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From: Stefan Metzmacher <metze@samba.org>
To: Jens Axboe <axboe@kernel.dk>, io-uring@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk
Subject: Re: [PATCH 3/6] io_uring: add support for IORING_OP_OPENAT
Date: Wed, 8 Jan 2020 18:04:01 +0100
Message-ID: <d0f0e726-8e6f-aa43-07b6-fdb3b49ce1bc@samba.org> (raw)
In-Reply-To: <9672da37-bf6f-ce2d-403c-5e2692c67782@kernel.dk>

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Am 08.01.20 um 17:40 schrieb Jens Axboe:
> On 1/8/20 9:32 AM, Stefan Metzmacher wrote:
>> Am 08.01.20 um 17:20 schrieb Jens Axboe:
>>> On 1/8/20 6:05 AM, Stefan Metzmacher wrote:
>>>> Hi Jens,
>>>>
>>>>> This works just like openat(2), except it can be performed async. For
>>>>> the normal case of a non-blocking path lookup this will complete
>>>>> inline. If we have to do IO to perform the open, it'll be done from
>>>>> async context.
>>>>
>>>> Did you already thought about the credentials being used for the async
>>>> open? The application could call setuid() and similar calls to change
>>>> the credentials of the userspace process/threads. In order for
>>>> applications like samba to use this async openat, it would be required
>>>> to specify the credentials for each open, as we have to multiplex
>>>> requests from multiple user sessions in one process.
>>>>
>>>> This applies to non-fd based syscall. Also for an async connect
>>>> to a unix domain socket.
>>>>
>>>> Do you have comments on this?
>>>
>>> The open works like any of the other commands, it inherits the
>>> credentials that the ring was setup with. Same with the memory context,
>>> file table, etc. There's currently no way to have multiple personalities
>>> within a single ring.
>>
>> Ah, it's user = get_uid(current_user()); and ctx->user = user in
>> io_uring_create(), right?
> 
> That's just for the accounting, it's the:
> 
> ctx->creds = get_current_cred();

Ok, I just looked at an old checkout.

In kernel-dk-block/for-5.6/io_uring-vfs I see this only used in
the async processing. Does a non-blocking openat also use ctx->creds?

>>> Sounds like you'd like an option for having multiple personalities
>>> within a single ring?
>>
>> I'm not sure anymore, I wasn't aware of the above.
>>
>>> I think it would be better to have a ring per personality instead.
>>
>> We could do that. I guess we could use per user rings for path based
>> operations and a single ring for fd based operations.
>>
>>> One thing we could do to make this more lightweight
>>> is to have rings that are associated, so that we can share a lot of the
>>> backend processing between them.
>>
>> My current idea is to use the ring fd and pass it to our main epoll loop.
>>
>> Can you be more specific about how an api for associated rings could
>> look like?
> 
> The API would be the exact same, there would just be some way to
> associate rings when you create them. Probably a new field in struct
> io_uring_params (and an associated flag), which would tell io_uring that
> two separate rings are really the same "user". This would allow io_uring
> to use the same io-wq workqueues, for example, etc.

Ok, this would be just for better performance / better usage of
resources, right?

> This depends on the fact that you can setup the rings with the right
> personalities, that they would be known upfront. From your description,
> I'm not so sure that's the case? If not, then we would indeed need
> something that can pass in the credentials on a per-command basis. Not
> sure what that would look like.

We know the credentials and using a ring per user should be ok.

metze


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  reply index

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-07 17:00 [PATCHSET v2 0/6] io_uring: add support for open/close Jens Axboe
2020-01-07 17:00 ` [PATCH 1/6] fs: add namei support for doing a non-blocking path lookup Jens Axboe
2020-01-25 13:15   ` Jeff Layton
2020-01-07 17:00 ` [PATCH 2/6] fs: make build_open_flags() available internally Jens Axboe
2020-01-07 17:00 ` [PATCH 3/6] io_uring: add support for IORING_OP_OPENAT Jens Axboe
2020-01-08 13:05   ` Stefan Metzmacher
2020-01-08 16:20     ` Jens Axboe
2020-01-08 16:32       ` Stefan Metzmacher
2020-01-08 16:40         ` Jens Axboe
2020-01-08 17:04           ` Stefan Metzmacher [this message]
2020-01-08 22:53             ` Jens Axboe
2020-01-08 23:03               ` Stefan Metzmacher
2020-01-08 23:05                 ` Jens Axboe
2020-01-08 23:11                   ` Stefan Metzmacher
2020-01-08 23:22                     ` Jens Axboe
2020-01-09 10:40                       ` Stefan Metzmacher
2020-01-09 21:31                         ` Jens Axboe
2020-01-16 22:42                           ` Stefan Metzmacher
2020-01-17  0:16                             ` Jens Axboe
2020-01-07 17:00 ` [PATCH 4/6] fs: move filp_close() outside of __close_fd_get_file() Jens Axboe
2020-01-07 17:00 ` [PATCH 5/6] io-wq: add support for uncancellable work Jens Axboe
2020-01-07 17:00 ` [PATCH 6/6] io_uring: add support for IORING_OP_CLOSE Jens Axboe
2020-01-08 21:17 ` [PATCHSET v2 0/6] io_uring: add support for open/close Stefan Metzmacher
2020-01-08 22:57   ` Jens Axboe
2020-01-08 23:05     ` Stefan Metzmacher
2020-01-09  1:02       ` Jens Axboe
2020-01-09  2:03         ` Jens Axboe
2020-01-16 22:50           ` Stefan Metzmacher
2020-01-17  0:18             ` Jens Axboe
2020-01-20 12:15               ` Stefan Metzmacher
2020-01-20 13:04                 ` Pavel Begunkov
2020-01-17  0:44             ` Colin Walters
2020-01-17  0:51               ` Jens Axboe
2020-01-17  9:32               ` Pavel Begunkov
2020-01-17 15:21                 ` Jens Axboe
2020-01-17 22:27                   ` Pavel Begunkov
2020-01-17 22:36                     ` Jens Axboe

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