[Qemu-devel] [PATCH 02/16] Implement drive_del to decouple block removal from device removal

[Kevin Wolf <kwolf@redhat.com>]

From: Ryan Harper <ryanh@us.ibm.com>

Currently device hotplug removal code is tied to device removal via
ACPI.  All pci devices that are removable via device_del() require the
guest to respond to the request.  In some cases the guest may not
respond leaving the device still accessible to the guest.  The management
layer doesn't currently have a reliable way to revoke access to host
resource in the presence of an uncooperative guest.

This patch implements a new monitor command, drive_del, which
provides an explicit command to revoke access to a host block device.

drive_del first quiesces the block device (qemu_aio_flush;
bdrv_flush() and bdrv_close()).  This prevents further IO from being
submitted against the host device.  Finally, drive_del cleans up
pointers between the drive object (host resource) and the device
object (guest resource).

Signed-off-by: Ryan Harper <ryanh@us.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 blockdev.c      |   39 +++++++++++++++++++++++++++++++++++++++
 blockdev.h      |    1 +
 hmp-commands.hx |   18 ++++++++++++++++++
 3 files changed, 58 insertions(+), 0 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index 6cb179a..f6ac439 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -14,6 +14,8 @@
 #include "qemu-option.h"
 #include "qemu-config.h"
 #include "sysemu.h"
+#include "hw/qdev.h"
+#include "block_int.h"
 
 static QTAILQ_HEAD(drivelist, DriveInfo) drives = QTAILQ_HEAD_INITIALIZER(drives);
 
@@ -597,3 +599,40 @@ int do_change_block(Monitor *mon, const char *device,
     }
     return monitor_read_bdrv_key_start(mon, bs, NULL, NULL);
 }
+
+int do_drive_del(Monitor *mon, const QDict *qdict, QObject **ret_data)
+{
+    const char *id = qdict_get_str(qdict, "id");
+    BlockDriverState *bs;
+    BlockDriverState **ptr;
+    Property *prop;
+
+    bs = bdrv_find(id);
+    if (!bs) {
+        qerror_report(QERR_DEVICE_NOT_FOUND, id);
+        return -1;
+    }
+
+    /* quiesce block driver; prevent further io */
+    qemu_aio_flush();
+    bdrv_flush(bs);
+    bdrv_close(bs);
+
+    /* clean up guest state from pointing to host resource by
+     * finding and removing DeviceState "drive" property */
+    for (prop = bs->peer->info->props; prop && prop->name; prop++) {
+        if (prop->info->type == PROP_TYPE_DRIVE) {
+            ptr = qdev_get_prop_ptr(bs->peer, prop);
+            if ((*ptr) == bs) {
+                bdrv_detach(bs, bs->peer);
+                *ptr = NULL;
+                break;
+            }
+        }
+    }
+
+    /* clean up host side */
+    drive_uninit(drive_get_by_blockdev(bs));
+
+    return 0;
+}
diff --git a/blockdev.h b/blockdev.h
index 653affc..2a0559e 100644
--- a/blockdev.h
+++ b/blockdev.h
@@ -51,5 +51,6 @@ int do_eject(Monitor *mon, const QDict *qdict, QObject **ret_data);
 int do_block_set_passwd(Monitor *mon, const QDict *qdict, QObject **ret_data);
 int do_change_block(Monitor *mon, const char *device,
                     const char *filename, const char *fmt);
+int do_drive_del(Monitor *mon, const QDict *qdict, QObject **ret_data);
 
 #endif
diff --git a/hmp-commands.hx b/hmp-commands.hx
index e5585ba..23024ba 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -68,6 +68,24 @@ Eject a removable medium (use -f to force it).
 ETEXI
 
     {
+        .name       = "drive_del",
+        .args_type  = "id:s",
+        .params     = "device",
+        .help       = "remove host block device",
+        .user_print = monitor_user_noop,
+        .mhandler.cmd_new = do_drive_del,
+    },
+
+STEXI
+@item drive_del @var{device}
+@findex drive_del
+Remove host block device.  The result is that guest generated IO is no longer
+submitted against the host device underlying the disk.  Once a drive has
+been deleted, the QEMU Block layer returns -EIO which results in IO
+errors in the guest for applications that are reading/writing to the device.
+ETEXI
+
+    {
         .name       = "change",
         .args_type  = "device:B,target:F,arg:s?",
         .params     = "device filename [format]",
-- 
1.7.2.3