[PATCH 0/4] typesafe callbacks - Kernel

This is a discussion on [PATCH 0/4] typesafe callbacks - Kernel ; It's possible to portably make callbacks typesafe, as well as taking the existing void * arg. This makes the callers more readable and more typesafe. Done in a way that doesn't break non-gcc: they just don't get a warning. Been ...

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  1. [PATCH 0/4] typesafe callbacks

    It's possible to portably make callbacks typesafe, as well as taking the
    existing void * arg. This makes the callers more readable and more typesafe.

    Done in a way that doesn't break non-gcc: they just don't get a warning.

    Been in linux-next for about two full cycles now, and I really want to start
    using this in my own code.

    Thanks,
    Rusty.
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  2. [PATCH 1/4] typesafe: cast_if_type: allow macros functions which take more than one type.

    To create functions which can take two types, but still warn on any
    other types, we need a way of casting one type and no others.

    To make things more complex, it should correctly handle function args,
    NULL, and be usable in initializers. __builtin_choose_expr was
    introduced in gcc 3.1 (kernel needs >= 3.2 anyway).

    (includes Harvey Harrison 's sparse fix)

    Signed-off-by: Rusty Russell
    Cc: Harvey Harrison
    ---
    include/linux/compiler-gcc.h | 18 ++++++++++++++++++
    include/linux/compiler-intel.h | 2 ++
    2 files changed, 20 insertions(+)

    diff -r ecbc022961d8 include/linux/compiler-gcc.h
    --- a/include/linux/compiler-gcc.h Mon Jul 14 12:30:35 2008 +1000
    +++ b/include/linux/compiler-gcc.h Mon Jul 14 20:46:23 2008 +1000
    @@ -61,3 +61,21 @@
    #define noinline __attribute__((noinline))
    #define __attribute_const__ __attribute__((__const__))
    #define __maybe_unused __attribute__((unused))
    +
    +/**
    + * cast_if_type - allow an alternate type
    + * @expr: the expression to optionally cast
    + * @oktype: the type to allow.
    + * @desttype: the type to cast to.
    + *
    + * This is used to accept a particular alternate type for an expression:
    + * because any other types will not be cast, they will cause a warning as
    + * normal.
    + *
    + * Note that the unnecessary trinary forces functions to devolve into
    + * function pointers as users expect, but means @expr must be a pointer or
    + * integer.
    + */
    +#define cast_if_type(expr, oktype, desttype) __builtin_choose_expr( \
    + __builtin_types_compatible_p(typeof(1?(expr)expr)), oktype), \
    + (desttype)(expr), (expr))
    diff -r ecbc022961d8 include/linux/compiler-intel.h
    --- a/include/linux/compiler-intel.h Mon Jul 14 12:30:35 2008 +1000
    +++ b/include/linux/compiler-intel.h Mon Jul 14 20:46:23 2008 +1000
    @@ -29,3 +29,5 @@
    #endif

    #define uninitialized_var(x) x
    +
    +#define cast_if_type(expr, oktype, desttype) ((desttype)(expr))
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