On Mar. 19, 2009, 18:43 +0200, Chuck Lever <chuck.lever@xxxxxxxxxx> wrote: > On Mar 19, 2009, at Mar 19, 2009, 12:34 PM, Muntz, Daniel wrote: >>> -----Original Message----- >>> From: Steve Dickson [mailto:SteveD@xxxxxxxxxx] >>> Sent: Thursday, March 19, 2009 9:18 AM >>> To: linux NFS Mailing list >>> Subject: The next step: nfsvers=4 >>> >>> As I see it, the next step to seamlessly move to V4 as the >>> default is to make 'mount -o nfsvers=4' actually do a v4 mount... >>> >>> There are two obvious place we can make this change. >>> In the kernel and/or in the mount command... >>> >>> Looking at the kernel, since v3 and v4 truly two different >>> file systems its seems a bit late for the nfs_get_sb() to all >>> of sudden have to change file system type. Meaning when >>> nfs_get_sb() sees the "nfsvers=4" somehow it would have to >>> back out and call nfs4_get_sb(), which obviously is a bit hacky.... >>> >>> Now I guess we could have one nfs_get_sb() for both v3 and v4. >>> Where the nfs_get_sb() could peek into the options data to >>> see which version is needed. This would also mean the mount >>> command would always have to set a version so when the "nfsvers=" >>> options is not set, the kernel would know which version to use. >>> Again, this feels a bit hacky as well but doable... >>> >>> At least to me, what seems like the best option is to have >>> the mount.nfs binary early on intercept "nfsvers=4" option >>> and then change the fs_type to "nfs4", which would allow >>> everything to "trickle down" as it does today... Again to me, >>> that seem like the least intrusive way to do it... >>> >>> Comments? Is there other ways? > > Having the mount.nfs command translate sounds like a pretty easy thing > to prototype. > >> Whichever way it's done, if v4 becomes the default, don't forget to >> also >> make the default behavior be that the system will fall back and try >> a v3 >> mount if v4 isn't available. Otherwise you'll break a huge percentage >> of your user base. Of course then you also have to deal with the >> semantics of how to specifify "only v4" vs. "try v4 first and fall >> back". > > Today, specifying vers=3 means "I want vers=3 or nothing". Not > specifying any version means the mount command can choose which > version to use based on what both sides support. > > If no vers= option is specified, I don't think it would be difficult > for the text-based mount command to try a "nfs4" mount first, and if > that fails try an "nfs" mount. Agreed. That's pretty much what we planned to do in the future also for minorversion=1, after discussing this also with Trond. The principle was that the policy for choosing what versions to try and in which order should be determined by the user mode utilities since one can think of customers that would only want to use nfsv4.1 for its exactly once semantics, or others that would want to start with 4.0 and fall back to 3 and 2 since trying 4.1 might break their servers, etc. I think that if no version is specified all versions that the client supports should be tried, highest first. Otherwise mount.nfs should try only the specified version. For implementing more complex policies, maybe we can extend the command syntax to accept a range and/or an ordered list of versions to try. Benny > > Steve, would you like me to provide a prototype mount.nfs command that > handles this? > > -- > Chuck Lever > chuck[dot]lever[at]oracle[dot]com > -- > To unsubscribe from this list: send the line "unsubscribe linux-nfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
