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 lists.sourceforge.net (lists.sourceforge.net [216.105.38.7]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 91658C433EF for ; Fri, 22 Jul 2022 16:32:10 +0000 (UTC) Received: from [127.0.0.1] (helo=sfs-ml-2.v29.lw.sourceforge.com) by sfs-ml-2.v29.lw.sourceforge.com with esmtp (Exim 4.94.2) (envelope-from ) id 1oEvZQ-0002Z0-Rn; Fri, 22 Jul 2022 16:32:09 +0000 Received: from [172.30.20.202] (helo=mx.sourceforge.net) by sfs-ml-2.v29.lw.sourceforge.com with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1oEvZP-0002Yq-Ec for linux-f2fs-devel@lists.sourceforge.net; Fri, 22 Jul 2022 16:32:08 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sourceforge.net; s=x; h=In-Reply-To:Content-Type:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=YMZXhtdn5M+niJZekRMW4NeTx5pyKfvMG6mIilAHpIM=; b=CWTD6lb3dHz7ag+JrmVo39Bl/C GCBcugCmcoRserfLHi+m8lu7BH6mTmIu2ag7NgY6UGsRYRawwgh+S52VuIa0/8t6BAVPkqfAkLGoz pYmwBhRGG+/Sv9Lurwcbc2DyH+9lpi7CF98tox6DQA4MlgS4YWzzG/mE9Cgiji2Sku4E=; DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sf.net; s=x ; h=In-Reply-To:Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To :From:Date:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=YMZXhtdn5M+niJZekRMW4NeTx5pyKfvMG6mIilAHpIM=; b=PmKQtLFNTYWsp2krZJT6XFKctL 65w72eCZrAAEUyOy9G7HczyMWOWNJ42a0FW5Q3uARa3/HVyLCTMi4dG0EmLCKrWRRcP1exjNa/bBH ZvcPJGkCCwMhYU5sPqEr1C8wP8yGy3BYEpElr/Diqy4fzCgmgkeDG7AURg1T04GhLQhc=; Received: from ams.source.kernel.org ([145.40.68.75]) by sfi-mx-2.v28.lw.sourceforge.com with esmtps (TLS1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.94.2) id 1oEvZL-0001Py-L7 for linux-f2fs-devel@lists.sourceforge.net; Fri, 22 Jul 2022 16:32:08 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id B9AD9B8296E for ; Fri, 22 Jul 2022 16:31:51 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 682F5C341C6; Fri, 22 Jul 2022 16:31:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1658507510; bh=2zJKttnRhj1+bfpQ1neKDFu0IlRxRblBoec0bp8Sdok=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=R6uxrMTGkXqjhGQr3zA8qNa8GSPQYWhhd4mQ3yYrU74pGY1LX1IaIR5hc0nNP92LQ q9wz+Ac3IrLVRoZlFBxpRSiQx2lr3niXhLmKlEKd0WaePq36/63ztLdxUHKVP91cna iTiD0U+7tuK8NQRrlnfsoyqCoOVisiWxoj95uBcTC6TpEN1dPCJvAwk4AG+OLFbipY Ev1zg3asT7LDP81fPvnsbpQUSyN9RHHDGbrlF5ehxKVjBYDOL18hUhi2yOduvU0hdK zkACGw2vJii36YKdGWHobF9F/E/t5jlN1+H172Y6t7CaMxCzV8c30PiPug7zXwMxcb 86mtOuQB7uKRA== Date: Fri, 22 Jul 2022 09:31:49 -0700 From: "Darrick J. Wong" To: Eric Biggers Message-ID: References: <20220722074229.148925-1-ebiggers@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20220722074229.148925-1-ebiggers@kernel.org> X-Headers-End: 1oEvZL-0001Py-L7 Subject: Re: [f2fs-dev] [man-pages RFC PATCH v2] statx.2, open.2: document STATX_DIOALIGN X-BeenThere: linux-f2fs-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-man@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-xfs@vger.kernel.org, Keith Busch , linux-fscrypt@vger.kernel.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net On Fri, Jul 22, 2022 at 12:42:28AM -0700, Eric Biggers wrote: > From: Eric Biggers > > Document the proposed STATX_DIOALIGN support for statx() > (https://lore.kernel.org/linux-fsdevel/20220722071228.146690-1-ebiggers@kernel.org/T/#u). > > Signed-off-by: Eric Biggers > --- > > v2: rebased onto man-pages master branch, mentioned xfs, and updated > link to patchset > > man2/open.2 | 43 ++++++++++++++++++++++++++++++++----------- > man2/statx.2 | 29 +++++++++++++++++++++++++++++ > 2 files changed, 61 insertions(+), 11 deletions(-) > > diff --git a/man2/open.2 b/man2/open.2 > index d1485999f..ef29847c3 100644 > --- a/man2/open.2 > +++ b/man2/open.2 > @@ -1732,21 +1732,42 @@ of user-space buffers and the file offset of I/Os. > In Linux alignment > restrictions vary by filesystem and kernel version and might be > absent entirely. > -However there is currently no filesystem\-independent > -interface for an application to discover these restrictions for a given > -file or filesystem. > -Some filesystems provide their own interfaces > -for doing so, for example the > +The handling of misaligned > +.B O_DIRECT > +I/Os also varies; they can either fail with > +.B EINVAL > +or fall back to buffered I/O. > +.PP > +Since Linux 5.20, > +.B O_DIRECT > +support and alignment restrictions for a file can be queried using > +.BR statx (2), > +using the > +.B STATX_DIOALIGN > +flag. > +Support for > +.B STATX_DIOALIGN > +varies by filesystem; see > +.BR statx (2). > +.PP > +Some filesystems provide their own interfaces for querying > +.B O_DIRECT > +alignment restrictions, for example the > .B XFS_IOC_DIOINFO > operation in > .BR xfsctl (3). > +.B STATX_DIOALIGN > +should be used instead when it is available. > .PP > -Under Linux 2.4, transfer sizes, the alignment of the user buffer, > -and the file offset must all be multiples of the logical block size > -of the filesystem. > -Since Linux 2.6.0, alignment to the logical block size of the > -underlying storage (typically 512 bytes) suffices. > -The logical block size can be determined using the > +If none of the above is available, then direct I/O support and alignment > +restrictions can only be assumed from known characteristics of the filesystem, > +the individual file, the underlying storage device(s), and the kernel version. > +In Linux 2.4, most block device based filesystems require that the file offset > +and the length and memory address of all I/O segments be multiples of the > +filesystem block size (typically 4096 bytes). > +In Linux 2.6.0, this was relaxed to the logical block size of the block device > +(typically 512 bytes). > +A block device's logical block size can be determined using the > .BR ioctl (2) > .B BLKSSZGET > operation or from the shell using the command: > diff --git a/man2/statx.2 b/man2/statx.2 > index 0326e9af0..ea38ec829 100644 > --- a/man2/statx.2 > +++ b/man2/statx.2 > @@ -61,7 +61,12 @@ struct statx { > containing the filesystem where the file resides */ > __u32 stx_dev_major; /* Major ID */ > __u32 stx_dev_minor; /* Minor ID */ > + > __u64 stx_mnt_id; /* Mount ID */ > + > + /* Direct I/O alignment restrictions */ > + __u32 stx_dio_mem_align; > + __u32 stx_dio_offset_align; > }; > .EE > .in > @@ -247,6 +252,8 @@ STATX_BTIME Want stx_btime > STATX_ALL The same as STATX_BASIC_STATS | STATX_BTIME. > It is deprecated and should not be used. > STATX_MNT_ID Want stx_mnt_id (since Linux 5.8) > +STATX_DIOALIGN Want stx_dio_mem_align and stx_dio_offset_align > + (since Linux 5.20; support varies by filesystem) > .TE > .in > .PP > @@ -407,6 +414,28 @@ This is the same number reported by > .BR name_to_handle_at (2) > and corresponds to the number in the first field in one of the records in > .IR /proc/self/mountinfo . > +.TP > +.I stx_dio_mem_align > +The alignment (in bytes) required for user memory buffers for direct I/O > +.BR "" ( O_DIRECT ) > +on this file. or 0 if direct I/O is not supported on this file. Nit: "..on this file, or 0 if direct..." > +.IP > +.B STATX_DIOALIGN > +.IR "" ( stx_dio_mem_align > +and > +.IR stx_dio_offset_align ) > +is supported on block devices since Linux 5.20. > +The support on regular files varies by filesystem; it is supported by ext4, > +f2fs, and xfs since Linux 5.20. > +.TP > +.I stx_dio_offset_align > +The alignment (in bytes) required for file offsets and I/O segment lengths for > +direct I/O > +.BR "" ( O_DIRECT ) > +on this file, or 0 if direct I/O is not supported on this file. On this last part -- userspace can only conclude that directio is not supported on the file if ((STATX_DIOALIGN & stx_mask) && stx_dio_offset_align == 0), right? IOWs, if (STATX_DIOALIGN & stx_mask)==0 then userspace can't draw any conclusions from stx_dio_offset_align, correct? If the answers are yes and yes, then I think I've understood all this and can say Reviewed-by: Darrick J. Wong --D > +This will only be nonzero if > +.I stx_dio_mem_align > +is nonzero, and vice versa. > .PP > For further information on the above fields, see > .BR inode (7). > > base-commit: f9f25914e4ed393ac284ab921876e8a78722c504 > -- > 2.37.0 > _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel