dpll: fix device-id-get and pin-id-get to return errors properly

JIRA: https://issues.redhat.com/browse/RHEL-126529

Upstream commit(s):
commit 36fedc4
Author: Petr Oros <poros@redhat.com>
Date:   Fri Oct 24 21:07:33 2025 +0200

    dpll: fix device-id-get and pin-id-get to return errors properly

    The device-id-get and pin-id-get handlers were ignoring errors from
    the find functions and sending empty replies instead of returning
    error codes to userspace.

    When dpll_device_find_from_nlattr() or dpll_pin_find_from_nlattr()
    returned an error (e.g., -EINVAL for "multiple matches" or -ENODEV
    for "not found"), the handlers checked `if (!IS_ERR(ptr))` and
    skipped adding the device/pin handle to the message, but then still
    sent the empty message as a successful reply.

    This caused userspace tools to receive empty responses with id=0
    instead of proper netlink errors with extack messages like
    "multiple matches".

    The bug is visible via strace, which shows the kernel sending TWO
    netlink messages in response to a single request:

    1. Empty reply (20 bytes, just header, no attributes):
       recvfrom(3, [{nlmsg_len=20, nlmsg_type=dpll, nlmsg_flags=0, ...},
                    {cmd=0x7, version=1}], ...)

    2. NLMSG_ERROR ACK with extack (because of NLM_F_ACK flag):
       recvfrom(3, [{nlmsg_len=60, nlmsg_type=NLMSG_ERROR,
                     nlmsg_flags=NLM_F_CAPPED|NLM_F_ACK_TLVS, ...},
                    [{error=0, msg={...}},
                     [{nla_type=NLMSGERR_ATTR_MSG}, "multiple matches"]]], ...)

    The C YNL library parses the first message, sees an empty response,
    and creates a result object with calloc() which zero-initializes all
    fields, resulting in id=0.

    The Python YNL library parses both messages and displays the extack
    from the second NLMSG_ERROR message.

    Fix by checking `if (IS_ERR(ptr))` first and returning the error
    code immediately, so that netlink properly sends only NLMSG_ERROR with
    the extack message to userspace. After this fix, both C and Python
    YNL tools receive only the NLMSG_ERROR and behave consistently.

    This affects:
    - DPLL_CMD_DEVICE_ID_GET: now properly returns error when multiple
      devices match the criteria (e.g., same module-name + clock-id)
    - DPLL_CMD_PIN_ID_GET: now properly returns error when multiple pins
      match the criteria (e.g., same module-name)

    Before fix:
      $ dpll pin id-get module-name ice
      0  (wrong - should be error, there are 17 pins with module-name "ice")

    After fix:
      $ dpll pin id-get module-name ice
      Error: multiple matches
      (correct - kernel reports the ambiguity via extack)

    Fixes: 9d71b54 ("dpll: netlink: Add DPLL framework base functions")
    Signed-off-by: Petr Oros <poros@redhat.com>
    Reviewed-by: Ivan Vecera <ivecera@redhat.com>
    Link: https://patch.msgid.link/20251024190733.364101-1-poros@redhat.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Petr Oros <poros@redhat.com>

Author: orosp

drivers/dpll/dpll_netlink.c

@@ -1559,16 +1559,18 @@ int dpll_nl_pin_id_get_doit(struct sk_buff *skb, struct genl_info *info)
 		return -EMSGSIZE;
 	}
 	pin = dpll_pin_find_from_nlattr(info);
-	if (!IS_ERR(pin)) {
-		if (!dpll_pin_available(pin)) {
-			nlmsg_free(msg);
-			return -ENODEV;
-		}
-		ret = dpll_msg_add_pin_handle(msg, pin);
-		if (ret) {
-			nlmsg_free(msg);
-			return ret;
-		}
+	if (IS_ERR(pin)) {
+		nlmsg_free(msg);
+		return PTR_ERR(pin);
+	}
+	if (!dpll_pin_available(pin)) {
+		nlmsg_free(msg);
+		return -ENODEV;
+	}
+	ret = dpll_msg_add_pin_handle(msg, pin);
+	if (ret) {
+		nlmsg_free(msg);
+		return ret;
 	}
 	genlmsg_end(msg, hdr);
 
@@ -1735,12 +1737,14 @@ int dpll_nl_device_id_get_doit(struct sk_buff *skb, struct genl_info *info)
 	}
 
 	dpll = dpll_device_find_from_nlattr(info);
-	if (!IS_ERR(dpll)) {
-		ret = dpll_msg_add_dev_handle(msg, dpll);
-		if (ret) {
-			nlmsg_free(msg);
-			return ret;
-		}
+	if (IS_ERR(dpll)) {
+		nlmsg_free(msg);
+		return PTR_ERR(dpll);
+	}
+	ret = dpll_msg_add_dev_handle(msg, dpll);
+	if (ret) {
+		nlmsg_free(msg);
+		return ret;
 	}
 	genlmsg_end(msg, hdr);