[PATCH] Use vfs_timestamp() instead of getnanotime() in NFS

[Bruce Evans]

On Thu, 17 Jan 2013, Rick Macklem wrote:

> John Baldwin wrote:
>> On Tuesday, January 15, 2013 2:58:42 pm John Baldwin wrote:
>>> Fixing NFS to properly use vfs_timestamp() seems to be a larger
>>> project.
>>
>> Actually, I have a patch that I think does this below. It builds, have
>> not
>> yet booted it (but will do so in a bit).
>>
>> Index: fs/nfsclient/nfs_clstate.c
>> ===================================================================
>> --- fs/nfsclient/nfs_clstate.c (revision 245225)
>> +++ fs/nfsclient/nfs_clstate.c (working copy)
>> @@ -4611,7 +4611,7 @@
>> }
>> dp = nfscl_finddeleg(clp, np->n_fhp->nfh_fh, np->n_fhp->nfh_len);
>> if (dp != NULL && (dp->nfsdl_flags & NFSCLDL_WRITE)) {
>> - NFSGETNANOTIME(&dp->nfsdl_modtime);
>> + vfs_timestamp(&dp->nfsdl_modtime);
>> dp->nfsdl_flags |= NFSCLDL_MODTIMESET;
>> }
>> NFSUNLOCKCLSTATE();
> Not sure about this case. Although nfsdl_modtime is being set for local
> use, it replaces the mtime returned by the NFS server while the delegation
> is in use. Ideally it would be the same resolution as the NFS server, but
> that resolution isn't known to the client. (It is often better than 1sec,
> which is the default for vfs_timestamp().)

The patch seems about right except for this.

> I'd be tempted to leave it (although the function used by the macro might
> need to be changed, since Bruce mentions getnanotime() isn't supposed to
> be used?).

For maximal precision and accuracy, it nanotime() should be used.  I'm
not sure if you need to be at least as precise and accurate as the server.
Having them synced to nanoseconds accuracy is impossible, but
getnanotime() gives <= 1/HZ of accuracy and it is easy for them to be
synced with more accuracy than that.  Then the extra accuracy can be
seen in server timestamps if the server is FreeBSD and uses vfs_timestamp()
with a either microtime() or nanotime().

Further style fixes:
- remove the NFSGETNANOTIME() macro.  It is only used in the above, and
   in 3 other instances where its use is bogus because only the seconds
   part is used.  The `time_second' global gives seconds part with the
   same (in)accuracy as getnanotime().  If you want maximal accuracy
   for just the seconds part, then bintime() should be used (this is
   slightly faster than microtime() and nanotime().
     (get*time()'s seconds part is the same as time_second.  This
     inaccurate since it lags bintime()'s seconds part by up to 1/HZ
     seconds (so it differs by a full second for an everage of 1 one
     in every HZ readings).  The difference is visible if one reader,
     say make(1) reads the time using bintime() while another reader,
     say vfs_timestamp() reads the time using getbintime().)

>> Index: nfsserver/nfs_srvsubs.c
>> ===================================================================
>> --- nfsserver/nfs_srvsubs.c (revision 245225)
>> +++ nfsserver/nfs_srvsubs.c (working copy)
>> @@ -1393,7 +1393,7 @@
>> toclient = 1;
>> break;
>> case NFSV3SATTRTIME_TOSERVER:
>> - getnanotime(&(a)->va_atime);
>> + vfs_timestamp(&(a)->va_atime);
>> a->va_vaflags |= VA_UTIMES_NULL;
>> break;
>> }
>> @@ -1409,7 +1409,7 @@
>> a->va_vaflags &= ~VA_UTIMES_NULL;
>> break;
>> case NFSV3SATTRTIME_TOSERVER:
>> - getnanotime(&(a)->va_mtime);
>> + vfs_timestamp(&(a)->va_mtime);
>> if (toclient == 0)
>> a->va_vaflags |= VA_UTIMES_NULL;
>> break;

- parenthesizing 'a' is bogus.

Bruce