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Subject: Re: [Qemu-devel] [6324] Return -errno on write failure (Gleb Natapov)
From: "=?utf-8?q?Fran=C3=A7ois?= Revol" <revol@free.fr>
Date: Thu, 15 Jan 2009 22:20:33 +0100 CET
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To: qemu-devel@nongnu.org

> Revision: 6324
>           http://svn.sv.gnu.org/viewvc/=3Fview=3Drev&root=3Dqemu&revision=3D6324
> > Author:   aliguori
> Date:     2009-01-15 20:44:26 +0000 (Thu, 15 Jan 2009)
> 
> Log Message:
> -----------
> Return -errno on write failure (Gleb Natapov)

Nooooooooooo
Please do not this bad broken Unix habit!
errno and E* are negative in BeOS and Haiku and sometimes =3D to 
INT32=5FMIN which means negating it results in positive values or even 
overflows.

I've already had too many apps to fix for this.

If you want to know why this violates standards, use IPOT and ask Be, 
Inc. But it's not gonna change soon. And also ask Opengroup why they 
changed their mind later on after only requiring them to be !=3D0. Shame 
on them.

It's IMO much cleaner and logical after seeing many misplaced signs in 
various software on that, but I don't expect to change it on Unix 
anyway, I just ask our way be respected as well.

If you really want to pass the error this way, at least make sure they 
are signed correctly.
See http://svn.ffmpeg.org/ffmpeg/trunk/libavcodec/avcodec.h=3Frevision=3D16580&view=3Dmarkup

#if EINVAL > 0
#define QERROR(e) (-(e)) /**< Returns a negative error code from a 
POSIX error code, to return from library functions. */
#define QUNERROR(e) (-(e)) /**< Returns a POSIX error code from a 
library function error return value. */
#else
/* Some platforms have E* and errno already negated. */
#define QERROR(e) (e)
#define QUNERROR(e) (e)
#endif

and return QERROR(errno) or return QERROR(EINVAL);

This has been used in FFmpeg and many other things and works very well.

In OSS4 they chose to define their own error codes from E* at configure 
time, but I find it more intrusive.

Fran=C3=A7ois.