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([2620:10d:c092:600::1:bf9]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6631448605fsm476072a12.12.2026.03.11.04.30.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 11 Mar 2026 04:30:35 -0700 (PDT) Message-ID: <086190ca-1c34-448f-a565-aa41f671971f@gmail.com> Date: Wed, 11 Mar 2026 11:30:33 +0000 Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] io_uring: Add IORING_OP_DUP To: Daniele Di Proietto , Jens Axboe Cc: io-uring@vger.kernel.org References: <20260310154933.2500971-1-daniele.di.proietto@gmail.com> Content-Language: en-US From: Pavel Begunkov In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 3/10/26 18:42, Daniele Di Proietto wrote: > On Tue, Mar 10, 2026 at 4:24 PM Jens Axboe wrote: >> >> On 3/10/26 9:49 AM, Daniele Di Proietto wrote: >>> The new operation is like dup3(). The source file can be a regular file >>> descriptor or a direct descriptor. The destination is a regular file >>> descriptor. >>> >>> The direct descriptor variant is useful to move a descriptor to an fd >>> and close the existing fd with a single acquisition of the `struct >>> files_struct` `file_lock`. Combined with IORING_OP_ACCEPT or >>> IORING_OP_OPENAT2 with direct descriptors, it can reduce lock contention >>> for multithreaded applications. >> >> Overall comment - how does this interact with direct descriptors? Feels >> like this should support both, rather than just normal file descriptors. > > As implemented, the operation supports: > 1. src: direct, dst: normal (this is the use case I mostly care about) > 2. src: normal, dst: normal () > > I can extend it to also support > 3. src: direct, dst: direct > 4, src: normal, dst: direct > > I can use IOSQE_FIXED_FILE to pick the source and I guess I can use a > bit in dup_flags (something like IORING_DUP_DIRECT) to decide whether > the destination is a direct descriptor or normal. > > Does that make sense? Let's not try to reuse IOSQE_FIXED_FILE for that. We may want to operate with io_uring's filetable entries and not just files you get from there. Two separate IORING_DUP_* flags should be better. And you can extract a helper function out of io_uring/splice.c::io_splice_get_file() It might also be better to make it a part of IORING_OP_FILES_UPDATE instead of wasting another opcode, and liburing can provide a prep_dup helper for convenience. -- Pavel Begunkov