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.
2 Answers
8
votes
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.
