block/export: Remove magic from block-export-add

nbd-server-add tries to be convenient and adds two questionable
features that we don't want to share in block-export-add, even for NBD
exports:

1. When requesting a writable export of a read-only device, the export
   is silently downgraded to read-only. This should be an error in the
   context of block-export-add.

2. When using a BlockBackend name, unplugging the device from the guest
   will automatically stop the NBD server, too. This may sometimes be
   what you want, but it could also be very surprising. Let's keep
   things explicit with block-export-add. If the user wants to stop the
   export, they should tell us so.

Move these things into the nbd-server-add QMP command handler so that
they apply only there.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200924152717.287415-8-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

diff --git a/block/export/export.c b/block/export/export.c
index fd65541963faaa41d730ba0caf15312f31e276e9..05bc5e37447bc7aebb10df48a617945891db246d 100644 (file)
--- a/block/export/export.c
+++ b/block/export/export.c
@@ -13,6 +13,8 @@
 
 #include "qemu/osdep.h"
 
+#include "block/block.h"
+#include "sysemu/block-backend.h"
 #include "block/export.h"
 #include "block/nbd.h"
 #include "qapi/error.h"
@@ -34,15 +36,20 @@ static const BlockExportDriver *blk_exp_find_driver(BlockExportType type)
     return NULL;
 }
 
-void qmp_block_export_add(BlockExportOptions *export, Error **errp)
+BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
 {
     const BlockExportDriver *drv;
 
     drv = blk_exp_find_driver(export->type);
     if (!drv) {
         error_setg(errp, "No driver found for the requested export type");
-        return;
+        return NULL;
     }
 
-    drv->create(export, errp);
+    return drv->create(export, errp);
+}
+
+void qmp_block_export_add(BlockExportOptions *export, Error **errp)
+{
+    blk_exp_add(export, errp);
 }

diff --git a/blockdev-nbd.c b/blockdev-nbd.c
index 96cb0100e94b513529e82ed0810531f120cc1e82..7bcca105f9791e6c369c59ac9f10acc82f2744af 100644 (file)
--- a/blockdev-nbd.c
+++ b/blockdev-nbd.c
@@ -152,7 +152,6 @@ BlockExport *nbd_export_create(BlockExportOptions *exp_args, Error **errp)
 {
     BlockExportOptionsNbd *arg = &exp_args->u.nbd;
     BlockDriverState *bs = NULL;
-    BlockBackend *on_eject_blk;
     NBDExport *exp = NULL;
     AioContext *aio_context;
 
@@ -182,8 +181,6 @@ BlockExport *nbd_export_create(BlockExportOptions *exp_args, Error **errp)
         return NULL;
     }
 
-    on_eject_blk = blk_by_name(arg->device);
-
     bs = bdrv_lookup_bs(arg->device, arg->device, errp);
     if (!bs) {
         return NULL;
@@ -195,13 +192,14 @@ BlockExport *nbd_export_create(BlockExportOptions *exp_args, Error **errp)
     if (!arg->has_writable) {
         arg->writable = false;
     }
-    if (bdrv_is_read_only(bs)) {
-        arg->writable = false;
+    if (bdrv_is_read_only(bs) && arg->writable) {
+        error_setg(errp, "Cannot export read-only node as writable");
+        goto out;
     }
 
     exp = nbd_export_new(bs, arg->name, arg->description, arg->bitmap,
                          !arg->writable, !arg->writable,
-                         NULL, false, on_eject_blk, errp);
+                         NULL, false, errp);
     if (!exp) {
         goto out;
     }
@@ -219,11 +217,44 @@ BlockExport *nbd_export_create(BlockExportOptions *exp_args, Error **errp)
 
 void qmp_nbd_server_add(BlockExportOptionsNbd *arg, Error **errp)
 {
-    BlockExportOptions export = {
+    BlockExport *export;
+    BlockDriverState *bs;
+    BlockBackend *on_eject_blk;
+    BlockExportOptions export_opts;
+
+    bs = bdrv_lookup_bs(arg->device, arg->device, errp);
+    if (!bs) {
+        return;
+    }
+
+    export_opts = (BlockExportOptions) {
         .type = BLOCK_EXPORT_TYPE_NBD,
         .u.nbd = *arg,
     };
-    qmp_block_export_add(&export, errp);
+
+    /*
+     * nbd-server-add doesn't complain when a read-only device should be
+     * exported as writable, but simply downgrades it. This is an error with
+     * block-export-add.
+     */
+    if (bdrv_is_read_only(bs)) {
+        export_opts.u.nbd.has_writable = true;
+        export_opts.u.nbd.writable = false;
+    }
+
+    export = blk_exp_add(&export_opts, errp);
+    if (!export) {
+        return;
+    }
+
+    /*
+     * nbd-server-add removes the export when the named BlockBackend used for
+     * @device goes away.
+     */
+    on_eject_blk = blk_by_name(arg->device);
+    if (on_eject_blk) {
+        nbd_export_set_on_eject_blk(export, on_eject_blk);
+    }
 }
 
 void qmp_nbd_server_remove(const char *name,

diff --git a/include/block/export.h b/include/block/export.h
index 42e3c055fc24455db5c06a184ef073fde9729387..e7af2c768742c1c7df2e60dfca39ec9f02bed09e 100644 (file)
--- a/include/block/export.h
+++ b/include/block/export.h
@@ -30,4 +30,6 @@ struct BlockExport {
     const BlockExportDriver *drv;
 };
 
+BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp);
+
 #endif

diff --git a/include/block/nbd.h b/include/block/nbd.h
index 451f399b0af535232c80efd3fbd553205a85d505..f55f5b710b1a385295b6e6987b61b6afd404ec85 100644 (file)
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -335,7 +335,8 @@ NBDExport *nbd_export_new(BlockDriverState *bs,
                           const char *name, const char *desc,
                           const char *bitmap, bool readonly, bool shared,
                           void (*close)(NBDExport *), bool writethrough,
-                          BlockBackend *on_eject_blk, Error **errp);
+                          Error **errp);
+void nbd_export_set_on_eject_blk(BlockExport *exp, BlockBackend *blk);
 void nbd_export_close(NBDExport *exp);
 void nbd_export_remove(NBDExport *exp, NbdServerRemoveMode mode, Error **errp);
 void nbd_export_get(NBDExport *exp);

diff --git a/nbd/server.c b/nbd/server.c
index 33aaca918c493035735c97e4c626677de454dc75..23d9a530944e6ea81de041e5e393469ec69380d9 100644 (file)
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -1506,11 +1506,23 @@ static void nbd_eject_notifier(Notifier *n, void *data)
     aio_context_release(aio_context);
 }
 
+void nbd_export_set_on_eject_blk(BlockExport *exp, BlockBackend *blk)
+{
+    NBDExport *nbd_exp = container_of(exp, NBDExport, common);
+    assert(exp->drv == &blk_exp_nbd);
+    assert(nbd_exp->eject_notifier_blk == NULL);
+
+    blk_ref(blk);
+    nbd_exp->eject_notifier_blk = blk;
+    nbd_exp->eject_notifier.notify = nbd_eject_notifier;
+    blk_add_remove_bs_notifier(blk, &nbd_exp->eject_notifier);
+}
+
 NBDExport *nbd_export_new(BlockDriverState *bs,
                           const char *name, const char *desc,
                           const char *bitmap, bool readonly, bool shared,
                           void (*close)(NBDExport *), bool writethrough,
-                          BlockBackend *on_eject_blk, Error **errp)
+                          Error **errp)
 {
     AioContext *ctx;
     BlockBackend *blk;
@@ -1617,12 +1629,6 @@ NBDExport *nbd_export_new(BlockDriverState *bs,
     exp->ctx = ctx;
     blk_add_aio_context_notifier(blk, blk_aio_attached, blk_aio_detach, exp);
 
-    if (on_eject_blk) {
-        blk_ref(on_eject_blk);
-        exp->eject_notifier_blk = on_eject_blk;
-        exp->eject_notifier.notify = nbd_eject_notifier;
-        blk_add_remove_bs_notifier(on_eject_blk, &exp->eject_notifier);
-    }
     QTAILQ_INSERT_TAIL(&exports, exp, next);
     nbd_export_get(exp);
     return exp;

diff --git a/qemu-nbd.c b/qemu-nbd.c
index 16473d809cd302ae6abf8e1f21cbec51b4b18b85..b2a0ea6c5eeb085f6f5af5eaf9e6e28b67dceb07 100644 (file)
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -1067,8 +1067,7 @@ int main(int argc, char **argv)
 
     export = nbd_export_new(bs, export_name,
                             export_description, bitmap, readonly, shared > 1,
-                            nbd_export_closed, writethrough, NULL,
-                            &error_fatal);
+                            nbd_export_closed, writethrough, &error_fatal);
 
     if (device) {
 #if HAVE_NBD_DEVICE