Benjamin Kaduk wrote:
>
> If we're confident that we won't ever fully fill the hash table, I
> would
> think that this should wrap around back to zero (or one?) instead of
> overflowing.
>
Here's my updated patch (it will wrap to 1 the first time and then
exceed 255 if 1<->255 are all in use).
--- kern/vfs_init.c.sav 2011-06-11 18:58:33.000000000 -0400
+++ kern/vfs_init.c 2011-08-25 11:09:14.000000000 -0400
@@ -39,6 +39,7 @@ __FBSDID("$FreeBSD: head/sys/kern/vfs_in
#include <sys/param.h>
#include <sys/systm.h>
+#include <sys/fnv_hash.h>
#include <sys/kernel.h>
#include <sys/linker.h>
#include <sys/mount.h>
@@ -138,6 +139,9 @@ vfs_register(struct vfsconf *vfc)
struct sysctl_oid *oidp;
struct vfsops *vfsops;
static int once;
+ struct vfsconf *tvfc;
+ uint32_t hashval;
+ int secondpass;
if (!once) {
vattr_null(&va_null);
@@ -152,7 +156,31 @@ vfs_register(struct vfsconf *vfc)
if (vfs_byname(vfc->vfc_name) != NULL)
return EEXIST;
- vfc->vfc_typenum = maxvfsconf++;
+ /*
+ * Calculate a hash on vfc_name to use for vfc_typenum. Unless
+ * all of 1<->255 are assigned, it is limited to 8bits since that is
+ * what ZFS uses from vfc_typenum and is also the preferred range
+ * for vfs_getnewfsid().
+ */
+ hashval = fnv_32_str(vfc->vfc_name, FNV1_32_INIT);
+ hashval &= 0xff;
+ secondpass = 0;
+ do {
+ /* Look for and fix any collision. */
+ TAILQ_FOREACH(tvfc, &vfsconf, vfc_list) {
+ if (hashval == tvfc->vfc_typenum) {
+ if (hashval == 255 && secondpass == 0) {
+ hashval = 1;
+ secondpass = 1;
+ } else
+ hashval++;
+ break;
+ }
+ }
+ } while (tvfc != NULL);
+ vfc->vfc_typenum = hashval;
+ if (vfc->vfc_typenum >= maxvfsconf)
+ maxvfsconf = vfc->vfc_typenum + 1;
TAILQ_INSERT_TAIL(&vfsconf, vfc, vfc_list);
/*
> Do we need to care about something attempting to add the same vfc_name
> twice? This code will happily add a second entry at the next available
> index.
>
If file systems use VFS_SET(), I don't think this can happen, since the
same vfc_name would imply "same module name" and the 2nd one wouldn't load.
(Been there, w.r.t. nfs.)
> > + break;
> > + }
> > + }
> > + } while (tvfc != NULL);
> > + vfc->vfc_typenum = hashval;
> > + if (vfc->vfc_typenum >= maxvfsconf)
> > + maxvfsconf = vfc->vfc_typenum + 1;
>
> I guess we're holding off on killing maxvfsconf until after 9.0 is
> out?
Well, I still don't know if anything has a use for vfs_sysctl(), so
I'm not volunteering to take it out. (If others feel it should come
out for 9.0, maybe... But I would still consider that a separate patch.)
rick
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