Re: System call v.s. errno

["Måns Rullgård" <mru@inprovide.com>]

"Richard B. Johnson" <linux-os@analogic.com> writes:

> 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.
>
> The answer is not obvious because the 'C' runtime library
> doesn't really give access to 'errno' instead it is dereferenced
> off some pointer returned from a function called __errno_location().

The kernel knows nothing about errno.  Have you tried using strace to
check the actual return values of the system calls?

> This problem does not exist with Linux-2.4.x. It started to show
> up when user's updated their machines to newer RH stuff that uses
> linux-2.6.5-1.358.

So go file a bug with redhat.  It wouldn't be the first time they ship
broken stuff.

-- 
Måns Rullgård
mru@inprovide.com