From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8D81DE81E1B for ; Fri, 6 Oct 2023 18:15:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233202AbjJFSP0 (ORCPT ); Fri, 6 Oct 2023 14:15:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38264 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233088AbjJFSPZ (ORCPT ); Fri, 6 Oct 2023 14:15:25 -0400 Received: from mail-yb1-xb35.google.com (mail-yb1-xb35.google.com [IPv6:2607:f8b0:4864:20::b35]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C7AE7BF for ; Fri, 6 Oct 2023 11:15:23 -0700 (PDT) Received: by mail-yb1-xb35.google.com with SMTP id 3f1490d57ef6-d865854ef96so2596983276.2 for ; Fri, 06 Oct 2023 11:15:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1696616122; x=1697220922; darn=vger.kernel.org; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=AYLhV8RKvbCInhnzqZ/HGBAbLzuMZXeZ10wGn+QIDt0=; b=agZMnV/HJlJNR+eXnUqkrCNrnhdt8cTuH8KPxM8I0UlHzDgSB7yZOnfEzjuFFKmcys px5mNgUlWMDvOhhIQ0tlHY+8PJ6lEWdjJPSApcLl/imzQggHqLnKYP1xPJpvbKX7Pxv/ 8kR/kNwBWBPMQjEU7AXu3y2seqJXmjp4CTdY4oB1MHnwBAD2awuAUZPZnHR4vh0brRey GhZvL/kPa8oQLPzBPzQ1kfkPRDz7LJIeNOKK/15bFxj9KCs7KIWsjDEqTIHOSh+IwdEf ag4eZsxXhkYwVL5qydQ7mcnxfV/I44GhPcxTxAOWs1vxEnC+e8YwG+HGK+zixX8m9djt T7vA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1696616122; x=1697220922; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=AYLhV8RKvbCInhnzqZ/HGBAbLzuMZXeZ10wGn+QIDt0=; b=Zlss3wMtDB103+Pgmgk8yafbGr6AN7YHmU0W/jsbLlpiJokhd0vrKg6pQhauWyEP4w g9q+X1I+C3l6yvNNLp3BCUX6BWigOHCcDS5YRotzrcK8x0Mx4PlLytljHxtW4tOAF0LZ 1KfmIdPfIksWZJfY1OJEQKreEDpukRaDWeUngp5w/adqKfthzjDTR8G39c001FdwnpuL KfWGVoPTh7Kf76XP53gAP9fa4S3O8xOQCTGVn/jev/FeynZrXJYZQgW3kbTU5+lCo3IH DdmDdKLIqMkH7ryA4zm6fbJ+sm/We0RXryPOA4PCqrv0aPPHB/8ruxWBHTpZtCuLZOcR ThWg== X-Gm-Message-State: AOJu0YyEBATdfCOwUYd0CbyLzBVIJduHY7DBDIq3VG6U7q33vhFnUyP7 YP2tDZhbwZOds9Sr+O4tshpcj5UpZJ+2ijdVor+ptA== X-Google-Smtp-Source: AGHT+IHzqypY4NdUT7zu05+MFHgfnxNiLO+3lSgUozk3D6Rhta9XqDneUgYhohjCWFkKwZkcLQmr90WO9qHqGTSh0Io= X-Received: by 2002:a25:509:0:b0:d7f:cdc8:e184 with SMTP id 9-20020a250509000000b00d7fcdc8e184mr8607707ybf.49.1696616122514; Fri, 06 Oct 2023 11:15:22 -0700 (PDT) MIME-Version: 1.0 References: <20230929102726.2985188-1-john.g.garry@oracle.com> <20230929102726.2985188-5-john.g.garry@oracle.com> In-Reply-To: <20230929102726.2985188-5-john.g.garry@oracle.com> From: Jeremy Bongio Date: Fri, 6 Oct 2023 11:15:11 -0700 Message-ID: Subject: Re: [PATCH 04/21] fs: Add RWF_ATOMIC and IOCB_ATOMIC flags for atomic write support To: John Garry Cc: axboe@kernel.dk, kbusch@kernel.org, hch@lst.de, sagi@grimberg.me, jejb@linux.ibm.com, martin.petersen@oracle.com, djwong@kernel.org, viro@zeniv.linux.org.uk, brauner@kernel.org, chandan.babu@oracle.com, dchinner@redhat.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, tytso@mit.edu, linux-api@vger.kernel.org, Prasad Singamsetty Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org What is the advantage of using write flags instead of using an atomic open flag (O_ATOMIC)? With an open flag, write, writev, pwritev would all be supported for atomic writes. And this would potentially require less application changes to take advantage of atomic writes. On Fri, Sep 29, 2023 at 3:28=E2=80=AFAM John Garry wrote: > > From: Prasad Singamsetty > > Userspace may add flag RWF_ATOMIC to pwritev2() to indicate that the > write is to be issued with torn write prevention, according to special > alignment and length rules. > > Torn write prevention means that for a power or any other HW failure, all > or none of the data will be committed to storage, but never a mix of old > and new. > > For any syscall interface utilizing struct iocb, add IOCB_ATOMIC for > iocb->ki_flags field to indicate the same. > > A call to statx will give the relevant atomic write info: > - atomic_write_unit_min > - atomic_write_unit_max > > Both values are a power-of-2. > > Applications can avail of atomic write feature by ensuring that the total > length of a write is a power-of-2 in size and also sized between > atomic_write_unit_min and atomic_write_unit_max, inclusive. Applications > must ensure that the write is at a naturally-aligned offset in the file > wrt the total write length. > > Signed-off-by: Prasad Singamsetty > Signed-off-by: John Garry > --- > include/linux/fs.h | 1 + > include/uapi/linux/fs.h | 5 ++++- > 2 files changed, 5 insertions(+), 1 deletion(-) > > diff --git a/include/linux/fs.h b/include/linux/fs.h > index b528f063e8ff..898952dee8eb 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -328,6 +328,7 @@ enum rw_hint { > #define IOCB_SYNC (__force int) RWF_SYNC > #define IOCB_NOWAIT (__force int) RWF_NOWAIT > #define IOCB_APPEND (__force int) RWF_APPEND > +#define IOCB_ATOMIC (__force int) RWF_ATOMIC > > /* non-RWF related bits - start at 16 */ > #define IOCB_EVENTFD (1 << 16) > diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h > index b7b56871029c..e3b4f5bc6860 100644 > --- a/include/uapi/linux/fs.h > +++ b/include/uapi/linux/fs.h > @@ -301,8 +301,11 @@ typedef int __bitwise __kernel_rwf_t; > /* per-IO O_APPEND */ > #define RWF_APPEND ((__force __kernel_rwf_t)0x00000010) > > +/* Atomic Write */ > +#define RWF_ATOMIC ((__force __kernel_rwf_t)0x00000020) > + > /* mask of flags supported by the kernel */ > #define RWF_SUPPORTED (RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT |\ > - RWF_APPEND) > + RWF_APPEND | RWF_ATOMIC) > > #endif /* _UAPI_LINUX_FS_H */ > -- > 2.31.1 >