问题:

I am writing a program consisting of user program and a kernel module. The kernel module needs to gather data that it will then "send" to the user program. This has to be done via a /proc file. Now, I create the file, everything is fine, and spent ages reading the internet for answer and still cannot find one. How do you read/write a /proc file from the kernel space ? The write_proc and read_proc supplied to the procfile are used to read and write data from USER space, whereas I need the module to be able to write the /proc file itself.

回答1:

That's not how it works. When a userspace program opens the files, they are generated on the fly on a case-by-case basis. Most of them are readonly and generated by a common mechanism:

Register an entry with create_proc_read_entry
Supply a callback function (called read_proc by convention) which is called when the file is read
This callback function should populate a supplied buffer and (typically) call proc_calc_metrics to update the file pointer etc supplied to userspace.

You (from the kernel) do not "write" to procfs files, you supply the results dynamically when userspace requests them.

回答2:

One of the approaches to get data across to the user space would be seq_files. In order to configure (write) kernel parameters you may want to consider sys-fs nodes.

Thanks, Vijay