Making Linux stat() less evil

[Alexander Leidinger]

Quoting Ed Schouten <ed at 80386.nl> (from Thu, 19 Feb 2009 22:27:49 +0100):

> Roman,
>
> After some discussion with kib@ on IRC, I changed the patch a little: I
> added a new function called kern_statat_vnhook(). This function allows
> the Linuxolator to use a hook to modify struct stat, to reduce some
> redundant code:
>
> 	http://80386.nl/pub/linux-stat.diff
>
> Shall I commit this patch to SVN?

 From your patch:
---snip---
@@ -2359,6 +2366,8 @@
  	vfslocked = NDHASGIANT(&nd);
  	error = vn_stat(nd.ni_vp, &sb, td->td_ucred, NOCRED, td);
  	if (!error) {
+		if (hook != NULL)
+			hook(nd.ni_vp, &sb);
  		SDT_PROBE(vfs, , stat, mode, path, sb.st_mode, 0, 0, 0);
  		if (S_ISREG(sb.st_mode))
  			SDT_PROBE(vfs, , stat, reg, path, pathseg, 0, 0, 0);
---snip---

I think you should call the hook after SDT_PROBE, not before. This way  
it doesn't matter what the hook does to sb, the dtrace probe will get  
what it expects (the FreeBSD style sb). I don't think we need to add  
another dtrace probe here after the probe, as I think this should be  
handled somewhere near the code of the hook (in this case in the  
linuxulator... which means I will take care about this in my  
linuxulator-dtrace branch).

Bye,
Alexander.

-- 
You are a bundle of energy, always on the go.

http://www.Leidinger.net    Alexander @ Leidinger.net: PGP ID = B0063FE7
http://www.FreeBSD.org       netchild @ FreeBSD.org  : PGP ID = 72077137