On Jan 4, 2008 10:41 PM, Trond Myklebust <[EMAIL PROTECTED]> wrote: > > > On Thu, 2008-01-03 at 11:10 +0100, Michael Kerrisk wrote: > > Hi Trond, > > > > Trond Myklebust wrote: > > > On Wed, 2008-01-02 at 10:55 +0100, Michael Kerrisk wrote: > > >> Hey Trond, > > >> > > >> Would you take a quick look at > > >> > > >> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=453946 > > >> > > >> Do you have some insights on this? What should the man page say about > > >> current support of O_EXCL on NFS? > > >> > > >> Cheers, > > >> > > >> Michael > > > > > > Hi Michael, > > > > > > Timo is correct. O_EXCL has been supported for NFSv3 (and NFSv4) ever > > > since the 2.6 series kernels came out. > > > > > > However, please note that > > > * it is not supported for any 2.4.x kernels, since that would > > > require some VFS re-engineering that is not compatible with the > > > 'stable kernel' rules. > > > * As Timo states, the NFSv2 protocol cannot support O_EXCL > > > semantics. > > > > Thanks. I've rewritten the text as shown below. > > > > I also have another question: is O_APPEND supported in NFSv3 or NFSv4? > > > > > I think the second point warrants keeping the link() workaround mention, > > > though, since people who are interested in writing completely portable > > > software may still find it useful. For instance, a lot of mail delivery > > > setups are still using the type of locking scheme described there. > > > > Yes, that makes sense. > > > > For man-pages-2.75, I rewrote the paragraph as shown here. Could you > > confirm that this is okay? > > > > O_EXCL is not supported on NFS file systems before > > NFSv3 or on Linux before kernel 2.6; it is sup- > > I'd probably just say 'not supported on NFSv2'. There is not NFSv1, so > this would be quite unambiguous. > > > ported on Linux 2.6 and later, with NFSv3 or > > later. In environments where NFS O_EXCL support > > is not provided, programs that rely on it for per- > > forming locking tasks will contain a race condi- > > tion. Portable programs that want to perform > > atomic file locking using a lockfile, and need to > > avoid reliance on NFS support for O_EXCL, can cre- > > ate a unique file on the same file system (e.g., > > incorporating hostname and PID), and use link(2) > > to make a link to the lockfile. If link(2) > > returns 0, the lock is successful. Otherwise, use > > stat(2) on the unique file to check if its link > > count has increased to 2, in which case the lock > > is also successful. > > Looks good otherwise.
Thanks Trond -- I'll make the changes you suggest. I think you missed my question on O_APPEND though? Cheers, Michael -- Michael Kerrisk Maintainer of the Linux man-pages project http://www.kernel.org/doc/man-pages/ Want to report a man-pages bug? Look here: http://www.kernel.org/doc/man-pages/reporting_bugs.html -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
