From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 11C1022A1F1 for ; Thu, 20 Mar 2025 20:40:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742503228; cv=none; b=f838a9f+G4E530KBJKtV9FPwQtiNsAfttjDWmtGswymLQ7r8ceHK54x7Rl+CV7pqbCXyihxFz1qeEAwgSah6xCVmQVuhOZPNJpb7TdaJxCZdla66jCfuinu9z5jHnaiNxjylXFgH2iQJQdWxsOwDpPqxHtPuHKYbLgF3d17E/Gs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742503228; c=relaxed/simple; bh=r7fKqh3ha/8+KYZC6xa3BoMX05xUOSODsqMhTwzsdfM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=J9cBAKNeuJebqvNWTgecVwgsEDzbIEHiwW0mQelFmFAtS/FW7WAtS7cXoK0w/y1ZFDHjFe1j+oGC3Wriuhd7IFXM3lr6jdM5u5EYollk5T2fhadqSg177lfRirm0Yqxfh7usPXZPyd/z0NVgBGO5H0hIsYKS28s1bwMfCMPz5RA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ZOWYqzvg; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ZOWYqzvg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D5087C4CEDD; Thu, 20 Mar 2025 20:40:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1742503227; bh=r7fKqh3ha/8+KYZC6xa3BoMX05xUOSODsqMhTwzsdfM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ZOWYqzvg4HL3dnofUtsjt5Z7tdB8uKAZhb08ZjqM9jdIkHWIY8FY+zqTlUvkl5Ehn 2Lw2Zz62hpk/eRGTF2tiI3JOMRgKVEeSXWBqPnLYkZgAGaL3s8evBuA+2aCt8U8hTN hT205fqVmo3rCaCOece/jSAIIAojI4fdYqaayY5EjIaCxCW91msPnZdN1YRGI2U5eI /5r97LKKgFIsbZtTjJ0lgGaKt4n2PUlzqCxvwqMa5fZFDTtUMKNMUOyeAFJ4Gpw2og E3a87PDz6Ry4hH45xH4106pQMbIzXFdmaQUogVaFFVTv4W9SzYciuo96fsRXznoWcI vq1VLsonXib1g== Date: Thu, 20 Mar 2025 13:40:27 -0700 From: "Darrick J. Wong" To: Christoph Hellwig Cc: linux-xfs@vger.kernel.org, Hans.Holmberg@wdc.com Subject: Re: [PATCH] design: document the zoned on-disk format Message-ID: <20250320204027.GE2803749@frogsfrogsfrogs> References: <20250320160541.1635550-1-hch@lst.de> Precedence: bulk X-Mailing-List: linux-xfs@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: <20250320160541.1635550-1-hch@lst.de> On Thu, Mar 20, 2025 at 05:05:41PM +0100, Christoph Hellwig wrote: > Document the feature flags, superblock fields and new dinode union. > > Signed-off-by: Christoph Hellwig > --- > .../ondisk_inode.asciidoc | 13 ++++++- > .../realtime.asciidoc | 34 +++++++++++++++++++ > .../superblock.asciidoc | 25 ++++++++++++++ > 3 files changed, 71 insertions(+), 1 deletion(-) > > diff --git a/design/XFS_Filesystem_Structure/ondisk_inode.asciidoc b/design/XFS_Filesystem_Structure/ondisk_inode.asciidoc > index ab4a503b4da6..ba111ebe6e3a 100644 > --- a/design/XFS_Filesystem_Structure/ondisk_inode.asciidoc > +++ b/design/XFS_Filesystem_Structure/ondisk_inode.asciidoc > @@ -139,7 +139,10 @@ struct xfs_dinode_core { > __be64 di_changecount; > __be64 di_lsn; > __be64 di_flags2; > - __be32 di_cowextsize; > + union { > + __be32 di_cowextsize; > + __be32 di_used_blocks; > + }; > __u8 di_pad2[12]; > xfs_timestamp_t di_crtime; > __be64 di_ino; > @@ -425,6 +428,14 @@ the source file to the destination file if the sharing operation completely > overwrites the destination file's contents and the destination file does not > already have +di_cowextsize+ set. > > +*di_used_blocks*:: > + > +Used only for the xref:Real_time_Reverse_Mapping_Btree[Reverse-Mapping B+tree] > +inode on filesystems with a xref:Zoned[Zoned Real-time Device]. Tracks the > +number of filesystem blocks in the rtgroup that have been written but not > +unmapped, i.e. the number of blocks that are referenced by at least one rmap > +entry. > + > *di_pad2*:: > Padding for future expansion of the inode. > > diff --git a/design/XFS_Filesystem_Structure/realtime.asciidoc b/design/XFS_Filesystem_Structure/realtime.asciidoc > index 16641525e201..fff0f691594a 100644 > --- a/design/XFS_Filesystem_Structure/realtime.asciidoc > +++ b/design/XFS_Filesystem_Structure/realtime.asciidoc > @@ -397,3 +397,37 @@ meta_uuid = 7e55b909-8728-4d69-a1fa-891427314eea > include::rtrmapbt.asciidoc[] > > include::rtrefcountbt.asciidoc[] > + > +[[Zoned]] > +== Zoned Real-time Devices > + > +If the +XFS_SB_FEAT_INCOMPAT_ZONED+ feature is enabled, the real time device > +uses an entirely different space allocator. This features does not use the > +xref:Real-Time_Bitmap_Inode[Free Space Bitmap Inode] and > +xref:Real-Time_Summary_Inode[Free Space Summary Inode]. > +Instead, writes to the storage hardware must always occur sequentially > +from the start to the end of a rtgroup. To support this requirement, > +file data are always written out of place using the so called copy on write > +or COW write path (which actually just redirects on write and never copies). > + > +When an rtgroup runs out of space to write, free space is reclaimed by > +copying and remapping still valid data from the full rtgroups into > +another rtgroup. Once the rtgroup is empty, it is written to from the > +beginning again. For this, the > +xref:Real_time_Reverse_Mapping_Btree[Reverse-Mapping B+tree] is required. > + > +For storage hardware that supports hardware zones, each rtgroup is mapped > +to exactly one zone. When a file system is created on a a zoned storage > +device that does support conventional (aka random writable) zones at the > +beginning of the LBA space, those zones are used for the xfs data device > +(which in this case is primarily used for metadata), and the zoned requiring > +sequential writes are presented as the real-time device. But when an external Dumb nit: sentence doesn't need to begin with "But", e.g. "When an external real-time device is used..." Otherwise I think this description matches what I saw in the kernel changes so with that one silly nit fixed, Reviewed-by: "Darrick J. Wong" Actually, wait, I'm the maintainer of xfs-docs. I'll fix it on commit if there isn't a v2 in the next week or so. --D > +real-time device is used, rtgroups might also map to conventional zones. > + > +Filesystems with a zoned real-time device by default use the real-time device > +for all data, and the data device only for metadata, which makes the > +terminology a bit confusing. But this is merely the default setting. Like > +any other filesystem with a realtime volume, the +XFS_DIFLAG_REALTIME+ flag > +can be cleared on an empty regular file to target the data device; and the > ++XFS_DIFLAG_RTINHERIT+ flag can be cleared on a directory so that new > +children will target the data device." > diff --git a/design/XFS_Filesystem_Structure/superblock.asciidoc b/design/XFS_Filesystem_Structure/superblock.asciidoc > index f04553046357..bd34eb0d3066 100644 > --- a/design/XFS_Filesystem_Structure/superblock.asciidoc > +++ b/design/XFS_Filesystem_Structure/superblock.asciidoc > @@ -74,6 +74,8 @@ struct xfs_dsb { > __be32 sb_rgextents; > __u8 sb_rgblklog; > __u8 sb_pad[7]; > + __be64 sb_rtstart; > + __be64 sb_rtreserved; > > /* must be padded to 64 bit alignment */ > }; > @@ -449,6 +451,16 @@ pointers] for more information. > Metadata directory tree. See the section about the xref:Metadata_Directories[ > metadata directory tree] for more information. > > +| +XFS_SB_FEAT_INCOMPAT_ZONED+ | > +Zoned RT device. See the section about the xref:Zoned[Zoned Real-time Devices] > +for more information. > + > +| +XFS_SB_FEAT_INCOMPAT_ZONE_GAPS+ | > +Each hardware zone has unusable space at the end of its LBA range, which is > +mirrored by unusable filesystem blocks at the end of the rtgroup. The > ++xfs_rtblock_t startblock+ in file mappings is linearly mapped to the > +hardware LBA space. > + > |===== > > *sb_features_log_incompat*:: > @@ -505,6 +517,19 @@ generate absolute block numbers defined in extent maps from the segmented > *sb_pad[7]*:: > Zeroes, if the +XFS_SB_FEAT_RO_INCOMPAT_METADIR+ feature is enabled. > > +*sb_rtstart*:: > + > +If the +XFS_SB_FEAT_INCOMPAT_ZONED+ feature is enabled, this is the start > +of the internal RT section. That is the RT section is placed on the same > +device as the data device, and starts at this offset into the device. > +The value is in units of file system blocks. > + > +*sb_rtreserved*:: > + > +If the +XFS_SB_FEAT_INCOMPAT_ZONED+ feature is enabled, this is the amount > +of space in the realtime section that is reserved for internal use > +by garbage collection and reorganization algorithms. > + > === xfs_db Superblock Example > > A filesystem is made on a single disk with the following command: > -- > 2.45.2 > >