block/export: Add 'id' option to block-export-add

We'll need an id to identify block exports in monitor commands. This
adds one.

Note that this is different from the 'name' option in the NBD server,
which is the externally visible export name. While block export ids need
to be unique in the whole process, export names must be unique only for
the same server. Different export types or (potentially in the future)
multiple NBD servers can have the same export name externally, but still
need different block export ids internally.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200924152717.287415-19-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/export/export.c

@@ -19,6 +19,7 @@
 #include "block/nbd.h"
 #include "qapi/error.h"
 #include "qapi/qapi-commands-block-export.h"
+#include "qemu/id.h"
 
 static const BlockExportDriver *blk_exp_drivers[] = {
     &blk_exp_nbd,
@@ -28,6 +29,19 @@ static const BlockExportDriver *blk_exp_drivers[] = {
 static QLIST_HEAD(, BlockExport) block_exports =
     QLIST_HEAD_INITIALIZER(block_exports);
 
+static BlockExport *blk_exp_find(const char *id)
+{
+    BlockExport *exp;
+
+    QLIST_FOREACH(exp, &block_exports, next) {
+        if (strcmp(id, exp->id) == 0) {
+            return exp;
+        }
+    }
+
+    return NULL;
+}
+
 static const BlockExportDriver *blk_exp_find_driver(BlockExportType type)
 {
     int i;
@@ -46,6 +60,15 @@ BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
     BlockExport *exp;
     int ret;
 
+    if (!id_wellformed(export->id)) {
+        error_setg(errp, "Invalid block export id");
+        return NULL;
+    }
+    if (blk_exp_find(export->id)) {
+        error_setg(errp, "Block export id '%s' is already in use", export->id);
+        return NULL;
+    }
+
     drv = blk_exp_find_driver(export->type);
     if (!drv) {
         error_setg(errp, "No driver found for the requested export type");
@@ -57,10 +80,12 @@ BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
     *exp = (BlockExport) {
         .drv        = drv,
         .refcount   = 1,
+        .id         = g_strdup(export->id),
     };
 
     ret = drv->create(exp, export, errp);
     if (ret < 0) {
+        g_free(exp->id);
         g_free(exp);
         return NULL;
     }
@@ -87,6 +112,7 @@ static void blk_exp_delete_bh(void *opaque)
     assert(exp->refcount == 0);
     QLIST_REMOVE(exp, next);
     exp->drv->delete(exp);
+    g_free(exp->id);
     g_free(exp);
 
     aio_context_release(aio_context);

blockdev-nbd.c

@@ -269,6 +269,7 @@ void qmp_nbd_server_add(NbdServerAddOptions *arg, Error **errp)
     export_opts = g_new(BlockExportOptions, 1);
     *export_opts = (BlockExportOptions) {
         .type                   = BLOCK_EXPORT_TYPE_NBD,
+        .id                     = g_strdup(arg->name),
         .node_name              = g_strdup(bdrv_get_node_name(bs)),
         .u.nbd = {
             .has_name           = true,

include/block/export.h

@@ -50,6 +50,9 @@ typedef struct BlockExportDriver {
 struct BlockExport {
     const BlockExportDriver *drv;
 
+    /* Unique identifier for the export */
+    char *id;
+
     /*
      * Reference count for this block export. This includes strong references
      * both from the owner (qemu-nbd or the monitor) and clients connected to

qapi/block-export.json

@@ -105,6 +105,8 @@
 #
 # Export a block node to QEMU's embedded NBD server.
 #
+# The export name will be used as the id for the resulting block export.
+#
 # Returns: error if the server is not running, or export with the same name
 #          already exists.
 #
@@ -182,6 +184,8 @@
 # Describes a block export, i.e. how single node should be exported on an
 # external interface.
 #
+# @id: A unique identifier for the block export (across all export types)
+#
 # @node-name: The node name of the block node to be exported (since: 5.2)
 #
 # @writethrough: If true, caches are flushed after every write request to the
@@ -192,6 +196,7 @@
 ##
 { 'union': 'BlockExportOptions',
   'base': { 'type': 'BlockExportType',
+            'id': 'str',
             'node-name': 'str',
             '*writethrough': 'bool' },
   'discriminator': 'type',

qemu-nbd.c

@@ -1064,6 +1064,7 @@ int main(int argc, char **argv)
     export_opts = g_new(BlockExportOptions, 1);
     *export_opts = (BlockExportOptions) {
         .type               = BLOCK_EXPORT_TYPE_NBD,
+        .id                 = g_strdup("qemu-nbd-export"),
         .node_name          = g_strdup(bdrv_get_node_name(bs)),
         .has_writethrough   = true,
         .writethrough       = writethrough,

storage-daemon/qemu-storage-daemon.c

@@ -92,7 +92,7 @@ static void help(void)
 "  --chardev <options>    configure a character device backend\n"
 "                         (see the qemu(1) man page for possible options)\n"
 "\n"
-"  --export [type=]nbd,device=<node-name>[,name=<export-name>]\n"
+"  --export [type=]nbd,device=<node-name>,id=<id>,[,name=<export-name>]\n"
 "           [,writable=on|off][,bitmap=<name>]\n"
 "                         export the specified block node over NBD\n"
 "                         (requires --nbd-server)\n"

tests/qemu-iotests/223.out

@@ -45,7 +45,7 @@ exports available: 0
 {"execute":"nbd-server-add", "arguments":{"device":"nosuch"}}
 {"error": {"class": "GenericError", "desc": "Cannot find device=nosuch nor node_name=nosuch"}}
 {"execute":"nbd-server-add", "arguments":{"device":"n"}}
-{"error": {"class": "GenericError", "desc": "NBD server already has export named 'n'"}}
+{"error": {"class": "GenericError", "desc": "Block export id 'n' is already in use"}}
 {"execute":"nbd-server-add", "arguments":{"device":"n", "name":"n2", "bitmap":"b2"}}
 {"error": {"class": "GenericError", "desc": "Enabled bitmap 'b2' incompatible with readonly export"}}
 {"execute":"nbd-server-add", "arguments":{"device":"n", "name":"n2", "bitmap":"b3"}}
@@ -126,7 +126,7 @@ exports available: 0
 {"execute":"nbd-server-add", "arguments":{"device":"nosuch"}}
 {"error": {"class": "GenericError", "desc": "Cannot find device=nosuch nor node_name=nosuch"}}
 {"execute":"nbd-server-add", "arguments":{"device":"n"}}
-{"error": {"class": "GenericError", "desc": "NBD server already has export named 'n'"}}
+{"error": {"class": "GenericError", "desc": "Block export id 'n' is already in use"}}
 {"execute":"nbd-server-add", "arguments":{"device":"n", "name":"n2", "bitmap":"b2"}}
 {"error": {"class": "GenericError", "desc": "Enabled bitmap 'b2' incompatible with readonly export"}}
 {"execute":"nbd-server-add", "arguments":{"device":"n", "name":"n2", "bitmap":"b3"}}