P4 Troubleshooting - Symbolic Link

When working with the P4 tutorials, we can typically run the make run command without issues. However, if we move outside of the tutorial directory, we might find that the make run command stops working, usually due to an error like this:

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Makefile:4: ../../utils/Makefile: No such file or directory
make: *** No rule to make target '../../utils/Makefile'.  Stop

This error indicates that the Makefile cannot be found, so make run fails to execute. To address this, one solution is to use a symbolic link to create the necessary path, allowing the system to locate the required Makefile without altering the existing project structure.

Using Symbolic Links to Fix Makefile Path Issues

By creating a symbolic link, you can point to an existing Makefile and resolve the “file not found” issue. This method is flexible, allowing you to fix path issues while keeping the original project structure intact.

Steps

1. Identify a Valid Makefile Path: First, locate a usable Makefile, typically in a different project directory or a related folder.

2. Navigate to the Target Directory: Enter the directory where the make command expects the file, such as ../../utils/.

3. Create the Symbolic Link: Use the ln -s command to create the symbolic link. Here’s the syntax:

   1	ln -s /path/to/existing/Makefile Makefile

   For example, if the valid Makefile is located at /home/p4/tutorials/utils, you would run:

   1	ln -s /home/p4/tutorials/utils ../../utils

4. Verify the Symbolic Link: After creating the link, use this command to check that it correctly points to the Makefile:

   1	ls -l ../../utils/Makefile

   If successful, Linux will return something like w-r-- 1 ..., confirming that the system has located the file, and you should be able to use make run again.

5. Additional Errors

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   - ERROR! While parsing input runtime configuration: file does not exist /home/p4/Desktop/tutorials/basic/build/basic.p4.p4info.txtpb Configuring switch s2 using P4Runtime with file pod-topo/s2-runtime.json - ERROR! While parsing input runtime configuration: file does not exist /home/p4/Desktop/tutorials/basic/build/basic.p4.p4info.txtpb Configuring switch s3 using P4Runtime with file pod-topo/s3-runtime.json - ERROR! While parsing input runtime configuration: file does not exist /home/p4/Desktop/tutorials/basic/build/basic.p4.p4info.txtpb Configuring switch s4 using P4Runtime with file pod-topo/s4-runtime.json

   This error might stem from a file name or path configuration issue. Here are some solutions to resolve it:

   1. Check and retry the compilation parameters (adjust for your specific P4 program as needed):

   1	p4c-bm2-ss --p4v 16 --p4runtime-files build/basic.p4.p4info.txt -o build/basic.json basic.p4

   2. Update Configuration Files to Use .txt Format: Ensure that all configuration files referencing the p4info file use the .txt extension, updating paths in files like pod-topo/s1-runtime.json to build/basic.p4.p4info.txt.

   3. Rerun make run: Once files are generated, try running make run again to see if the switches configure correctly.

   These steps should address the .txtpb format issues, allowing the compiler to generate the p4runtime files successfully.