bdev: add timeout option to bdev_get_bdevs RPC

This opption allows the bdev_get_bdevs RPC to block until a bdev with
specified name appears.  It can be useful, when a bdev is created
asynchronously and the exact moment at which it appears is not known.
For instance, with a discovery service, a bdev is created when a
namespace on a remote NVMeoF target is added, but it's not possible to
specify when that happens exactly.

Signed-off-by: Konrad Sztyber <konrad.sztyber@intel.com>
Change-Id: I6c1f974fba445376ca9d45aac2639202547410cc
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/11960
Community-CI: Mellanox Build Bot
Community-CI: Broadcom CI <spdk-ci.pdl@broadcom.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Shuhei Matsumoto <smatsumoto@nvidia.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>

CHANGELOG.md

@@ -34,6 +34,11 @@ bdev_crypto_create RPC now requires hexlified 'key' and 'key2' params for all pm
 Unhexlifying is performed during RPC command processing and the vbdev crypto module runs on
 binary keys as before.
 
+### bdev
+
+Added a timeout option to the `bdev_get_bdevs` RPC.  It allows the user to specify the amount of
+time to wait until a bdev with a given name appears in the system.
+
 ### bdev_nvme
 
 Added `bdev_nvme_add_error_injection` and `bdev_nvme_remove_error_injection` RPCs to add and

doc/jsonrpc.md

@@ -1607,11 +1607,14 @@ Get information about block devices (bdevs).
 #### Parameters
 
 The user may specify no parameters in order to list all block devices, or a block device may be
-specified by name.
+specified by name.  If a timeout is specified, the method will block until a bdev with a specified
+name appears or the timeout expires.  By default, the timeout is zero, meaning the method returns
+immediately whether the bdev exists or not.
 
 Name                    | Optional | Type        | Description
 ----------------------- | -------- | ----------- | -----------
 name                    | Optional | string      | Block device name
+timeout                 | Optional | number      | Time (ms) to wait for a bdev with specified name to appear
 
 #### Response
 

lib/bdev/bdev_rpc.c

@@ -441,7 +441,15 @@ rpc_dump_bdev_info(struct spdk_json_write_ctx *w,
 }
 
 struct rpc_bdev_get_bdevs {
-	char *name;
+	char		*name;
+	uint64_t	timeout;
+};
+
+struct rpc_bdev_get_bdevs_ctx {
+	struct rpc_bdev_get_bdevs	rpc;
+	struct spdk_jsonrpc_request	*request;
+	struct spdk_poller		*poller;
+	uint64_t			timeout_ticks;
 };
 
 static void
@@ -452,13 +460,45 @@ free_rpc_bdev_get_bdevs(struct rpc_bdev_get_bdevs *r)
 
 static const struct spdk_json_object_decoder rpc_bdev_get_bdevs_decoders[] = {
 	{"name", offsetof(struct rpc_bdev_get_bdevs, name), spdk_json_decode_string, true},
+	{"timeout", offsetof(struct rpc_bdev_get_bdevs, timeout), spdk_json_decode_uint64, true},
 };
 
+static int
+get_bdevs_poller(void *_ctx)
+{
+	struct rpc_bdev_get_bdevs_ctx *ctx = _ctx;
+	struct spdk_json_write_ctx *w;
+	struct spdk_bdev *bdev;
+
+	bdev = spdk_bdev_get_by_name(ctx->rpc.name);
+	if (bdev == NULL && spdk_get_ticks() < ctx->timeout_ticks) {
+		return SPDK_POLLER_BUSY;
+	}
+
+	if (bdev == NULL) {
+		SPDK_ERRLOG("Timed out while waiting for bdev '%s' to appear\n", ctx->rpc.name);
+		spdk_jsonrpc_send_error_response(ctx->request, -ENODEV, spdk_strerror(ENODEV));
+	} else {
+		w = spdk_jsonrpc_begin_result(ctx->request);
+		spdk_json_write_array_begin(w);
+		rpc_dump_bdev_info(w, bdev);
+		spdk_json_write_array_end(w);
+		spdk_jsonrpc_end_result(ctx->request, w);
+	}
+
+	spdk_poller_unregister(&ctx->poller);
+	free_rpc_bdev_get_bdevs(&ctx->rpc);
+	free(ctx);
+
+	return SPDK_POLLER_BUSY;
+}
+
 static void
 rpc_bdev_get_bdevs(struct spdk_jsonrpc_request *request,
 		   const struct spdk_json_val *params)
 {
 	struct rpc_bdev_get_bdevs req = {};
+	struct rpc_bdev_get_bdevs_ctx *ctx;
 	struct spdk_json_write_ctx *w;
 	struct spdk_bdev *bdev = NULL;
 
@@ -475,9 +515,34 @@ rpc_bdev_get_bdevs(struct spdk_jsonrpc_request *request,
 	if (req.name) {
 		bdev = spdk_bdev_get_by_name(req.name);
 		if (bdev == NULL) {
-			SPDK_ERRLOG("bdev '%s' does not exist\n", req.name);
-			spdk_jsonrpc_send_error_response(request, -ENODEV, spdk_strerror(ENODEV));
-			free_rpc_bdev_get_bdevs(&req);
+			if (req.timeout == 0) {
+				SPDK_ERRLOG("bdev '%s' does not exist\n", req.name);
+				spdk_jsonrpc_send_error_response(request, -ENODEV, spdk_strerror(ENODEV));
+				free_rpc_bdev_get_bdevs(&req);
+				return;
+			}
+
+			ctx = calloc(1, sizeof(*ctx));
+			if (ctx == NULL) {
+				SPDK_ERRLOG("Failed to allocate bdev_get_bdevs context\n");
+				spdk_jsonrpc_send_error_response(request, -ENOMEM, spdk_strerror(ENOMEM));
+				free_rpc_bdev_get_bdevs(&req);
+				return;
+			}
+
+			ctx->poller = SPDK_POLLER_REGISTER(get_bdevs_poller, ctx, 10 * 1000);
+			if (ctx->poller == NULL) {
+				SPDK_ERRLOG("Failed to register bdev_get_bdevs poller\n");
+				spdk_jsonrpc_send_error_response(request, -ENOMEM, spdk_strerror(ENOMEM));
+				free_rpc_bdev_get_bdevs(&req);
+				free(ctx);
+				return;
+			}
+
+			memcpy(&ctx->rpc, &req, sizeof(req));
+			ctx->timeout_ticks = spdk_get_ticks() + req.timeout *
+					     spdk_get_ticks_hz() / 1000ull;
+			ctx->request = request;
 			return;
 		}
 	}

scripts/rpc.py

@@ -1003,11 +1003,15 @@ if __name__ == "__main__":
 
     def bdev_get_bdevs(args):
         print_dict(rpc.bdev.bdev_get_bdevs(args.client,
-                                           name=args.name))
+                                           name=args.name, timeout=args.timeout_ms))
 
     p = subparsers.add_parser('bdev_get_bdevs', aliases=['get_bdevs'],
                               help='Display current blockdev list or required blockdev')
     p.add_argument('-b', '--name', help="Name of the Blockdev. Example: Nvme0n1", required=False)
+    p.add_argument('-t', '--timeout-ms', help="""Time in ms to wait for the bdev to appear (only used
+    with the -b|--name option). The default timeout is 0, meaning the RPC returns immediately
+    whether the bdev exists or not.""",
+                   type=int, required=False)
     p.set_defaults(func=bdev_get_bdevs)
 
     def bdev_get_iostat(args):

scripts/rpc/bdev.py

@@ -1281,11 +1281,12 @@ def bdev_ftl_delete(client, name):
 
 
 @deprecated_alias('get_bdevs')
-def bdev_get_bdevs(client, name=None):
+def bdev_get_bdevs(client, name=None, timeout=None):
     """Get information about block devices.
 
     Args:
         name: bdev name to query (optional; if omitted, query all bdevs)
+        timeout: time in ms to wait for the bdev with specified name to appear
 
     Returns:
         List of bdev information objects.
@@ -1293,6 +1294,8 @@ def bdev_get_bdevs(client, name=None):
     params = {}
     if name:
         params['name'] = name
+    if timeout:
+        params['timeout'] = timeout
     return client.call('bdev_get_bdevs', params)