support custom weight loader for model runner (#7122)

Co-authored-by: kavioyu <kavioyu@tencent.com>

python/sglang/srt/server_args.py

@@ -234,6 +234,9 @@ class ServerArgs:
     num_reserved_decode_tokens: int = 512  # used for decode kv cache offload in PD
     pdlb_url: Optional[str] = None
 
+    # For model weight update
+    custom_weight_loader: Optional[List[str]] = None
+
     def __post_init__(self):
         # Expert parallelism
         if self.enable_ep_moe:
@@ -538,6 +541,9 @@ class ServerArgs:
             "1" if self.disable_outlines_disk_cache else "0"
         )
 
+        if self.custom_weight_loader is None:
+            self.custom_weight_loader = []
+
     def validate_disagg_tp_size(self, prefill_tp: int, decode_tp: int):
         larger_tp = max(decode_tp, prefill_tp)
         smaller_tp = min(decode_tp, prefill_tp)
@@ -1576,6 +1582,13 @@ class ServerArgs:
             default=None,
             help="The URL of the PD disaggregation load balancer. If set, the prefill/decode server will register with the load balancer.",
         )
+        parser.add_argument(
+            "--custom-weight-loader",
+            type=str,
+            nargs="*",
+            default=None,
+            help="The custom dataloader which used to update the model. Should be set with a valid import path, such as my_package.weight_load_func",
+        )
 
     @classmethod
     def from_cli_args(cls, args: argparse.Namespace):