Messages in this thread | | | Date | Fri, 23 Jul 2010 00:57:38 +1000 | From | Nick Piggin <> | Subject | Re: [RFC][PATCH] Add a dentry op to handle automounting rather than abusing follow_link |
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On Thu, Jul 22, 2010 at 01:36:27PM +0100, David Howells wrote: > Nick Piggin <npiggin@suse.de> wrote: > > > > AFS is made to use this facility so that it can be tested. Other > > > filesystems abusing the follow_mount() inode operation will also need to > > > be modified. > > I meant follow_link() here of course... Too many followy things:-) > > > How about having a .follow_mount op, and using that instead of > > default follow_mount in case mounted is incremented? > > But what if d_mounted is not incremented, though?
Nothing?
> That's usually the point > you'd want to call the automount code.
I think you have it the wrong way around. If you wanted to call the automount code, you would have incremented d_mounted.
> Why would you want to call into the > filesystem just to skip over possibly mounted dentries? A dentry may have an > elevated d_mount on it, but nothing mounted at that {vfsmount,dentry} point I > suppose, but still jumping into the filesystem just so it can skip an already > mounted point would seem a waste of time.
Those that don't care wouldn't set ->follow_mount though. Following a mount is a fairly heavy operation already, it does take a global lock (before vfs scalability patches, anyway).
I like the flexibility of doing one's own ->follow_mount, although Al might object to allowing filesystems to follow mounts in ways that are not published to the core namespace structures.
> > Also I would prefer the patch to add this call > > Meaning i_op->follow_mount()?
Either one, just make the follow_mount/__follow_mount API changes in one patch, and add the callback in another.
> > keep basically the same API as follow_mount, so if you are going to change > > that to return an error and do the NOFOLLOW handling in there, then could > > you do that first, as a more trivial patch? > > Ummm... I'm not sure I follow you. I changed __follow_mount() not > follow_mount(). I don't think changing the latter is necessary.
I meant __follow_mount.
> > Then your addition of the d_op should not touch outside *follow_mount. > > But calling i_op->follow_mount() would, so what does this gain you? And why > not touch the inside of __follow_mount()? > > Are you suggesting doing i_op->follow_mount() instead of or as well as > d_op->d_automount()? I'm not entirely sure.
Two suggestions. Firstly a d_op->d_follow_mount() (does following a mount even make sense at the inode level?)
Secondly, just simply to split the patch so you change the __follow_mount API in namespace first.
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