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From: Pavel Begunkov <asml.silence@gmail.com>
To: Stefan Metzmacher <metze@samba.org>, Jens Axboe <axboe@kernel.dk>,
	io-uring@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk
Subject: Re: [PATCHSET v2 0/6] io_uring: add support for open/close
Date: Mon, 20 Jan 2020 16:04:44 +0300
Message-ID: <2fae1d5a-4dad-6435-04e9-e544c6c17f27@gmail.com> (raw)
In-Reply-To: <da05b8e8-4ef4-7527-36d5-511a192460f0@samba.org>

On 1/20/2020 3:15 PM, Stefan Metzmacher wrote:
> Hi Jens,
> 
>>> Thanks!
>>>
>>> Another great feature would the possibility to make use of the
>>> generated fd in the following request.
>>>
>>> This is a feature that's also available in the SMB3 protocol
>>> called compound related requests.
>>>
>>> The client can compound a chain with open, getinfo, read, close
>>> getinfo, read and close get an file handle of -1 and implicitly
>>> get the fd generated/used in the previous request.
>>
>> Right, the "plan" there is to utilize BPF to make this programmable.
>> We really need something more expressive to be able to pass information
>> between SQEs that are linked, or even to decide which link to run
>> depending on the outcome of the parent.
>>
>> There's a lot of potential there!
> 
> I guess so, but I don't yet understand how BPF works in real life.
> 
> Is it possible to do that as normal user without special privileges?
> 
> My naive way would be using some flags and get res and pass fd by reference.
> 
Just have been discussing related stuff. See the link if curious
https://github.com/axboe/liburing/issues/58

To summarise, there won't be enough flags to cover all use-cases and it
will slow down the common path. There should be something with
zero-overhead if the feature is not used, and that's not the case with
flags. That's why it'd be great to have a custom eBPF program
(in-kernel) controlling what and how to do next.

I don't much about eBPF internals, but probably we will be able to
attach an eBPF program to io_uring instance. Though, not sure whether it
could be done without privileges.

-- 
Pavel Begunkov

  reply index

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-07 17:00 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
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 [this message]
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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