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From: Matthew Wilcox <willy@infradead.org>
To: Carlos Maiolino <cmaiolino@redhat.com>
Cc: linux-fsdevel@vger.kernel.org, hch@lst.de, adilger@dilger.ca,
	darrick.wong@oracle.com
Subject: Re: Extending FIEMAP ioctl to report device id
Date: Mon, 11 Feb 2019 07:23:46 -0800	[thread overview]
Message-ID: <20190211152345.GC12668@bombadil.infradead.org> (raw)
In-Reply-To: <20190211094306.fjr6gfehcstm7eqq@hades.usersys.redhat.com>

On Mon, Feb 11, 2019 at 10:43:06AM +0100, Carlos Maiolino wrote:
> - The general idea, is to provide a way for FIEMAP ioctls to return the device
>   id where each extent is physically located.

How does userspace get to use this information?  If I call fiemap() and
it tells me extent 1 is on device 0x12345678 and extent 2 is on device
0x34567812, what can I do with that information?

Bear in mind that glibc uses a different dev_t from the kernel.

> - This is particularly useful for those filesystems where the file extents are
>   located on a different block device other than that associated with the
>   superblock , for example, btrfs using multiple devices, and XFS when using a
>   real-time device.

Darrick said it was useful for _inside_ the kernel.  How is it useful
for outside the kernel?


  parent reply	other threads:[~2019-02-11 15:23 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-11  9:43 Extending FIEMAP ioctl to report device id Carlos Maiolino
2019-02-11 11:29 ` Nikolay Borisov
2019-02-11 14:56   ` Carlos Maiolino
2019-02-11 15:23 ` Matthew Wilcox [this message]
2019-02-11 20:52   ` Andreas Dilger
2019-02-11 21:34     ` Dave Chinner

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