isatty()

[Jeff Johnston]

Vincent Rivière wrote:
> Hello.
>
> I see in the sources that isatty() is not handled as the other syscalls:
> - there is no _isatty_r() in reent
> - there is no _isatty() at all
> - there is no isatty() in syscalls
> - libgloss implements directly isatty(), not _isatty()
>
> There is the usual errno problem:
> For example, the implementation of isatty() in libnosys fills "extern 
> int errno", but the user applications will read __errno_r(_REENT) 
> instead. Usually, the errno translation occurs in the _r function, but 
> in this case, the _r function does not exist.
>
> However, this is not a big issue, because errno is rarely read after 
> calling isatty().
>
> Is there a reason for the spacial handling of isatty() ?
>
_isatty is not one of the fundamental syscalls required by newlib.  
Remember that newlib's historical origin was to support embedded 
platforms and it only required a small set of syscalls to support the 
ANSI C plus miscellaneous functions.  There is a rough isatty() 
implementation in libc/posix that uses fstat, not _isatty.

Platforms that have wanted it have typically just done so directly in 
their libgloss implementation or libc/sys (used before libgloss was 
created) or they use the libc/posix implementation or they use the 
default libgloss/isatty.c version (always returns 1) or they let 
libnosys resolve it (always returns 0) just to allow tests to link/run.

-- Jeff J.

-- Jeff J.