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    SubjectRe: [PATCH 3/7] drivers: usb: Include appropriate header file in hcd.h
    Hello.

    On 12/19/2013 07:48 PM, Alan Stern wrote:

    >>> Of course, people have varying opinions on this issue. As far as I
    >>> know, there is no fixed policy in the kernel about nested includes.

    >> True. I personally prefer the policy of making all headers
    >> self-contained, and then only including headers that define things used
    >> in the source file. That has the advantage of not including any
    >> unnecessary headers if the dependencies shrink, and not requiring
    >> changes to multiple source files if the dependencies grow.

    >> Any particular objection to making the headers self-contained?

    > I guess it depends on what you mean by "self-contained". The only
    > reasonable definition I can think of at the moment is that you don't
    > get any errors or warnings when you compile the .h file by itself.

    > But what use is that in practice? Nobody ever compiles .h files by
    > themselves.

    It's enough to verify that a .c file containing the given .h file would
    not cause errors *located in that .h file*. This is not really such an
    improbable situation, e.g. at the early stages of development. I did discover
    header fiel errors this way.

    > For that matter, how can you tell that you are including only headers
    > that define things used in the source file?

    I still think that's a whole different issue.

    > Remove each #include line,
    > one at a time, and see if you then get an error? Do you do this after
    > each change to the source file to make sure it remains true over time?

    That's what #include cleanup patches are for. Somebody has to do them from
    time to time when the #include's accumulate -- they tend to accumulate as
    people often forget to remove no longer needed one while removing some feature
    from the .c file.

    > My point is that the C language design and compiler infrastructure make
    > it virtually impossible to enforce any fixed policy.

    I don't really see how C language design can justify header files that
    once included, require each .c file to #include other headers ahead of them,
    each time such header is used. In my opinion, it's just crazy.

    > Alan Stern

    WBR, Sergei



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