Date: Fri, 18 Nov 2011 12:00:07 -0800 From: Tim Kientzle <tim@kientzle.com> To: Juergen Lock <nox@jelal.kn-bremen.de> Cc: Alexander Best <arundel@freebsd.org>, freebsd-hackers@freebsd.org Subject: Re: easy way to determine if a stream or fd is seekable Message-ID: <B06B2304-A1BC-49A3-A811-F05625138D58@kientzle.com> In-Reply-To: <201111172055.pAHKtZso061118@triton8.kn-bremen.de> References: <20111115202450.GA73512@freebsd.org> <20111116102239.GA2687@britannica.bec.de> <20111116131428.GA40723@freebsd.org> <20111116232152.GC21793@britannica.bec.de> <20111117002438.GA55931@freebsd.org> <201111172055.pAHKtZso061118@triton8.kn-bremen.de>
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On Nov 17, 2011, at 12:55 PM, Juergen Lock wrote: >>=20 >> After a few experiments, bsdtar stopped using lseek() on >> FreeBSD for anything other than regular files and block >> devices. I believe there are other things that do support >> seeking, but I don't believe there is an accurate mechanism >> for determining whether lseek() is correctly supported. >=20 > Ah is that the reason why my patch never made it into FreeBSD 9? > I'm talking about this thread, where I also commented on seeking > on tape: >=20 > http://docs.freebsd.org/cgi/mid.cgi?20100220101724.GA26604 > (Re: "tar tfv /dev/cd0" speedup patch) >=20 > entire thread here: > http://markmail.org/message/nfznipqik3tuhbqp >=20 > Cheers, > Juergen (who would still like to see a faster "tar tfv = /dev/cd0"... :) I would like to see that as well. Take a look at=20 = http://libarchive.googlecode.com/svn/trunk/libarchive/archive_read_open_fi= lename.c Especially the comments about detecting "disk-like" devices. I rewrote a bunch of this code to introduce an explicit notion of "strategy" so that we could optimize access to a variety of different devices. This code has a notion of "disk-like" file descriptors and some optimizations for such. There are some comments in there outlining similar optimizations that could be made for "tape-like" or "socket-like" devices. Cheers, Tim
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