Date: Mon, 26 Jun 2006 06:51:37 +0000 From: "Poul-Henning Kamp" <phk@phk.freebsd.dk> To: John-Mark Gurney <gurney_j@resnet.uoregon.edu> Cc: pjd@freebsd.org, freebsd-arch@freebsd.org Subject: Re: Accessing disks via their serial numbers. Message-ID: <33398.1151304697@critter.freebsd.dk> In-Reply-To: Your message of "Sun, 25 Jun 2006 20:16:37 MST." <20060626031636.GK82074@funkthat.com>
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In message <20060626031636.GK82074@funkthat.com>, John-Mark Gurney writes:
>Can't we expand the disk api? add a const char *d_serial to the struct
>disk, and have the disk api automaticly propegate the serial number up
>to the geom layer?
This is more or less what Pawel asked me for, and I am not at all
convinced that is how we want to do it.
There are several attributes which could be relevant in a context
like what Pawel proposes, the serial number (which one ? drive or
media ?) the physical address cam-{bus,id,lun}, FC WWN's and so on.
If we disregard mechanism for a moment, and assume that g_label gets
hold of the info and creates label devices matching these various
informations, then we have to address the problem of obsesity in
the geom mesh:
In addition to ad0, ad0s1 and ad0s1a we will then have label/SOMESERIAL,
label/SOMESERIALs1, label/SOMESERIALs1a etc etc.
The better way of implementing it is by using the devfs 'device-on-demand'
facility to create symlinks to the geom_dev nodes based on specific
lookups, that would not pollute /dev with nodes people don't really
use and it would avoid the combinatorial explosion of the geom mesh.
And this brings me to the next point: As nice as this feature
sounds to begin with, is it really useful in practice ?
I suspect that the proponents of this scheme will object to my proposal
because they can not do a "ls /dev/mumble/*" to get a list of disk
serial numbers, and if so, that dooms the proposal: If the only objective
is to get a list of serial numbers, then this is not how it should be
done, instead we should add a real VPD registry to the kernel.
Summary:
I'm against until somebody have explained what the use is, and if
use is proven, it should be done with devfs device-on-demand(/cloning)
instead of g_label.
Poul-Henning
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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