Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!execu!sequoia!rpp386!jfh
From: jfh@rpp386.cactus.org (John F. Haugh II)
Newsgroups: comp.unix.wizards
Subject: Re: Anything faster than stat(S)? need to determine File or Dir
Message-ID: <17272@rpp386.cactus.org>
Date: 11 Nov 89 18:06:52 GMT
References: <152@norsat.UUCP> <2586@unisoft.UUCP> <15769@bloom-beacon.MIT.EDU> <17264@rpp386.cactus.org> <1989Nov11.154312.6675@virtech.uucp>
Reply-To: jfh@rpp386.cactus.org (John F. Haugh II)
Organization: Lone Star Cafe and BBS Service
Lines: 33

In article <1989Nov11.154312.6675@virtech.uucp> cpcahil@virtech.uucp (Conor P. Cahill) writes:
>So you want to replace a single call to stat() with multiple calls to 
>access().  That doesn't make any sense since the major overhead to both
>the stat and access system calls is that the path must be traversed and since
>you are calling access twice, you have to traverse the path twice.

The objective was to take advantage of path-name caching on BSD systems.

Of course, if you know "/path/name" exists, you only need -one- call
to access() with "/path/name/foo" and you save the mumbo-jumbo required
to get data from kernel to user space.

>stat() is the most effecient mechanism that can be used to obtain information
>about a file system entry since it just looks up an inode and copies
>the data to the user's data area.

Probably true.  Now, go off and actually run the benchmarks.  =Always=
question everything.  On some machines copies from system to user address
space are cheap.  On others it can be =very= difficult.  There is a big
difference between a Vax where the supervisor and user have separate
address spaces which can be directly addressed one from the other, and a
PDP-11 where the supervisor and user occupy the same address space and
have no [ MTPD and MFPD aren't implemented on all PDP-11 CPUs! ] easy
way of communicating short of mapping memory all over God's creation.

Anyway, it was only meant to stimulate discussion.  The only portable
and clean solution =is= to use stat().  I can't stand clever hacks,
unless I write them myself ;-)
-- 
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