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| author | Christoph Hellwig <hch@lst.de> | 2025-04-08 07:54:12 -0700 |
|---|---|---|
| committer | Darrick J. Wong <djwong@kernel.org> | 2025-04-08 07:54:28 -0700 |
| commit | b54ac15f578a7813b5f798e111de8e136f633c7e (patch) | |
| tree | a4850eb52c95375540a5adea7443f5344c0df1cb /design/XFS_Filesystem_Structure | |
| parent | e271e0a698d6f6f3d826ca9678305336705d9841 (diff) | |
| download | xfs-documentation-b54ac15f578a7813b5f798e111de8e136f633c7e.tar.gz | |
design: document the zoned on-disk format
Document the feature flags, superblock fields and new dinode union.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Diffstat (limited to 'design/XFS_Filesystem_Structure')
| -rw-r--r-- | design/XFS_Filesystem_Structure/ondisk_inode.asciidoc | 13 | ||||
| -rw-r--r-- | design/XFS_Filesystem_Structure/realtime.asciidoc | 34 | ||||
| -rw-r--r-- | design/XFS_Filesystem_Structure/superblock.asciidoc | 25 |
3 files changed, 71 insertions, 1 deletions
diff --git a/design/XFS_Filesystem_Structure/ondisk_inode.asciidoc b/design/XFS_Filesystem_Structure/ondisk_inode.asciidoc index ab4a503..ba111eb 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 1664152..c767489 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. When an external +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 f045530..bd34eb0 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: |