[PATCH] autofs4 - use lookup access intent to support recursive bind mounts

[PATCH] autofs4 - use lookup access intent to support recursive bind mounts

[Ian Kent]

Hi Andrew,

For autofs maps that recursively reference other map entries in their
mount point path we need to ensure that these mounts are performed
prior to the current mount request being done. We've used the access
system call, made just prior to performing the mount, to make this
happen. In the case of bind mounts, however, the lookup flags in 
the path walk don't trigger a mount. To do this we need to also
trigger a mount when we see the LOOKUP_ACCESS flag.

Signed-off-by: Ian Kent <raven@themaw.net>

Ian

---
diff -up linux-2.6.25-mm1/fs/autofs4/root.c.lookup-access-intent-trigger linux-2.6.25-mm1/fs/autofs4/root.c
--- linux-2.6.25-mm1/fs/autofs4/root.c.lookup-access-intent-trigger	2008-04-28 11:33:20.000000000 +0800
+++ linux-2.6.25-mm1/fs/autofs4/root.c	2008-04-28 11:36:06.000000000 +0800
@@ -19,6 +19,8 @@
 #include <linux/time.h>
 #include "autofs_i.h"
 
+#define LOOKUP_TRIGGER_FLAGS (LOOKUP_CONTINUE|LOOKUP_DIRECTORY|LOOKUP_ACCESS)
+
 static int autofs4_dir_symlink(struct inode *,struct dentry *,const char *);
 static int autofs4_dir_unlink(struct inode *,struct dentry *);
 static int autofs4_dir_rmdir(struct inode *,struct dentry *);
@@ -291,7 +293,7 @@ static int try_to_fill_dentry(struct den
 			return status;
 		}
 	/* Trigger mount for path component or follow link */
-	} else if (flags & (LOOKUP_CONTINUE | LOOKUP_DIRECTORY) ||
+	} else if (flags & LOOKUP_TRIGGER_FLAGS ||
 			current->link_count) {
 		DPRINTK("waiting for mount name=%.*s",
 			dentry->d_name.len, dentry->d_name.name);
@@ -335,7 +337,7 @@ static void *autofs4_follow_link(struct 
 		nd->flags);
 
 	/* If it's our master or we shouldn't trigger a mount we're done */
-	lookup_type = nd->flags & (LOOKUP_CONTINUE | LOOKUP_DIRECTORY);
+	lookup_type = nd->flags & LOOKUP_TRIGGER_FLAGS;
 	if (oz_mode || !lookup_type)
 		goto done;
 

Re: [PATCH] autofs4 - use lookup access intent to support recursive bind mounts

[Al Viro]

On Mon, Apr 28, 2008 at 02:14:54PM +0800, Ian Kent wrote:
> 
> Hi Andrew,
> 
> For autofs maps that recursively reference other map entries in their
> mount point path we need to ensure that these mounts are performed
> prior to the current mount request being done. We've used the access
> system call, made just prior to performing the mount, to make this
> happen. In the case of bind mounts, however, the lookup flags in 
> the path walk don't trigger a mount. To do this we need to also
> trigger a mount when we see the LOOKUP_ACCESS flag.

That's too fscking bad, since ->lookup() is about to lose access to
nameidata *and* flags for anything but the last step.  IOW, we'll need
cleaner solution...

Re: [PATCH] autofs4 - use lookup access intent to support recursive bind mounts

[Ian Kent]

On Mon, 2008-04-28 at 07:22 +0100, Al Viro wrote:
> On Mon, Apr 28, 2008 at 02:14:54PM +0800, Ian Kent wrote:
> > 
> > Hi Andrew,
> > 
> > For autofs maps that recursively reference other map entries in their
> > mount point path we need to ensure that these mounts are performed
> > prior to the current mount request being done. We've used the access
> > system call, made just prior to performing the mount, to make this
> > happen. In the case of bind mounts, however, the lookup flags in 
> > the path walk don't trigger a mount. To do this we need to also
> > trigger a mount when we see the LOOKUP_ACCESS flag.
> 
> That's too fscking bad, since ->lookup() is about to lose access to
> nameidata *and* flags for anything but the last step.  IOW, we'll need
> cleaner solution...

Spell it out for me please!
Ian

Re: [PATCH] autofs4 - use lookup access intent to support recursive bind mounts

[Al Viro]

On Mon, Apr 28, 2008 at 02:38:25PM +0800, Ian Kent wrote:
> 
> On Mon, 2008-04-28 at 07:22 +0100, Al Viro wrote:
> > On Mon, Apr 28, 2008 at 02:14:54PM +0800, Ian Kent wrote:
> > > 
> > > Hi Andrew,
> > > 
> > > For autofs maps that recursively reference other map entries in their
> > > mount point path we need to ensure that these mounts are performed
> > > prior to the current mount request being done. We've used the access
> > > system call, made just prior to performing the mount, to make this
> > > happen. In the case of bind mounts, however, the lookup flags in 
> > > the path walk don't trigger a mount. To do this we need to also
> > > trigger a mount when we see the LOOKUP_ACCESS flag.
> > 
> > That's too fscking bad, since ->lookup() is about to lose access to
> > nameidata *and* flags for anything but the last step.  IOW, we'll need
> > cleaner solution...
> 
> Spell it out for me please!

->lookup() and friends are going to stop getting struct nameidata *.
->follow_link() obviously will keep it; ->d_revalidate() should
lose the sucker, but we might have to split it in two methods (which
is probably what'll be needed in your case).

At the same time struct open_intent is going to die, BTW, but that
won't matter for autofs, AFAICT.

Re: [PATCH] autofs4 - use lookup access intent to support recursive bind mounts

[Ian Kent]

On Mon, 2008-04-28 at 08:05 +0100, Al Viro wrote:
> On Mon, Apr 28, 2008 at 02:38:25PM +0800, Ian Kent wrote:
> > 
> > On Mon, 2008-04-28 at 07:22 +0100, Al Viro wrote:
> > > On Mon, Apr 28, 2008 at 02:14:54PM +0800, Ian Kent wrote:
> > > > 
> > > > Hi Andrew,
> > > > 
> > > > For autofs maps that recursively reference other map entries in their
> > > > mount point path we need to ensure that these mounts are performed
> > > > prior to the current mount request being done. We've used the access
> > > > system call, made just prior to performing the mount, to make this
> > > > happen. In the case of bind mounts, however, the lookup flags in 
> > > > the path walk don't trigger a mount. To do this we need to also
> > > > trigger a mount when we see the LOOKUP_ACCESS flag.
> > > 
> > > That's too fscking bad, since ->lookup() is about to lose access to
> > > nameidata *and* flags for anything but the last step.  IOW, we'll need
> > > cleaner solution...
> > 
> > Spell it out for me please!
> 
> ->lookup() and friends are going to stop getting struct nameidata *.
> ->follow_link() obviously will keep it; ->d_revalidate() should
> lose the sucker, but we might have to split it in two methods (which
> is probably what'll be needed in your case).

Right.

I don't see that yet in 2.6.25-mm1, are there any preliminary patches I
could look at?

> 
> At the same time struct open_intent is going to die, BTW, but that
> won't matter for autofs, AFAICT.

Yep, autofs doesn't care about this, it only cares about being able to
ask userspace to try a mount when needed.

Actually, using the flags to decide when to call back the daemon
wouldn't be needed at all except for mount storms caused by aggressive
GUI file system scanning and color ls and the like. 

Ian

Re: [PATCH] autofs4 - use lookup access intent to support recursive bind mounts

[Ian Kent]

On Mon, 2008-04-28 at 15:25 +0800, Ian Kent wrote:
> > ->lookup() and friends are going to stop getting struct nameidata *.
> > ->follow_link() obviously will keep it; ->d_revalidate() should
> > lose the sucker, but we might have to split it in two methods (which
> > is probably what'll be needed in your case).
> 
> Right.

Would it be sensible to use dentry->d_flags for this purpose?
Ian