Re: Problem with autounload of nfsserver module

[Paul Goyette <paul%whooppee.com@localhost>]

On Sat, 14 Dec 2013, Christos Zoulas wrote:

> In article <Pine.NEB.4.64.1312140541170.819%screamer.whooppee.com@localhost>,
> Paul Goyette  <paul%whooppee.com@localhost> wrote:
> > I believe that the nfsserver module should not be allowed to autounload.
> >
> > Consider the following sequence of events:
> >
> > 1. mountd is started, and calls nfssvc(2)
> > 2. The module subsystem autoloads the nfsserver module
> > 3. mountd continues, adding entries to the exports list
> >
> > So far, everything is fine.  However....
> >
> > 4. When the autounload timer expires, the module subsystem unloads the
> >    nfsserver module
> > 5. As part of nfsserver_modcmd(), the export list is cleared
> > 6. The autounload completes successfully
> > 7. At some later time, we finally get around to starting nfsd.  This
> >    succeeds, but the export list has been cleared, so there is nothing
> >    for nfsd to deliver to the clients.
> >
> > So, depending on how much time it takes between starting mountd and
> > starting nfsd, we could end up serving an empty exports list.
> >
> > The following patch prevents the module subsystem from unloading the
> > nfsserver module.  (Manual unloading of the module will still work.)
> > Comments?
>
> Perhaps you want it to prevent it from unloading while there are exported
> filesystems?

Yeah, that would work, too.  :)   The following patch prevents the 
module from being auto-unloaded if there are exported filesystems.  (If 
a manual unload is requested, we will still forcibly delete the exports 
list.)


Index: nfs_export.c
===================================================================
RCS file: /cvsroot/src/sys/nfs/nfs_export.c,v
retrieving revision 1.57
diff -u -p -r1.57 nfs_export.c
--- nfs_export.c        23 Nov 2013 14:20:46 -0000      1.57
+++ nfs_export.c        14 Dec 2013 15:06:47 -0000
@@ -225,6 +225,13 @@ netexport_fini(void)
        rw_destroy(&netexport_lock);
 }

+int
+netexport_listempty(void)
+{
+
+       return TAILQ_EMPTY(&netexport_list);
+}
+

 /*
  * Atomically set the NFS exports list of the given file system, replacing
Index: nfs_serv.c
===================================================================
RCS file: /cvsroot/src/sys/nfs/nfs_serv.c,v
retrieving revision 1.166
diff -u -p -r1.166 nfs_serv.c
--- nfs_serv.c  14 Sep 2013 22:29:08 -0000      1.166
+++ nfs_serv.c  14 Dec 2013 15:06:47 -0000
@@ -144,6 +144,11 @@ nfsserver_modcmd(modcmd_t cmd, void *arg
                nfsrv_finicache();
                nfs_fini();
                return 0;
+       case MODULE_CMD_AUTOUNLOAD:
+               /* Don't allow auto-unload if there are any exports */
+               if (!netexport_listempty())
+                       return EBUSY;
+               /* FALLTHROUGH */
        default:
                return ENOTTY;
        }
Index: nfs_var.h
===================================================================
RCS file: /cvsroot/src/sys/nfs/nfs_var.h,v
retrieving revision 1.90
diff -u -p -r1.90 nfs_var.h
--- nfs_var.h   2 Mar 2010 23:19:09 -0000       1.90
+++ nfs_var.h   14 Dec 2013 15:06:47 -0000
@@ -349,4 +349,5 @@ void netexport_rdlock(void);
 void netexport_rdunlock(void);
 void netexport_init(void);
 void netexport_fini(void);
+int netexport_listempty(void);
 #endif /* _KERNEL */


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