Re: Delays on "first" access to a NFS mount

["J. Bruce Fields" <bfields@fieldses.org>]

On Wed, Mar 07, 2007 at 10:46:24PM +0100, Simon Peter wrote:
> > 	  Though there's one point I'm unclear on: are the directories
> > 	  you're exporting mountpoints?  That's the normal
> 
> Not all of my exported directories are mountpoints of the underlying
> VFS of the server.

I'd be curious why.  There's some hard-to-solve security problems
there--people can guess filehandles of unexported files and access them
directly without lookups.  So some day I'd love to actually forbid (or
at least strongly discourage) what you're doing....  But clearly we'd
first need to understand why people do that and make sure there are
adequate alternatives.

> Some are, though.

Are the spinning-up delays happening only on those drives that have
exported directories that aren't mountpoints?

> > 	- the filehandle->export mapping that this function tells the
> > 	  kernel about is cached by nfsd for a half-hour.  That time
> > is set a little later in nfsd_fh:
> > 	  I don't think there would be any harm to just changing that
> > 	  time(0)+30*60 to 0x7FFFFFFF (== never expire)--nfs-utils
> > 	  should be invalidating that cache explicitly whenever it's
> > 	  needed.  Maybe that should be the default.
> 
> I could try that for now.
> 
> Are you sure these are invalidated automatically, especially through
> nfs-utils? If the kernel cache never expires, it should consequently
> never ask for it, so nfs-utils would not be involved. Am I missing
> something?

There's also a mechanism by which nfs-utils can ask for the whole cache
to be flushed immediately on its own.  So re-running exportfs to change
the exports, for example, should result in the cache being flushed.  I
haven't checked whether that's done in all the places it should be, but
it probably is.

--b.

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