Date: Mon, 10 Mar 2003 10:13:36 -0800 (PST) From: Nate Lawson <nate@root.org> To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: cvs-src@FreeBSD.org, src-committers@FreeBSD.org Subject: Re: cvs commit: src/sys/sys devicestat.h Message-ID: <Pine.BSF.4.21.0303101009420.93727-100000@root.org> In-Reply-To: <2856.1047319447@critter.freebsd.dk>
next in thread | previous in thread | raw e-mail | index | archive | help
On Mon, 10 Mar 2003, Poul-Henning Kamp wrote: > In message <Pine.BSF.4.21.0303100924470.93706-100000@root.org>, Nate Lawson wri > tes: > >I'm unsure why two counters are required. One counter at the start of the > >structure is sufficient if you 1. memcpy the structure and then 2. re-read > >the counter int to make sure it is the same as the one covered by the > >memcpy. (This assumes memcpy can read an int atomically which should be > >true). Hmm, a volatile keyword may be necessary for the user-visible > >struct. > > Think two cpu system. > > One cpu doing the memcpy in userland while the other is updating the > data structure in the kernel. This changes nothing about my suggestion as long as you always update the sequence before changing the structure in the kernel. -Nate To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-src" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?Pine.BSF.4.21.0303101009420.93727-100000>