Date: Sun, 24 Jun 2001 11:42:04 -0400 (EDT) From: Zhihui Zhang <zzhang@cs.binghamton.edu> To: Terry Lambert <tlambert2@mindspring.com> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: Confusion with mknod() and devfs Message-ID: <Pine.SOL.4.21.0106241124300.22184-100000@opal> In-Reply-To: <3B350150.E6175A61@mindspring.com>
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On Sat, 23 Jun 2001, Terry Lambert wrote:
> Zhihui Zhang wrote:
> > I think you got me wrong. I was talking about a device
> > with more than one names. So we can have more than one
> > vnode for the same device. (If there is more than one name
> > to the same device in the same FS, they can share the vnode,
> > otherwise, they cannot.)
>
> This is not how it works. The specfs/devfs will return
> the same vnode.
>
> A "special device" file type in the traditional sense is
> a major/minor/{block|character} tuple.
>
> The entry in an FS that references this is _not_ where
> the vnode comes from, it's a hint to tell the system to
> get the vnode from a single place, instead (specfs in a
> traditional system, vfs in a less traditional system).
>
>
> > Specifically, I fail to understand why we reload the inode
> > in ufs_mknod():
>
> Because when you make the node, you may have an exiting
> open reference to the same major/minor/{block|character}
> tuple, and you don't want to duplicate it in the ihash
> cache.
>
Thanks. But I still don't get it. The ihash is keyed on i_dev (the
device where the filesystem is mounted on) and i_number.
If I have two names in a filesystem refer to the same device, then their
inode number must be different.
if two names from different filesystems refer to the same device, then
their i_dev is different even if their inode number may happen to be the
same.
So I do not see how can we avoid duplicate entries in the ihash cache.
-Zhihui
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