Date: Sat, 6 Nov 2004 19:15:13 -0500 (EST) From: Garrett Wollman <wollman@khavrinen.lcs.mit.edu> To: phk@phk.freebsd.dk Cc: arch@FreeBSD.org Subject: Re: Multi-threading access to device drivers. Message-ID: <200411070015.iA70FDxm015465@khavrinen.lcs.mit.edu> In-Reply-To: <10847.1099784360@critter.freebsd.dk>
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In article <10847.1099784360@critter.freebsd.dk> you write: >Assume a process with two threads on two CPUs, both >doing read(fd, buf, len) at the same time. > >Should we let both reads into the driver at the same time ? > >If so, which uio_offset do we hand them ? POSIX is quite clear on the matter: > All of the functions chmod (), close (), fchmod (), fcntl (), fstat > (), ftruncate (), lseek (), open (), read (), readlink (), stat (), > symlink ( ), and write ( ) shall be atomic with respect to each other > in the effects specified in IEEE Std 1003.1-2001 when they operate on > regular files. If two threads each call one of these functions, each > call shall either see all of the specified effects of the other call, > or none of them. (One of the "specified effects" is advancing the file offset.) -GAWollman -- Garrett A. Wollman | As the Constitution endures, persons in every wollman@lcs.mit.edu | generation can invoke its principles in their own Opinions not those of| search for greater freedom. MIT, LCS, CRS, or NSA| - A. Kennedy, Lawrence v. Texas, 539 U.S. ___ (2003)
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