Re: Cygwin off_t, dev_t, uid_t and gid_t definitions

[Corinna Vinschen <vinschen at redhat dot com>]

On Apr 13 08:18, Sebastian Huber wrote:
> Hello,
> 
> we have currently an exception for Cygwin in the <sys/types.h> header:
> 
> #ifndef __CYGWIN__    /* which defines these types in it's own types.h. */
> typedef _off_t    off_t;
> typedef __dev_t dev_t;
> typedef __uid_t uid_t;
> typedef __gid_t gid_t;
> #endif
> 
> Cygwin defines these types in "winsup/cygwin/include/cygwin/types.h":
> 
> #ifndef __off_t_defined
> #define __off_t_defined
> /* Based on the newlib definitions. */
> #if __WORDSIZE == 64
> typedef _off_t off_t;
> #else
> typedef _off64_t off_t;
> #endif
> #endif /*__off_t_defined*/
> 
> #ifndef __dev_t_defined
> #define __dev_t_defined
> typedef __int16_t __dev16_t;
> typedef __uint32_t dev_t;
> #endif /*__dev_t_defined*/
> 
> #ifndef __uid_t_defined
> #define __uid_t_defined
> typedef unsigned short __uid16_t;
> typedef __uint32_t uid_t;
> #endif /*__uid_t_defined*/
> 
> #ifndef __gid_t_defined
> #define __gid_t_defined
> typedef unsigned short __gid16_t;
> typedef __uint32_t gid_t;
> #endif /*__gid_t_defined*/

The special types __dev16_t, __uid16_t, and __gid16_t are only used
inside Cygwin to make stone-age old Cygwin applications happy.  These
don't even need the #ifndef __foo_defined bracketing, in fact.  We don't
even need them in a public header.

> I think this is misleading since it may conflict with the internal types

Misleading?!?  In how far?

> defined by <sys/_types.h>. Maybe Cygwin should define __dev_t, __uid_t and
> __gid_t in <machine/_types.h> (where to place this file?).

winsup/cygwin/include/machine/

> Since the default _off_t definition is
> 
> #ifndef __off_t_defined
> typedef long _off_t;
> #endif
> 
> The off_t definition could be probably simply
> 
> typedef _off_t off_t;

No.  off_t is always 64 bit on Cygwin.  _off_t is 32 bit on i686 and 64
bit on x86_64.  That's why off_t is defined as _off64_t on i686 Cygwin.
For that reason we're also using the stdio64 functions in i686 Cygwin
while x86_64 Cygwin uses the normal stdio functions.

Inside Cygwin the type _off_t is currently used for the same purposes as
the __dev16_t, ... types, to keep really old executables on i686 happy
which have been compiled before Cygwin's off_t has gone 64 bit.


Corinna

-- 
Corinna Vinschen
Cygwin Maintainer
Red Hat

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