How many times can you use copy_to_user() in a kernel program?
As many times as you want. But they have to make sense (because anything you do in any kind of program has to make sense).
I thought if the data that is passed into the copy_to_user() will append the data to the next line.
No, copy_to_user does not append anything. I’m not sure where you got that idea.
What is actually happening
Well, you’re copying the data for the first process, then overwriting it with the data for the second process, then overwriting that with the data for the third process, and so on. At the end you’re left with the third process’s data.
How do transfer all three lines to the user space from the kernel space?
Store the data for each process at a different location.
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solved How to use copy_to_user() in a kernel program? [closed]