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Date: Sun, 19 Apr 1998 13:00:06 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199804190300.NAA15945@godzilla.zeta.org.au>
To: cvs-all@FreeBSD.ORG, cvs-committers@FreeBSD.ORG, cvs-lib@FreeBSD.ORG,
        cvs-sys@FreeBSD.ORG, des@FreeBSD.ORG
Subject: Re: cvs commit: src/lib/libc/sys lseek.2 src/sys/kern vfs_syscalls.c
Sender: owner-cvs-sys@FreeBSD.ORG
X-Loop: FreeBSD.org
Precedence: bulk

>des         1998/04/18 12:24:45 PDT
>
>  Modified files:
>    lib/libc/sys         lseek.2 
>  Log:
>  Return EINVAL and do not changefile pointer if resulting offset is negative.
>  PR:		kern/6184
>  
>  Revision  Changes    Path
>  1.7       +2 -2      src/lib/libc/sys/lseek.2
>
>  Modified files:
>    sys/kern             vfs_syscalls.c 
>  Log:
>  Return EINVAL and do not change file pointer if resulting offset is negative.
>  PR:		kern/6184

This is wrong.  Please back it out.  It breaks at least the ability to
seek to high addresses in /dev/[k]mem on 64 bit systems.  Not long ago
when off_t was 32 bits, it was normal to seek to "negative" addresses in
/dev/kmem, so portable programs should be able to handle such addresses
at least if they actually request them.  libkvm/kvm_proc.c:kvm_uread()
shows how to handle them:

	errno = 0;
	if (lseek(fd, (off_t)uva, 0) == -1 && errno != 0) {
		/* Error. */
		...
	}
	/* No error. */
	...

This allows seeking to (off_t)-1 provided the system supports it.

I replied to the PR, but for some reason the followup didn't get attached
to the PR.

Bruce