Unmounting by filesystem ID

Daniel C. Sobral dcs at tcoip.com.br
Thu Jul 3 11:11:35 PDT 2003

Ian Dowse wrote:
> The patch below adds a new mount flag MNT_BYFSID that can be used
> to unmount a filesystem by specifying its filesystem ID instead of
> a path. The umount utility is changed to use this mechanism by
> default. This approach has a number of advantages:
> - It avoids any lookup operations that could potentially block
>   forever, so filesystems such as NFS can be reliably unmounted
>   even if the server is not responding but looking up the root node
>   would require an RPC (maybe to an underlying filesystem).
> - The filesystem specification is unambiguous, so umount(8) can
>   be sure that it is unmounting the correct filesystem (more
>   work in umount(8) may be required here).
> - Detached filesystems can be unmounted. If a filesystem becomes
>   detached from the filesystem hierarchy because the underlying
>   filesystem got unmounted, it does not require a reboot to unmount
>   it.
> Since unmounting by a path name is now only required for compatibility,
> in that case unmount() now just does a string comparison to find
> the correct filesystem. Also, this patch only affects unmounting;
> a similar approach could be applied to MNT_UPDATE mount operations.
> I would like to commit this during the next few days. Any comments
> or suggestions?

Just in the unlikely case no one has said this to your face yet, man, 
you rule.

Daniel C. Sobral                   (8-DCS)
Gerencia de Operacoes
Divisao de Comunicacao de Dados
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E-mail: Daniel.Capo at tco.net.br
         Daniel.Sobral at tcoip.com.br
         dcs at tcoip.com.br

	dcs at newsguy.com
	dcs at freebsd.org
	capo at notorious.bsdconspiracy.net

One time the police stopped me for speeding.  They said, "Don't you know the
speed limit is fifty-five miles an hour?"  I said, "Yeah, I know, but I 
going to be out that long."
		-- Steven Wright

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