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I've implemented a few custom system calls in my Ubuntu kernel, but I'm having some issues with the return values. Each function returns a variety of non-negative integers depending on ...
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  1. #1
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    Return values from system calls


    I've implemented a few custom system calls in my Ubuntu kernel, but I'm having some issues with the return values. Each function returns a variety of non-negative integers depending on which error is encountered. However, when I'm testing the system calls, the only negative value that gets returned to the user program is -1, regardless of what I have in the code.

    Is there some special path I have to take to get the proper return values?

    Thanks.

  2. #2
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    I'm having the exact same problem. This wouldn't be for a school project would it?

    I have verified that the code returning other negative values is getting executed by placing printk()'s before those return statements.

    Yet the -1 is all I can get.

    EDIT: I may have solved this. I've looked into errno. I may be wrong about this, but I think the calls will only return -1 specifying that an error has occurred, then the caller must check errno to see what error that was.
    Last edited by ragnaroktomorrow; 04-30-2011 at 02:56 AM.

  3. #3
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    No, it's not for a school project.

    I thought that it might be an errno issue, but I've only recently started tinkering with linux under the hood. Do I have to explicitly set errno in the system call? Or will a negative value jump into it automatically?

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  5. #4
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    Quote Originally Posted by Fewmitz View Post
    Or will a negative value jump into it automatically?
    I believe so yes, but it won't be negative.

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