Date: Thu, 4 Aug 2005 17:57:11 +1000 From: Peter Jeremy <PeterJeremy@optushome.com.au> To: Andrey Chernov <ache@freebsd.org>, Maxim.Sobolev@portaone.com, Dan Nelson <dnelson@allantgroup.com>, "current@freebsd.org" <current@freebsd.org> Subject: Re: Sub-optimal libc's read-ahead buffering behaviour Message-ID: <20050804075711.GB271@cirb503493.alcatel.com.au> In-Reply-To: <20050804063908.GA21871@nagual.pp.ru> References: <42F0CCD5.9090200@portaone.com> <20050803150117.GD93405@dan.emsphone.com> <42F0E9B2.9080208@portaone.com> <20050804060251.GA21228@nagual.pp.ru> <20050804063908.GA21871@nagual.pp.ru>
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On Thu, 2005-Aug-04 10:39:09 +0400, Andrey Chernov wrote: >So (considering changing content like /dev/mem too), any buferization is >potentially dangerous here. fseek traditionally used as buferization >break, in case, say, between fread and fwrite. In case SEEK_CUR still uses >the buffer, it probably should not for character device. I can't see any reason for the current stdio behaviour: - If you're accessing a device with "magic" behaviour then it's not safe to read(2) 4KB (or whatever) when userland asks to fread(3) 512 bytes. - If the device doesn't have "magic" behaviour then you can just seek within the stdio buffer. That said, I've seen similar behaviour on other systems so it could be a subtle side-effect of POSIX. -- Peter Jeremy
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