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Sun, 06 Oct 2024 04:46:47 -0400 X-MC-Unique: zGLFebcFPmm6-XbHhO86Xg-1 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 73C5E19772C6; Sun, 6 Oct 2024 08:46:46 +0000 (UTC) Received: from fedora (unknown [10.72.116.29]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 223EE3000198; Sun, 6 Oct 2024 08:46:41 +0000 (UTC) Date: Sun, 6 Oct 2024 16:46:36 +0800 From: Ming Lei To: Pavel Begunkov Cc: Jens Axboe , io-uring@vger.kernel.org, linux-block@vger.kernel.org, ming.lei@redhat.com Subject: Re: [PATCH V6 7/8] io_uring/uring_cmd: support provide group kernel buffer Message-ID: References: <20240912104933.1875409-1-ming.lei@redhat.com> <20240912104933.1875409-8-ming.lei@redhat.com> Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 On Fri, Oct 04, 2024 at 04:44:54PM +0100, Pavel Begunkov wrote: > On 9/12/24 11:49, Ming Lei wrote: > > Allow uring command to be group leader for providing kernel buffer, > > and this way can support generic device zero copy over device buffer. > > > > The following patch will use the way to support zero copy for ublk. > > > > Signed-off-by: Ming Lei > > --- > > include/linux/io_uring/cmd.h | 7 +++++++ > > include/uapi/linux/io_uring.h | 7 ++++++- > > io_uring/uring_cmd.c | 28 ++++++++++++++++++++++++++++ > > 3 files changed, 41 insertions(+), 1 deletion(-) > > > > diff --git a/include/linux/io_uring/cmd.h b/include/linux/io_uring/cmd.h > > index 447fbfd32215..fde3a2ec7d9a 100644 > > --- a/include/linux/io_uring/cmd.h > > +++ b/include/linux/io_uring/cmd.h > > @@ -48,6 +48,8 @@ void __io_uring_cmd_do_in_task(struct io_uring_cmd *ioucmd, > > void io_uring_cmd_mark_cancelable(struct io_uring_cmd *cmd, > > unsigned int issue_flags); > > +int io_uring_cmd_provide_kbuf(struct io_uring_cmd *ioucmd, > > + const struct io_uring_kernel_buf *grp_kbuf); > > #else > > static inline int io_uring_cmd_import_fixed(u64 ubuf, unsigned long len, int rw, > > struct iov_iter *iter, void *ioucmd) > > @@ -67,6 +69,11 @@ static inline void io_uring_cmd_mark_cancelable(struct io_uring_cmd *cmd, > > unsigned int issue_flags) > > { > > } > > +static inline int io_uring_cmd_provide_kbuf(struct io_uring_cmd *ioucmd, > > + const struct io_uring_kernel_buf *grp_kbuf) > > +{ > > + return -EOPNOTSUPP; > > +} > > #endif > > /* > > diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h > > index 2af32745ebd3..11985eeac10e 100644 > > --- a/include/uapi/linux/io_uring.h > > +++ b/include/uapi/linux/io_uring.h > > @@ -271,9 +271,14 @@ enum io_uring_op { > > * sqe->uring_cmd_flags top 8bits aren't available for userspace > > * IORING_URING_CMD_FIXED use registered buffer; pass this flag > > * along with setting sqe->buf_index. > > + * IORING_PROVIDE_GROUP_KBUF this command provides group kernel buffer > > + * for member requests which can retrieve > > + * any sub-buffer with offset(sqe->addr) and > > + * len(sqe->len) > > Is there a good reason it needs to be a cmd generic flag instead of > ublk specific? io_uring request isn't visible for drivers, so driver can't know if the uring command is one group leader. Another way is to add new API of io_uring_cmd_may_provide_buffer(ioucmd) so driver can check if device buffer can be provided with this uring_cmd, but I prefer to the new uring_cmd flag: - IORING_PROVIDE_GROUP_KBUF can provide device buffer in generic way. - ->prep() can fail fast in case that it isn't one group request > > 1. Extra overhead for files / cmds that don't even care about the > feature. It is just checking ioucmd->flags in ->prep(), and basically zero cost. > > 2. As it stands with this patch, the flag is ignored by all other > cmd implementations, which might be quite confusing as an api, > especially so since if we don't set that REQ_F_GROUP_KBUF memeber > requests will silently try to import a buffer the "normal way", The usage is same with buffer select or fixed buffer, and consumer has to check the flag. And same with IORING_URING_CMD_FIXED which is ignored by other implementations except for nvme, :-) I can understand the concern, but it exits since uring cmd is born. > i.e. interpret sqe->addr or such as the target buffer. > 3. We can't even put some nice semantics on top since it's > still cmd specific and not generic to all other io_uring > requests. > > I'd even think that it'd make sense to implement it as a > new cmd opcode, but that's the business of the file implementing > it, i.e. ublk. > > > */ > > #define IORING_URING_CMD_FIXED (1U << 0) > > -#define IORING_URING_CMD_MASK IORING_URING_CMD_FIXED > > +#define IORING_PROVIDE_GROUP_KBUF (1U << 1) > > +#define IORING_URING_CMD_MASK (IORING_URING_CMD_FIXED | IORING_PROVIDE_GROUP_KBUF) It needs one new file operation, and we shouldn't work toward this way. Thanks, Ming