Re: System call v.s. errno

[Stephen Hemminger <shemminger@osdl.org>]

On Wed, 4 May 2005 09:49:37 -0400 (EDT)
"Richard B. Johnson" <linux-os@analogic.com> wrote:

> On Wed, 4 May 2005, Jakub Jelinek wrote:
> 
> > On Wed, May 04, 2005 at 09:22:09AM -0400, Richard B. Johnson wrote:
> >> Does anybody know for sure if global 'errno' is supposed to
> >> be altered after a successful system call? I'm trying to
> >> track down a problem where system calls return with EINTR
> >> even though all signal handlers are set with SA_RESTART in
> >> the flags. It appears as though there may be a race somewhere
> >> because if I directly set errno to 0x1234, within a few
> >> hundred system calls, it gets set to EINTR even though all
> >> system calls seemed to return 'good'. This makes it
> >> hard to trace down the real problem.
> >
> > http://www.opengroup.org/onlinepubs/009695399/functions/errno.html
> > is very clear on this.  Unless indicated that errno is valid after a call
> > (for many syscalls it is valid when the syscall returns -1), errno has
> > unspecified value.
> >
> > 	Jakub
> > -
> 
> Okay, thanks. That means that it's okay for it to get trashed
> NotGood(tm) for debugging.
> 
> Cheers,
> Dick Johnson

Also, on with NPTL and many thread libraries errno is really a macro
that refers to a per-thread variable.

-- 
Stephen Hemminger	<shemminger@osdl.org>