From: Richard Weinberger <richard@nod.at>
To: "J. Bruce Fields" <bfields@fieldses.org>
Cc: linux-mtd@lists.infradead.org, david@sigma-star.at,
tytso@mit.edu, dedekind1@gmail.com, adrian.hunter@intel.com,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
adilger.kernel@dilger.ca, akpm@linux-foundation.org,
linux-ext4@vger.kernel.org
Subject: Re: [PATCH 3/6] ubifs: Use 64bit readdir cookies
Date: Thu, 29 Dec 2016 17:36:35 +0100 [thread overview]
Message-ID: <224abf2f-c820-5df1-6292-42c1e2d47933@nod.at> (raw)
In-Reply-To: <20161229161534.GA29261@fieldses.org>
Bruce,
On 29.12.2016 17:15, J. Bruce Fields wrote:
> On Thu, Dec 29, 2016 at 04:49:54PM +0100, Richard Weinberger wrote:
>> 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.
>
> Unlink takes (parent directory, name), not a directory cookie.
>
> The problem is concurrent unlink and nfs readdir. So:
>
> NFS server returns readdir result with cookie X
>
> Somebody unlinks the entry at X.
>
> NFS server gets readdir request with cookie X.
>
> Then the NFS client will get a spurious -ENOENT.
Ah yes. Sorry I misunderstood your question.
UBIFS readdir() address this already, if you ask it to readdir()
from pos X and X is not present it will jump to the next best entry X'.
UBIFS does so since ever.
Thanks,
//richard
next prev parent reply other threads:[~2016-12-29 16:36 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-01 22:02 [PATCH 0/6] UBIFS NFS export support Richard Weinberger
2016-12-01 22:02 ` [PATCH 1/6] ext4: Move is_32bit_api() to generic code Richard Weinberger
2016-12-12 22:18 ` Richard Weinberger
2016-12-12 22:29 ` Andreas Dilger
2016-12-01 22:02 ` [PATCH 2/6] ubifs: Provide a custom llseek for directories Richard Weinberger
2016-12-01 22:02 ` [PATCH 3/6] ubifs: Use 64bit readdir cookies Richard Weinberger
2016-12-29 2:58 ` J. Bruce Fields
2016-12-29 9:19 ` Richard Weinberger
2016-12-29 15:34 ` J. Bruce Fields
2016-12-29 15:49 ` Richard Weinberger
2016-12-29 16:15 ` J. Bruce Fields
2016-12-29 16:36 ` Richard Weinberger [this message]
2016-12-29 16:59 ` J. Bruce Fields
2016-12-29 17:05 ` Richard Weinberger
2017-01-03 19:52 ` J. Bruce Fields
2016-12-01 22:02 ` [PATCH 4/6] ubifs: Maintain a parent pointer Richard Weinberger
2016-12-02 9:28 ` Marcus Folkesson
2016-12-02 10:36 ` Richard Weinberger
2017-04-28 8:31 ` Hyunchul Lee
2017-04-28 9:09 ` Richard Weinberger
2016-12-01 22:02 ` [PATCH 5/6] ubifs: Implement export_operations Richard Weinberger
2016-12-01 22:02 ` [PATCH 6/6] ubifs: Wire up NFS support Richard Weinberger
2016-12-29 2:56 ` J. Bruce Fields
2016-12-29 8:48 ` Richard Weinberger
2017-05-21 20:20 [PATCH 0/6] UBIFS NFS export support v2 Richard Weinberger
2017-05-21 20:20 ` [PATCH 3/6] ubifs: Use 64bit readdir cookies Richard Weinberger
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