdrv_states, bs, monitor_list);
@@ -3515,6 +3521,7 @@ void qmp_x_blockdev_del(bool has_id, const char *id,
     }
 
     if (has_id) {
+        /* blk_by_name() never returns a BB that is not owned by the monitor */
         blk = blk_by_name(id);
         if (!blk) {
             error_setg(errp, "Cannot find block backend %s", id);
@@ -3562,6 +3569,7 @@ void qmp_x_blockdev_del(bool has_id, const char *id,
     }
 
     if (blk) {
+        monitor_remove_blk(blk);
         blk_unref(blk);
     } else {
         QTAILQ_REMOVE(&monitor_bdrv_states, bs, monitor_list);
diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
index ee36f93..9a3d8db 100644
--- a/include/sysemu/block-backend.h
+++ b/include/sysemu/block-backend.h
@@ -74,6 +74,8 @@ BlockBackend *blk_by_name(const char *name);
 bool blk_name_taken(const char *name);
 BlockBackend *blk_next(BlockBackend *blk);
 BlockBackend *blk_next_inserted(BlockBackend *blk);
+void monitor_add_blk(BlockBackend *blk);
+void monitor_remove_blk(BlockBackend *blk);
 
 BlockDriverState *blk_bs(BlockBackend *blk);
 void blk_remove_bs(BlockBackend *blk);
-- 
2.6.2