Fix: Mac80211 NSS Dynamic VLAN Patch Fails

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Fix: mac80211 NSS Dynamic VLAN Patch Fails

Hey guys! Today, we're diving deep into a tricky issue that some of you might have encountered while working with OpenWrt on IPQ807x devices. Specifically, we're talking about the dreaded mac80211 NSS Dynamic VLAN patch failing to apply. If you've been pulling your hair out over this, don't worry – you're in the right place. Let's break down the problem, understand why it happens, and explore how to fix it.

Understanding the Bug: A Deep Dive

So, what's the deal with this bug? In essence, it's a patching problem that arises when you're trying to apply a specific patch (236-003-ath11k-add-dynamic-VLAN-support-in-NSS-offload.patch) to the mac80211 package within your OpenWrt build environment. This patch is crucial for enabling dynamic VLAN support with NSS (Network Subsystem) offload, which is a key feature for devices like the MX4300 and others in the IPQ807x family. NSS offload essentially helps to offload network processing tasks from the main CPU to a dedicated hardware component, improving performance and reducing CPU load.

The error typically manifests during the build process, and you'll likely see a message indicating that a particular 'hunk' within the patch has failed to apply. A 'hunk' is simply a chunk of code that the patch is trying to modify or add. The error message often points to line number mismatches within the drivers/net/wireless/ath/ath11k/mac.c file. This file is a critical part of the ath11k driver, which is responsible for handling Wi-Fi functionality on these devices.

The Technical Details

To get a bit more technical, the issue stems from the fact that the patch was originally created for an older version of the backports package. Backports, in this context, are essentially updates and improvements to kernel drivers that are backported from newer kernel versions to older ones. The OpenWrt build system uses backports to keep the mac80211 package up-to-date with the latest features and bug fixes.

The problem arises when the structure of the mac.c file changes between backports versions. In this case, the current backports version (backports-6.12.52 at the time of this writing) has structural differences compared to the version for which the patch was originally designed. These differences lead to the line number mismatches, causing the patch to fail. It’s like trying to fit a puzzle piece into the wrong spot – it just won't go!

Impact and Why It Matters

The impact of this bug is significant, especially if you rely on dynamic VLAN support for your network setup. Dynamic VLANs allow you to create and manage VLANs on the fly, which is incredibly useful for isolating network traffic, improving security, and managing different network segments. Without this patch, you're essentially losing out on a critical feature that can significantly enhance your network's capabilities.

From a severity standpoint, this is a high-priority issue. NSS offload is a cornerstone of the IPQ807x platform's performance, and dynamic VLAN support is a crucial feature for many advanced network configurations. If you're building a custom OpenWrt image for your IPQ807x device, encountering this error can be a major roadblock.

Decoding the Error Output: What the Logs Tell Us

When the patch fails, the build process spits out a bunch of error messages that might seem cryptic at first glance. But don't worry, we can decipher them! The key part of the error output looks something like this:

Applying /home/ubuntu/openwrt-ipq/package/kernel/mac80211/patches/nss/ath11k/236-003-ath11k-add-dynamic-VLAN-support-in-NSS-offload.patch using plaintext:
patching file drivers/net/wireless/ath/ath11k/mac.cHunk #3 succeeded at 4296 with fuzz 2.
Hunk #4 FAILED at 4389.
Hunk #5 succeeded at 4448 (offset 33 lines).
...
1 out of 18 hunks FAILED -- saving rejects to file drivers/net/wireless/ath/ath11k/mac.c.rej
Patch failed!  Please fix /home/ubuntu/openwrt-ipq/package/kernel/mac80211/patches/nss/ath11k/236-003-ath11k-add-dynamic-VLAN-support-in-NSS-offload.patch!
make[2]: *** [Makefile:481: /home/ubuntu/openwrt-ipq/build_dir/target-aarch64_cortex-a53_musl/linux-qualcommax_ipq807x/mac80211-regular/backports-6.12.52/.prepared_...] Error 1
ERROR: package/kernel/mac80211 failed to build (build variant: regular).

Let's break this down:

  • Applying ... 236-003 ... patch using plaintext: This tells you which patch is being applied when the error occurs.
  • patching file drivers/net/wireless/ath/ath11k/mac.c: This indicates the file that the patch is trying to modify.
  • Hunk #4 FAILED at 4389: This is the crucial part. It means that 'Hunk #4' of the patch failed to apply at line 4389 in the mac.c file. This line number mismatch is the core of the problem.
  • 1 out of 18 hunks FAILED: This tells you that one hunk out of the 18 hunks in the patch failed.
  • Patch failed!: This is the obvious conclusion – the patch application failed.
  • saving rejects to file drivers/net/wireless/ath/ath11k/mac.c.rej: This is helpful for debugging. The .rej file contains the rejected hunks, allowing you to inspect the differences between the patch and the current file.
  • ERROR: package/kernel/mac80211 failed to build: This confirms that the build process failed due to the patch application error.

Examining the Rejected Hunk

The .rej file mentioned in the error output is a treasure trove of information. It shows you exactly what the patch was trying to do and why it failed. A typical rejected hunk might look like this:

---
drivers/net/wireless/ath/ath11k/mac.c
+++
drivers/net/wireless/ath/ath11k/mac.c
@@ -4389,15 +4423,40 @@
        return first_errno;
}
 
+static int ath11k_get_vlan_groupkey_index(struct ath11k_vif *arvif,
+                                         struct ieee80211_key_conf *key)
+{
+       struct ath11k *ar = arvif->ar;
+       int map_idx = 0;
+       int free_bit;
+
+       for (map_idx = 0; map_idx < ATH11K_FREE_GROUP_IDX_MAP_MAX; map_idx++)
+               if (arvif->free_groupidx_map[map_idx] != 0)
+                       break;
+
+       if (map_idx == ATH11K_FREE_GROUP_IDX_MAP_MAX)
+               return -ENOSPC;
+
+       spin_lock_bh(&ar->data_lock);
+       /* select the first free key index */
+       free_bit = __ffs64(arvif->free_groupidx_map[map_idx]);
+       key->hw_key_idx = (map_idx * ATH11K_FREE_GROUP_IDX_MAP_BITS) + free_bit;
+       /* clear the selected bit from free index map */
+       clear_bit(key->hw_key_idx, arvif->free_groupidx_map);
+       spin_unlock_bh(&ar->data_lock);
+
+       return 0;
+}
+
 static int ath11k_mac_op_set_key(struct ieee80211_hw *hw, enum set_key_cmd cmd,
                                 struct ieee80211_vif *vif, struct ieee80211_sta *sta,
                                 struct ieee80211_key_conf *key)

The --- and +++ indicate the original and modified versions of the code, respectively. The @@ -4389,15 +4423,40 @@ line shows the line number where the patch was supposed to be applied (4389 in the original file, 4423 in the patched file), and the 15 and 40 represent the number of lines in each section. The code block within the diff shows the actual changes the patch was trying to make. By examining this, you can often get a sense of why the patch failed – the surrounding code might be different in the current version of the file.

The Root Cause: Why the Patch Fails

Okay, we've seen the error messages and dissected the .rej file. But why does this happen in the first place? The root cause, as mentioned earlier, is the mismatch between the patch's expectations and the current state of the mac.c file. This mismatch typically arises due to updates in the backports package.

Imagine the mac.c file as a living document that gets revised and updated over time. The patch is like a set of instructions for making specific changes to that document. If the document's structure changes significantly between the time the instructions were written and the time they're executed, the instructions might no longer be valid. Line numbers might shift, code blocks might be rearranged, and new code might be inserted, all of which can throw off the patch application process.

In this specific case, the 236-003 patch was likely created for an older version of the backports package. When you're building OpenWrt with a newer backports version (6.12.52 in this instance), the mac.c file has evolved, and the patch's line number references are no longer accurate. This is why you see the 'Hunk #4 FAILED at 4389' error – the patch is trying to modify a line that either doesn't exist or contains different code than it expects.

Identifying the Culprit: Backports Versioning

The key takeaway here is the importance of backports versioning. Patches are often tied to specific versions of the code they're intended to modify. When you're working with a complex system like OpenWrt, which involves numerous packages and dependencies, it's crucial to ensure that your patches are compatible with the versions of the underlying libraries and drivers.

In this scenario, the mac80211 package, which includes the ath11k driver, is heavily influenced by the backports package. If you're using a backports version that's significantly different from the one for which the 236-003 patch was designed, you're likely to encounter patching issues. This is a common challenge in software development, especially when dealing with constantly evolving projects.

Temporary Workaround: A Quick Fix (But Not a Solution)

If you're in a bind and need to get your build working quickly, there's a temporary workaround you can use: disable the problematic patch. This will allow the build process to complete, but it comes at the cost of losing the dynamic VLAN support functionality.

Here's how you can disable the patch:

mv package/kernel/mac80211/patches/nss/ath11k/236-003-ath11k-add-dynamic-VLAN-support-in-NSS-offload.patch \
   package/kernel/mac80211/patches/nss/ath11k/236-003-ath11k-add-dynamic-VLAN-support-in-NSS-offload.patch.disabled

This command essentially renames the patch file, preventing the build system from applying it. By adding the .disabled suffix, you're signaling that the patch should be ignored.

Important Caveats

It's crucial to understand that this workaround is just a temporary measure. Disabling the patch means you're losing the dynamic VLAN support feature, which might be critical for your network setup. This workaround is primarily useful for troubleshooting and for getting a build working temporarily while you investigate the underlying issue.

Think of this workaround as putting a bandage on a wound – it stops the bleeding, but it doesn't heal the injury. The real solution is to address the root cause of the problem, which, in this case, is the patch incompatibility.

The Real Solution: Updating the Patch

The ultimate solution to this problem is to update the 236-003 patch to be compatible with the current backports version (6.12.52 or later). This involves examining the rejected hunks, understanding the changes in the mac.c file, and adjusting the patch accordingly.

Unfortunately, updating a patch can be a complex and time-consuming task, especially if you're not intimately familiar with the codebase. It requires a good understanding of the code being modified, the purpose of the patch, and the changes that have occurred in the file since the patch was created.

Steps to Update the Patch

Here's a general outline of the steps involved in updating the patch:

  1. Examine the .rej file: The .rej file provides valuable clues about why the patch failed. It shows you the exact code blocks that couldn't be applied and the differences between the patch and the current file.
  2. Inspect the mac.c file: Open the mac.c file in a text editor and carefully examine the code around the areas where the patch failed. Look for changes in line numbers, code structure, and function definitions.
  3. Adjust the patch: Based on your analysis, modify the patch file to account for the changes in the mac.c file. This might involve changing line numbers, modifying code blocks, or even rewriting parts of the patch.
  4. Test the patch: After making your changes, try applying the patch again to see if it works. You can use the patch command or the OpenWrt build system to test the patch.
  5. Iterate: Patching is often an iterative process. You might need to make multiple adjustments and test the patch repeatedly until it applies successfully.

Seeking Help from the Community

If you're not comfortable updating the patch yourself, don't despair! The OpenWrt community is a valuable resource. You can reach out to other developers and users for help, guidance, and even updated patches.

Here are some ways to seek help from the community:

  • OpenWrt Forums: The OpenWrt forums are a great place to ask questions, share your experiences, and get help from other users and developers.
  • OpenWrt Wiki: The OpenWrt wiki contains a wealth of information about OpenWrt, including troubleshooting guides, development resources, and community contact information.
  • OpenWrt Bug Tracker: If you believe you've found a bug in OpenWrt, you can report it on the OpenWrt bug tracker. This allows developers to track and address issues in a systematic way.

When seeking help, be sure to provide as much information as possible about your setup, the error you're encountering, and the steps you've taken to troubleshoot the issue. The more information you provide, the easier it will be for others to assist you.

Requesting an Updated Patch

In this specific case, it's highly recommended to request an updated version of the 236-003 patch from the patch maintainers or the OpenWrt community. When requesting an updated patch, be sure to provide the following information:

  • Backports Version: Specify the backports version you're using (6.12.52 or later).
  • Patch Name: Identify the patch by its filename (236-003-ath11k-add-dynamic-VLAN-support-in-NSS-offload.patch).
  • Error Output: Include the error output you're seeing, including the rejected hunk information.
  • Context: Explain the context of the issue, such as your OpenWrt version, target device, and build configuration.

By providing this information, you'll make it easier for others to understand the problem and provide an appropriate solution.

Key Questions to Ask

When requesting an updated patch, it's also helpful to ask some key questions:

  1. Correct Backports Version: What is the correct backports version for this patch series?
  2. Maintenance Status: Is dynamic VLAN support in NSS offload still actively maintained?
  3. Updated Patches: Are there updated patches available that are compatible with the current backports version?

These questions will help you understand the current status of the patch and whether there's an official solution available.

Conclusion: Persistence Pays Off

The mac80211 NSS Dynamic VLAN patch failure can be a frustrating issue, but it's not insurmountable. By understanding the root cause, examining the error output, and leveraging the resources of the OpenWrt community, you can overcome this challenge.

Remember, software development is often a process of trial and error. Don't be discouraged by setbacks. Persistence, attention to detail, and a willingness to learn are the keys to success. So, keep digging, keep experimenting, and keep asking questions. You'll get there eventually!

If you have any questions or insights to share, feel free to leave a comment below. Let's work together to make OpenWrt even better!