On Jan 18, 2014, at 11:00 AM, Steve Dickson <SteveD@xxxxxxxxxx> wrote: > On 16/01/14 12:31, Chuck Lever wrote: >> I was reminded recently that NFS treats file atime time stamps >> differently than other filesystems. It also ignores the generic >> *atime mount options because it cannot support the atime semantics >> of local filesystems. >> >> We should document that somewhere. nfs(5) seems like a logical >> place for it. >> >> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx> > I'm a bit confused... What is the different between this patch > and the one you posted back in Nov 18 > http://www.spinics.net/lists/linux-nfs/msg40559.html > which turned to commit > > commit f41c591f8f4d492ee84994bb86810fb90bef8d4b > Author: Chuck Lever <chuck.lever@xxxxxxxxxx> > Date: Wed Nov 20 14:10:06 2013 -0500 I pulled, but didn’t see this one. If you already have it post 1.2.9, you can ignore this patch. > > steved. >> --- >> utils/mount/nfs.man | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 59 insertions(+) >> >> diff --git a/utils/mount/nfs.man b/utils/mount/nfs.man >> index 67031b5..2250963 100644 >> --- a/utils/mount/nfs.man >> +++ b/utils/mount/nfs.man >> @@ -1227,6 +1227,65 @@ If absolute cache coherence among clients is required, >> applications should use file locking. Alternatively, applications >> can also open their files with the O_DIRECT flag >> to disable data caching entirely. >> +.SS "File timestamp maintainence" >> +NFS servers are responsible for managing file and directory timestamps >> +.RB ( atime , >> +.BR ctime ", and" >> +.BR mtime ). >> +When a file is accessed or updated on an NFS server, >> +the file's timestamps are updated just like they would be on a filesystem >> +local to an application. >> +.P >> +NFS clients cache file attributes, including timestamps. >> +A file's timestamps are updated on NFS clients when its attributes >> +are retrieved from the NFS server. >> +Thus there may be some delay before timestamp updates >> +on an NFS server appear to applications on NFS clients. >> +.P >> +To comply with the POSIX filesystem standard, the Linux NFS client >> +relies on NFS servers to keep a file's >> +.B mtime >> +and >> +.B ctime >> +timestamps properly up to date. >> +It does this by flushing local data changes to the server >> +before reporting >> +.B mtime >> +to applications via system calls such as >> +.BR stat (2). >> +.P >> +The Linux client handles >> +.B atime >> +updates more loosely, however. >> +NFS clients maintain good performance by caching data, >> +but that means that application reads, which normally update >> +.BR atime , >> +are not reflected to the server where a file's >> +.B atime >> +is actually maintained. >> +.P >> +Because of this caching behavior, >> +the Linux NFS client does not support generic atime-related mount options. >> +See >> +.BR mount (8) >> +for details on these options. >> +.P >> +In particular, the >> +.BR atime / noatime , >> +.BR diratime / nodiratime , >> +.BR relatime / norelatime , >> +and >> +.BR strictatime / nostrictatime >> +mount options have no effect on NFS mounts. >> +.P >> +.I /proc/mounts >> +may report that the >> +.B relatime >> +mount option is set on NFS mounts, but in fact the >> +.B atime >> +semantics are always as described here, and are not like >> +.B relatime >> +semantics. >> .SS "Directory entry caching" >> The Linux NFS client caches the result of all NFS LOOKUP requests. >> If the requested directory entry exists on the server, >> -- 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
