From patchwork Fri Oct 16 04:52:56 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Douglas Gilbert X-Patchwork-Id: 11840863 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 90D5514B2 for ; Fri, 16 Oct 2020 04:53:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7B72D20897 for ; Fri, 16 Oct 2020 04:53:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388294AbgJPExI (ORCPT ); Fri, 16 Oct 2020 00:53:08 -0400 Received: from smtp.infotech.no ([82.134.31.41]:44921 "EHLO smtp.infotech.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726710AbgJPExI (ORCPT ); Fri, 16 Oct 2020 00:53:08 -0400 Received: from localhost (localhost [127.0.0.1]) by smtp.infotech.no (Postfix) with ESMTP id 2219920425C; Fri, 16 Oct 2020 06:53:06 +0200 (CEST) X-Virus-Scanned: by amavisd-new-2.6.6 (20110518) (Debian) at infotech.no Received: from smtp.infotech.no ([127.0.0.1]) by localhost (smtp.infotech.no [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 8+pwfKrTq32T; Fri, 16 Oct 2020 06:53:04 +0200 (CEST) Received: from xtwo70.bingwo.ca (host-104-157-204-209.dyn.295.ca [104.157.204.209]) by smtp.infotech.no (Postfix) with ESMTPA id CF86120423B; Fri, 16 Oct 2020 06:53:02 +0200 (CEST) From: Douglas Gilbert To: linux-scsi@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Cc: martin.petersen@oracle.com, axboe@kernel.dk, bvanassche@acm.org Subject: [PATCH 2/4] scatterlist: add sgl_copy_sgl() function Date: Fri, 16 Oct 2020 00:52:56 -0400 Message-Id: <20201016045258.16246-3-dgilbert@interlog.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20201016045258.16246-1-dgilbert@interlog.com> References: <20201016045258.16246-1-dgilbert@interlog.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Both the SCSI and NVMe subsystems receive user data from the block layer in scatterlist_s (aka scatter gather lists (sgl) which are often arrays). If drivers in those subsystems represent storage (e.g. a ramdisk) or cache "hot" user data then they may also choose to use scatterlist_s. Currently there are no sgl to sgl operations in the kernel. Start with a copy. Signed-off-by: Douglas Gilbert --- include/linux/scatterlist.h | 4 ++ lib/scatterlist.c | 86 +++++++++++++++++++++++++++++++++++++ 2 files changed, 90 insertions(+) diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h index 80178afc2a4a..6649414c0749 100644 --- a/include/linux/scatterlist.h +++ b/include/linux/scatterlist.h @@ -321,6 +321,10 @@ size_t sg_pcopy_to_buffer(struct scatterlist *sgl, unsigned int nents, size_t sg_zero_buffer(struct scatterlist *sgl, unsigned int nents, size_t buflen, off_t skip); +size_t sgl_copy_sgl(struct scatterlist *d_sgl, unsigned int d_nents, off_t d_skip, + struct scatterlist *s_sgl, unsigned int s_nents, off_t s_skip, + size_t n_bytes); + /* * Maximum number of entries that will be allocated in one piece, if * a list larger than this is required then chaining will be utilized. diff --git a/lib/scatterlist.c b/lib/scatterlist.c index d5770e7f1030..1ec2c909c8d4 100644 --- a/lib/scatterlist.c +++ b/lib/scatterlist.c @@ -974,3 +974,89 @@ size_t sg_zero_buffer(struct scatterlist *sgl, unsigned int nents, return offset; } EXPORT_SYMBOL(sg_zero_buffer); + +/** + * sgl_copy_sgl - Copy over a destination sgl from a source sgl + * @d_sgl: Destination sgl + * @d_nents: Number of SG entries in destination sgl + * @d_skip: Number of bytes to skip in destination before copying + * @s_sgl: Source sgl + * @s_nents: Number of SG entries in source sgl + * @s_skip: Number of bytes to skip in source before copying + * @n_bytes: The number of bytes to copy + * + * Returns the number of copied bytes. + * + * Notes: + * Destination arguments appear before the source arguments, as with memcpy(). + * + * Stops copying if the end of d_sgl or s_sgl is reached. + * + * Since memcpy() is used, overlapping copies (where d_sgl and s_sgl belong + * to the same sgl and the copy regions overlap) are not supported. + * + * If d_skip is large, potentially spanning multiple d_nents then some + * integer arithmetic to adjust d_sgl may improve performance. For example + * if d_sgl is built using sgl_alloc_order(chainable=false) then the sgl + * will be an array with equally sized segments facilitating that + * arithmetic. The suggestion applies to s_skip, s_sgl and s_nents as well. + * + **/ +size_t sgl_copy_sgl(struct scatterlist *d_sgl, unsigned int d_nents, off_t d_skip, + struct scatterlist *s_sgl, unsigned int s_nents, off_t s_skip, + size_t n_bytes) +{ + size_t d_off, s_off, len, d_len, s_len; + size_t offset = 0; + struct sg_mapping_iter d_iter; + struct sg_mapping_iter s_iter; + + if (n_bytes == 0) + return 0; + sg_miter_start(&d_iter, d_sgl, d_nents, SG_MITER_ATOMIC | SG_MITER_TO_SG); + sg_miter_start(&s_iter, s_sgl, s_nents, SG_MITER_ATOMIC | SG_MITER_FROM_SG); + if (!sg_miter_skip(&d_iter, d_skip)) + goto fini; + if (!sg_miter_skip(&s_iter, s_skip)) + goto fini; + + for (d_off = 0, s_off = 0; true ; ) { + /* Assume d_iter.length and s_iter.length can never be 0 */ + if (d_off == 0) { + if (!sg_miter_next(&d_iter)) + break; + d_len = d_iter.length; + } else { + d_len = d_iter.length - d_off; + } + if (s_off == 0) { + if (!sg_miter_next(&s_iter)) + break; + s_len = s_iter.length; + } else { + s_len = s_iter.length - s_off; + } + len = min3(d_len, s_len, n_bytes - offset); + + memcpy(d_iter.addr + d_off, s_iter.addr + s_off, len); + offset += len; + if (offset >= n_bytes) + break; + if (d_len == s_len) { + d_off = 0; + s_off = 0; + } else if (d_len < s_len) { + d_off = 0; + s_off += len; + } else { + d_off += len; + s_off = 0; + } + } +fini: + sg_miter_stop(&d_iter); + sg_miter_stop(&s_iter); + return offset; +} +EXPORT_SYMBOL(sgl_copy_sgl); +