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Date: Tue, 10 Oct 2017 20:51:17 +0200
From: Jens Gustedt <>
To: William Pitcock <>
Subject: Re: [PATCH] stdio: implement fopencookie(3)

Hello William,

On Tue, 10 Oct 2017 18:03:56 +0000 William Pitcock
<> wrote:

> The fopencookie(3) function allows the programmer to create a custom
> stdio implementation, using four hook functions which operate on a
> "cookie" data type.

I know it is not your fault, but the naming conventions in this new
interface are realy bad design.

> +typedef struct {
> +	ssize_t (*read)(void *cookie, char *buf, size_t size);
> +	ssize_t (*write)(void *cookie, const char *buf, size_t size);
> +	int (*seek)(void *cookie, off_t *offset, int whence);
> +	int (*close)(void *cookie);
> +} cookie_io_functions_t;

> +FILE *fopencookie(void *cookie, const char *mode, cookie_io_functions_t io_funcs);

The members may clash with macro names. E.g an implementation would be
allowed to overload "close" with a macro. This is not possible if the
implementation would want to use this interface here at the same time.

User code could legitimately want to use a macro "seek" for its own

Could you at least avoid to use user-space names as function
parameters? Here you should just omit cookie, buf, size, offset,
whence, mode and io_funcs. I think in musl parameters in prototypes
usually don't have names. If you think that we should have them (they
sort of document the interface) you should put them into a reserved
namespace with leading underscore or so, or at least prefix them with


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