**Gadgetfs Not Mounted After Kernel Build**

Issue Overview

The issue at hand involves users experiencing difficulties with mounting gadgetfs after customizing and building the Jetpack 6 kernel for the Nvidia Jetson Orin Nano. Users report that while the kernel boots successfully, it fails to mount gadgetfs, leading to functionality limitations. Symptoms include:

• Errors: Users encounter messages indicating that gadgetfs is not loaded or recognized as an unknown filesystem.
• Context: The problem arises specifically after modifying kernel configurations related to USB gadget support during the setup process.
• Hardware/Software Specifications: Users are working with Jetpack 6 and the Jetson Orin Nano developer kit, utilizing configurations set in make menuconfig.
• Frequency: This issue appears consistently among users who have altered their kernel settings without successfully enabling gadgetfs.
• Impact: The inability to mount gadgetfs restricts users from utilizing USB gadgets effectively, impacting their projects that rely on USB device emulation.

Possible Causes

Several potential causes for the failure to mount gadgetfs have been identified:

• Kernel Configuration Errors: Incorrect settings in make menuconfig can lead to essential components not being included in the build.
• Module Loading Issues: If the kernel does not load the necessary modules for gadgetfs, it will not function correctly.
• Driver Conflicts: Changes made to driver settings or failing to include required drivers may prevent proper operation.
• Filesystem Type Issues: If the underlying filesystem type is unsupported or misconfigured, mounting will fail.
• Loopback Capability Missing: Removing loopback support can cause issues when attempting to mount files as mass storage gadgets, leading to failure in loading gadgetfs.

Troubleshooting Steps, Solutions & Fixes

To diagnose and resolve the issue with mounting gadgetfs, follow these comprehensive steps:

1. Verify Kernel Configuration:

   • Start with a configuration that matches the original running kernel. Use a context-aware editor like nconfig or menuconfig.
   • Ensure that you have enabled:
     • Device Drivers → USB Support → Gadget Support → GadgetFS
     • Confirm that loopback support is included.

2. Check Kernel Version and Modules:

   • Use the command:

     uname -r
     

   • Ensure that you are booting from the correct kernel version and that it corresponds with the modules in /lib/modules/.

3. Load Required Modules:

   • After booting into your customized kernel, check loaded modules using:

     lsmod
     

   • If gadgetfs is not listed, manually load it using:

     sudo modprobe gadgetfs
     

4. Mount GadgetFS Manually:

   • Attempt to mount gadgetfs using:

     sudo mount -t gadgetfs none /dev/gadget
     

   • If this fails, check for error messages indicating why it could not mount.

5. Rebuild Kernel if Necessary:

   • If issues persist, consider rebuilding the kernel ensuring all necessary configurations are retained. Avoid changing CONFIG_LOCALVERSION unless necessary.

6. Check Filesystem Compatibility:

   • Verify that the underlying storage media (e.g., ext4, VFAT) is compatible with what you are trying to mount through gadgetfs.

7. Consult Documentation and Community Resources:

   • Refer to Nvidia’s official documentation for any updates or specific notes regarding USB gadget support in Jetpack 6.

8. Test Different Configurations:

   • If possible, test different hardware configurations or revert to a previous known working kernel version.

9. Best Practices for Future Prevention:

   • Always maintain a backup of working configurations.
   • Document changes made during kernel customization for easier troubleshooting in future builds.

10. Unresolved Aspects:

    • Further investigation may be needed regarding specific driver dependencies or potential bugs within Jetpack 6 related to gadget support.

By following these steps, users should be able to diagnose and potentially resolve issues related to mounting gadgetfs.