linux-ext4 - Re: [PATCHv3 6/6] Documentation: Correct the description of FIEMAP_EXTENT

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Date:   Wed, 26 Feb 2020 05:05:03 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Ritesh Harjani <riteshh@...ux.ibm.com>
Cc:     jack@...e.cz, tytso@....edu, linux-ext4@...r.kernel.org,
        adilger.kernel@...ger.ca, linux-fsdevel@...r.kernel.org,
        darrick.wong@...cle.com, hch@...radead.org, cmaiolino@...hat.com
Subject: Re: [PATCHv3 6/6] Documentation: Correct the description of
 FIEMAP_EXTENT_LAST

On Wed, Feb 26, 2020 at 03:27:08PM +0530, Ritesh Harjani wrote:
> Currently FIEMAP_EXTENT_LAST is not working consistently across
> different filesystem's fiemap implementations and thus this feature
> may be broken. So fix the documentation about this flag to meet the
> right expectations.

Are you saying filesystems have both false positives and false negatives?
I can understand how a filesystem might fail to set FIEMAP_EXTENT_LAST,
but not how a filesystem might set it when there's actually another
extent beyond this one.

>  * FIEMAP_EXTENT_LAST
> -This is the last extent in the file. A mapping attempt past this
> -extent will return nothing.
> +This is generally the last extent in the file. A mapping attempt past this
> +extent may return nothing. But the user must still confirm by trying to map
> +past this extent, since different filesystems implement this differently.