linux-ext4 - Re: [PATCH 3/6] ubifs: Use 64bit readdir cookies

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Message-ID: <fe46ea3c-ef8f-40ba-f4ab-8dfe8faafb0b@nod.at>
Date:   Thu, 29 Dec 2016 16:49:54 +0100
From:   Richard Weinberger <richard@....at>
To:     "J. Bruce Fields" <bfields@...ldses.org>
Cc:     linux-mtd@...ts.infradead.org, david@...ma-star.at, tytso@....edu,
        dedekind1@...il.com, adrian.hunter@...el.com,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        adilger.kernel@...ger.ca, akpm@...ux-foundation.org,
        linux-ext4@...r.kernel.org
Subject: Re: [PATCH 3/6] ubifs: Use 64bit readdir cookies

Bruce,

On 29.12.2016 16:34, J. Bruce Fields wrote:
>> That way UBIFS can provide a 64bit readdir() cookie which is required for NFS3.
> 
> Sounds good.  And if a matching entry isn't found (as in the case of a
> concurrent unlink), what happens?  The answer must be the same as for
> ext4, but I've forgotten the details....  I guess it must find the next
> highest cookie (thinking of the cookie as a 64-bit integer of some kind)
> that exists in the directory.  And that must be the same order that
> readdir normally returns entries in.

If a 64bit cookie is not found, the lookup function returns -ENOENT.
In UBIFS we cannot just select a higher or lower key (cookie in this case),
since it is the B-tree key and would point to a completely different
entry.

So, in case of a concurrent unlink() one would succeed and one fail with
-ENOENT. Unless I miss something that seems okay to me.

Thanks,
//richard
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