Re: [PATCH v7] generic: initial fiemap range query test

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On 12/6/17 3:57 PM, Dave Chinner wrote:

> There's a *simple answer* to this problem: fix the new command's
> output.
> 
> That is: the user asked for a specific range, so the command itself
> should trim the map returned by the kernel to only display the exact
> range the user asked for.  Then it doesn't matter if the underlying
> filesystem trims the extents or not, because the we're going to do
> that anyway in userspace.

I have a different opinion:

xfs_io is a debugging tool; the fiemap command sends an ioctl to the kernel.

Ranged fiemap queries are a real thing; you put numbers into the kernel,
and you get numbers out of the kernel.

IMNSO, xfs_io should present to the user /what the kernel returned/,
and not re-interpret it to fit some other notion of correctness if we
don't like what the kernel told us.

If you want to have some user-friendlier behavior where xfs_io layers
behaviors on top of what the kernel provides, then add a "-t" argument for trim,
but hiding ioctl inconsistencies by filtering them through xfs_io sounds
like the wrong approach to me.

-Eric
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