From: Christoph Hellwig <hch@lst.de>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>,
jaxboe@fusionio.com, peterz@infradead.org,
akpm@linux-foundation.org, kay.sievers@vrfy.org,
viro@zeniv.linux.org.uk, linux-mm@kvack.org,
linux-fsdevel@vger.kernel.org
Subject: Re: struct backing_dev - purpose and life time rules
Date: Tue, 27 Jul 2010 16:09:47 +0200 [thread overview]
Message-ID: <20100727140947.GA25106@lst.de> (raw)
In-Reply-To: <20100727133956.GA7347@redhat.com>
On Tue, Jul 27, 2010 at 09:39:56AM -0400, Vivek Goyal wrote:
> How can I do it better?
>
> I needed a unique identifier with which user can work in terms of
> specifying weights to devices and in terms of understanding what stats
> mean. Device major/minor number looked like a obivious choice.
>
> I was looking for how to determine what is the major/minor number of disk
> request queue is associated with and I could use bdi to do that.
The problem is that a queue can be shared between multiple gendisks,
so dev_t of a gendisk is not a unique identifier. In addition to that
we even have gendisks that do not even have a block device associated
with them (e.g. for scsi tapes) or request queues that do not have
any gendisks attached to it (e.g. scsi devices without an ULD like
various types of scanners or printers).
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next prev parent reply other threads:[~2010-07-27 14:09 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-07-27 9:01 struct backing_dev - purpose and life time rules Christoph Hellwig
2010-07-27 9:14 ` Christoph Hellwig
2010-07-27 13:39 ` Vivek Goyal
2010-07-27 14:09 ` Christoph Hellwig [this message]
2010-07-27 23:55 ` FUJITA Tomonori
2010-07-28 4:42 ` Kay Sievers
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