Re: [PATCH 1/3] [RFC] genhd: add a new attribute in device structure

From: Kay Sievers
Date: Thu Jun 16 2011 - 14:42:40 EST

On Thu, Jun 16, 2011 at 20:15, Douglas Gilbert <dgilbert@xxxxxxxxxxxx> wrote:
> On 11-06-16 02:05 PM, Kay Sievers wrote:
>>> The kernel's device naming (following from how devices are
>>> discovered) is topological. However at higher levels
>>> the user is interested in the device identity. So if
>>> unique device names were used as preferred names and
>>> preferred names were unique (in a Linux system at any
>>> given time) then any subsequent path to an existing device
>>> would be highlighted. [That is because subsequent attempts
>>> to create its preferred name would fail because it is
>>> already there.]
>>> You don't need thousands of dollars of equipment to
>>> demonstrate this point. An external single disk
>>> SATA enclosure with a USB and eSATA interface will do.
>> Udev does that already since quite a while. This is my cheap laptop:
>> Â # find /dev/disk/ -name "wwn*"
>> Â /dev/disk/by-id/wwn-0x50015179593f3038-part1
>> Â /dev/disk/by-id/wwn-0x50015179593f3038-part4
>> Â /dev/disk/by-id/wwn-0x50015179593f3038-part3
>> Â /dev/disk/by-id/wwn-0x50015179593f3038-part2
>> Â /dev/disk/by-id/wwn-0x50015179593f3038
> That is my point, if that disk is eSATA and USB connected
> which transport is that link pointing to? I would
> prefer eSATA over USB any day but is udev that smart? Or
> are we just seeing a symlink to the first (or perhaps last)
> path discovered?

I don't know if any bridge supports both connections at the same time.
Mine doesn't.

If two kernel devices fight for the same link, the last one wins,
unless there are link-priorities specified in udev rules.

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