[Qemu-devel] [PULL 18/40] hmp: 'drive_add -n' for creating a node without BB

[Kevin Wolf <kwolf@redhat.com>]

This patch adds an option to the drive_add HMP command to create only a
BlockDriverState without a BlockBackend on top.

The motivation for this is that libvirt needs to specify options to a
migration target (specifically, detect-zeroes). drive-mirror doesn't
allow specifying options, and the proper way to do this is to create the
target BDS separately with blockdev-add (where you can specify options)
and then use blockdev-mirror to that BDS.

However, libvirt can't use blockdev-add as long as it is still
experimental, and we're expecting that it will still take some time, so
we need to resort to drive_add.

The problem with drive_add is that so far it always created a BB, and
BDSes with a BB can't be used as a mirroring target as long as we don't
support multiple BBs per BDS - and while we're working towards that
goal, it's another thing that will still take some time.

So to achieve the goal, the simplest solution to provide the
functionality now without adding one-off options to the mirror QMP
commands is to extend drive_add to create nodes without BBs.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 blockdev.c                | 30 ++++++++++++++++++++++++++++++
 device-hotplug.c          |  7 +++++++
 hmp-commands.hx           |  4 ++--
 include/block/block_int.h |  2 ++
 4 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index 1824cae..1297c90 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -3875,6 +3875,36 @@ out:
     aio_context_release(aio_context);
 }
 
+void hmp_drive_add_node(Monitor *mon, const char *optstr)
+{
+    QemuOpts *opts;
+    QDict *qdict;
+    Error *local_err = NULL;
+
+    opts = qemu_opts_parse_noisily(&qemu_drive_opts, optstr, false);
+    if (!opts) {
+        return;
+    }
+
+    qdict = qemu_opts_to_qdict(opts, NULL);
+
+    if (!qdict_get_try_str(qdict, "node-name")) {
+        error_report("'node-name' needs to be specified");
+        goto out;
+    }
+
+    BlockDriverState *bs = bds_tree_init(qdict, &local_err);
+    if (!bs) {
+        error_report_err(local_err);
+        goto out;
+    }
+
+    QTAILQ_INSERT_TAIL(&monitor_bdrv_states, bs, monitor_list);
+
+out:
+    qemu_opts_del(opts);
+}
+
 void qmp_blockdev_add(BlockdevOptions *options, Error **errp)
 {
     QmpOutputVisitor *ov = qmp_output_visitor_new();
diff --git a/device-hotplug.c b/device-hotplug.c
index 9a7cd66..3e5cdaa 100644
--- a/device-hotplug.c
+++ b/device-hotplug.c
@@ -30,6 +30,7 @@
 #include "qemu/config-file.h"
 #include "sysemu/sysemu.h"
 #include "monitor/monitor.h"
+#include "block/block_int.h"
 
 static DriveInfo *add_init_drive(const char *optstr)
 {
@@ -55,6 +56,12 @@ void hmp_drive_add(Monitor *mon, const QDict *qdict)
 {
     DriveInfo *dinfo = NULL;
     const char *opts = qdict_get_str(qdict, "opts");
+    bool node = qdict_get_try_bool(qdict, "node", false);
+
+    if (node) {
+        hmp_drive_add_node(mon, opts);
+        return;
+    }
 
     dinfo = add_init_drive(opts);
     if (!dinfo) {
diff --git a/hmp-commands.hx b/hmp-commands.hx
index 639205b..4f4f60a 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -1201,8 +1201,8 @@ ETEXI
 
     {
         .name       = "drive_add",
-        .args_type  = "pci_addr:s,opts:s",
-        .params     = "[[<domain>:]<bus>:]<slot>\n"
+        .args_type  = "node:-n,pci_addr:s,opts:s",
+        .params     = "[-n] [[<domain>:]<bus>:]<slot>\n"
                       "[file=file][,if=type][,bus=n]\n"
                       "[,unit=m][,media=d][,index=i]\n"
                       "[,cyls=c,heads=h,secs=s[,trans=t]]\n"
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 9ef823a..dda5ba0 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -694,6 +694,8 @@ void backup_start(BlockDriverState *bs, BlockDriverState *target,
                   BlockCompletionFunc *cb, void *opaque,
                   BlockJobTxn *txn, Error **errp);
 
+void hmp_drive_add_node(Monitor *mon, const char *optstr);
+
 void blk_set_bs(BlockBackend *blk, BlockDriverState *bs);
 
 void blk_dev_change_media_cb(BlockBackend *blk, bool load);
-- 
1.8.3.1