DragonFlyBSD

Simon,

I've checked FBSD and NBSD. The former can only do update mounts for NFS exports
it seems, and the latter can't at all.

Any hit for doing this?

Cheers,
Antonio Huete

:Antonio Huete Jimenez <tuxillo@quantumachine.net> added the comment:
:
:Simon,
:
:I've checked FBSD and NBSD. The former can only do update mounts for NFS ex=
:ports
:it seems, and the latter can't at all.
:
:Any hit for doing this?
:
:Cheers,
:Antonio Huete
:
:----------
:status: unread -> chatting

hit -> hint I assume.  Yes, you should be able to imlement the
    MNT_UPDATE stuff for null mounts.  MNT_UPDATE implementations only
    allow certain flags to be changed out from under the mounted filesystem.
    For null mounts basically the only thing you can update is read-only
    vs read-write operation.

You can see how other VFSs handle MNT_UPDATE.  It is fairly
    straightforward.

-Matt
                    Matthew Dillon 
                    <dillon@backplane.com>

Salute.

I have a patch here:
http://leaf.dragonflybsd.org/~beket/updnull.diff

I have tested it extensively and it works. Stuff I tried:

1. Switching between ro/rw in a local null mount.
And verified read-onlyness by trying to touch a file.

2. Switching between ro/rw in stacks of local null mounts.
And verified read-onlyness by trying to touch a file.

3. Switching between ro/rw in a NFS exported null mount.
Specifically, /pfs/@@-1:00004 was null mounted on /home. And /home was NFS
shared with dfly being the server. NFS client was opensolaris build 126. I was
able to write from osol when /home was exported as read-write, and failed to do
so when it was exported as read-only. Client correctly reported that fs was
read-only. And so did mount(8) in the server side.

I can provide copy/pastes from sessions, upon request. But better, fetch the
patch and try it yourself :)

This http://leaf.dragonflybsd.org/~beket/mountnull.png shows some preliminary
tests I did (they do not cover switching back to ro from rw, or 3.)

Best regards,
Stathis Kamperis

Backed it off for now, Ì am doing a small change & publishing it again later :)

Should be ok now. Sorry for the spam :)

Stathis

Ping!

Anyone interested with time and clue to review the patch ?
I'd like to push it at some point, before it gets too stale, but ain't gonna
happen if at least someone else gives me a thumbs up.

Cheers,
Stathis

:Stathis Kamperis <ekamperi@gmail.com> added the comment:
:
:Ping!
:
:Anyone interested with time and clue to review the patch ?
:I'd like to push it at some point, before it gets too stale, but ain't gonn=
:a
:happen if at least someone else gives me a thumbs up.
:
:Cheers,
:Stathis

It looks committable to me.   The only possible issue is whether
    the type field for mount -u operations can ever be NULL.  It
    doesn't seem to ever be NULL so I think we're ok there.

-Matt
                    Matthew Dillon 
                    <dillon@backplane.com>

On Thu, Nov 19, 2009 at 08:40:46AM +0000, Stathis Kamperis (via DragonFly issue tracker) wrote:

Stathis Kamperis <ekamperi@gmail.com> added the comment:

Ping!

Anyone interested with time and clue to review the patch ?
I'd like to push it at some point, before it gets too stale, but ain't gonna
happen if at least someone else gives me a thumbs up.

I noticed that I can't remount nullfs by mount(8). The patched
mount_null accepts only one argument (the mountpoint to be remounted)
when MNT_UPDATE is specified either by -u or by -o update, but
what mount(8) passes to filesystem-specific mount commands like this: # mount -ur /mnt/pt
-> mount_${foo} -o ro -o update /path/to/special /mnt/pt # mount -uw /mnt/pt
-> mount_${foo} -o noro -o update /path/to/special /mnt/pt

I think that the following patch on top of yours does this for you,
although I only tested it slightly.

diff --git a/sbin/mount_null/mount_null.c b/sbin/mount_null/mount_null.c
index b9c595a..9e02b6d 100644
--- a/sbin/mount_null/mount_null.c
+++ b/sbin/mount_null/mount_null.c
@ -88,29 +88,20 @ main(int argc, char **argv)
argv += optind;

/*
-     * Only the mount point need be specified in update mode.
+     * Resolve target and source with realpath(3).  Only the mount point
+     * needs be specified in update mode, but mount(8) passes us two
+     * arguments, the second of which is the source directory.
      /
-    if (mntflags & MNT_UPDATE) {
-        if (argc != 1) {
-            usage();
-            / not reached */
-        }
+    if ((mntflags & MNT_UPDATE) && argc == 1) {
+        args.target = NULL;
         checkpath(argv[0], source);
-        error = getvfsbyname("null", &vfc);
-        if (error)
-            err(1, "getvfsbyname");
-        if (mount(vfc.vfc_name, source, mntflags, &args))
-            err(1, "mount");
-        exit(0);
-    }

    if (argc < 2)
+    } else if (argc == 2) {
+        args.target = target;
+        checkpath(argv[0], target);
+        checkpath(argv[1], source);
+    } else
         usage();

- /* resolve target and source with realpath(3) /
- checkpath(argv⁰, target);
- checkpath(argv¹, source);
-
/ * Mount points that did not use distinct paths (e.g. / on /mnt) * used to be disallowed because mount linkages were stored in
@ -118,7 +109,6 @ main(int argc, char **argv) * stores mount linkages in the namecache topology and does not * have this problem, so paths no longer need to be distinct.
*/
- args.target = target;

error = getvfsbyname("null", &vfc);
     if (error && vfsisloadable("null")) {

I noticed that I can't remount nullfs by mount(8). The patched
mount_null accepts only one argument (the mountpoint to be remounted)
when MNT_UPDATE is specified either by -u or by -o update, but
what mount(8) passes to filesystem-specific mount commands like this:

1. mount ur /mnt/pt
   > mount_${foo} -o ro -o update /path/to/special /mnt/pt
2. mount uw /mnt/pt
   > mount_${foo} -o noro -o update /path/to/special /mnt/pt

I think that the following patch on top of yours does this for you,
although I only tested it slightly.

I'm in the middle of a build. Once it finishes, I'll apply your modifications on
top of my patch & re-run all the tests I've done so far, plus your test cases
that involve mount(8).

If everything works and given that Dillon didn't object, I'll push it in the
next couple of days.

Thanks!

Cheers,
Stathis

Fixed with 8b02b69a65f3a7c5d344957f9ee3162b20077c93