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To: perryh@pluto.rain.com
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Sat, 12 Nov 2011 20:57:03 PST."
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Date: Sun, 13 Nov 2011 10:54:27 +0000
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Cc: tim@kientzle.com, freebsd-arch@freebsd.org
Subject: Re: [PATCH] fadvise(2) system call
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In message <4ebf4e1f.hkNuKvwPEzh2GJhi%perryh@pluto.rain.com>, perryh@pluto.rain
.com writes:
>Warner Losh <imp@bsdimp.com> wrote:

>> >> wrote:
>> >>> ... seek(2) is badly broken on tape drives.
>> >>> It does nothing and doesn't return an error ...
>> >> 
>> >> Honestly, I think we've got bigger problems to worry about
>> >> than whether lseek() works on magnetic tape drives ...
>> > 
>> > True, but failing silently -- doing nothing but not returning an
>> > error -- is a POLA violation.  Those are worth fixing simply on
>> > principle.
>>
>> Early Unix layering made that kinda hard... :(
>
>and yet, it somehow manages to return an error if applied to a pipe.
>There must be some point at which the inode type affects the result.

There is a big difference:  pipes operate at the fdesc level, devices
sit behind what can best be explained as a symlink into a different
name-space, and the cdevsw API does not pass the fdesc offset in.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.