Re: [NFS] [PATCH] NFS server does not update mtime on setattr request

[Trond Myklebust <trond.myklebust@fys.uio.no>]

On Wed, 2006-06-07 at 11:26 -0400, Peter Staubach wrote:
> J. Bruce Fields wrote:
> 
> >On Wed, Jun 07, 2006 at 10:44:50AM -0400, Peter Staubach wrote:
> >  
> >
> >>I saw that wording too and assumed what I think that you assumed.  I
> >>assumed that that meant that if the new size is equal to the old size,
> >>then nothing should be changed.  However, that does not seem to be how
> >>those words are to be interpreted.  They are to be interpreted as "if
> >>the new length of the file can be successfully set, then the
> >>mtime/ctime should be changed".
> >>    
> >>
> >
> >What's the basis for that interpretation?  The language seems extremely
> >clear:
> >
> >	"On successful completion, if the file size is changed, these
> >	functions will mark for update the st_ctime and st_mtime fields
> >	of the file, and if the file is a regular file, the S_ISUID and
> >	S_ISGID bits of the file mode may be cleared."
> >
> >Why are you concerned about this?  Do you have an actual application
> >that breaks?
> >
> 
> Yes, there is a customer who is quite unhappy that the semantics over Linux
> client NFS are different than those of BSD, Solaris, and local file system
> access on Linux itself.  The basis for my work is based on a bugzilla from
> this customer.
> 
> My interpretation is based on looking at the local behavior on Linux, which
> changes mtime/ctime even if the file size does not change, and SunOS, which
> changes mtime/ctime even if the file size does not change and is very
> heavily SUSv3 compliant.
> 
> In this case, "changed" does not mean "made different".  It simply means
> that the file size is set to the new value.
> 
> I would have chosen different words or a different interpretation too,
> but all of the evidence suggests that the semantics are as I stated.

We've already fixed this to be SuSv3 compliant for both create and
truncate. Your "safe" suggestion would break truncate again. That is why
it is being vetoed.

Cheers,
  Trond