^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 1) .. SPDX-License-Identifier: GPL-2.0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 2)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 3) ================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 4) ZoneFS - Zone filesystem for Zoned block devices
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 5) ================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 6)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 7) Introduction
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 8) ============
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 9)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10) zonefs is a very simple file system exposing each zone of a zoned block device
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11) as a file. Unlike a regular POSIX-compliant file system with native zoned block
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12) device support (e.g. f2fs), zonefs does not hide the sequential write
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13) constraint of zoned block devices to the user. Files representing sequential
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14) write zones of the device must be written sequentially starting from the end
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15) of the file (append only writes).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17) As such, zonefs is in essence closer to a raw block device access interface
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18) than to a full-featured POSIX file system. The goal of zonefs is to simplify
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19) the implementation of zoned block device support in applications by replacing
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20) raw block device file accesses with a richer file API, avoiding relying on
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21) direct block device file ioctls which may be more obscure to developers. One
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22) example of this approach is the implementation of LSM (log-structured merge)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23) tree structures (such as used in RocksDB and LevelDB) on zoned block devices
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24) by allowing SSTables to be stored in a zone file similarly to a regular file
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25) system rather than as a range of sectors of the entire disk. The introduction
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26) of the higher level construct "one file is one zone" can help reducing the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27) amount of changes needed in the application as well as introducing support for
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) different application programming languages.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30) Zoned block devices
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31) -------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33) Zoned storage devices belong to a class of storage devices with an address
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 34) space that is divided into zones. A zone is a group of consecutive LBAs and all
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 35) zones are contiguous (there are no LBA gaps). Zones may have different types.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 36)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 37) * Conventional zones: there are no access constraints to LBAs belonging to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 38) conventional zones. Any read or write access can be executed, similarly to a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 39) regular block device.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 40) * Sequential zones: these zones accept random reads but must be written
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 41) sequentially. Each sequential zone has a write pointer maintained by the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 42) device that keeps track of the mandatory start LBA position of the next write
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 43) to the device. As a result of this write constraint, LBAs in a sequential zone
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 44) cannot be overwritten. Sequential zones must first be erased using a special
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 45) command (zone reset) before rewriting.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 46)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 47) Zoned storage devices can be implemented using various recording and media
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 48) technologies. The most common form of zoned storage today uses the SCSI Zoned
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 49) Block Commands (ZBC) and Zoned ATA Commands (ZAC) interfaces on Shingled
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 50) Magnetic Recording (SMR) HDDs.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 51)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 52) Solid State Disks (SSD) storage devices can also implement a zoned interface
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 53) to, for instance, reduce internal write amplification due to garbage collection.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 54) The NVMe Zoned NameSpace (ZNS) is a technical proposal of the NVMe standard
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 55) committee aiming at adding a zoned storage interface to the NVMe protocol.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 56)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 57) Zonefs Overview
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 58) ===============
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 59)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 60) Zonefs exposes the zones of a zoned block device as files. The files
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 61) representing zones are grouped by zone type, which are themselves represented
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 62) by sub-directories. This file structure is built entirely using zone information
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 63) provided by the device and so does not require any complex on-disk metadata
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 64) structure.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 65)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 66) On-disk metadata
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 67) ----------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 68)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 69) zonefs on-disk metadata is reduced to an immutable super block which
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 70) persistently stores a magic number and optional feature flags and values. On
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 71) mount, zonefs uses blkdev_report_zones() to obtain the device zone configuration
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 72) and populates the mount point with a static file tree solely based on this
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 73) information. File sizes come from the device zone type and write pointer
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 74) position managed by the device itself.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 75)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 76) The super block is always written on disk at sector 0. The first zone of the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 77) device storing the super block is never exposed as a zone file by zonefs. If
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 78) the zone containing the super block is a sequential zone, the mkzonefs format
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 79) tool always "finishes" the zone, that is, it transitions the zone to a full
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 80) state to make it read-only, preventing any data write.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 81)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 82) Zone type sub-directories
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 83) -------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 84)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 85) Files representing zones of the same type are grouped together under the same
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 86) sub-directory automatically created on mount.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 87)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 88) For conventional zones, the sub-directory "cnv" is used. This directory is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 89) however created if and only if the device has usable conventional zones. If
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 90) the device only has a single conventional zone at sector 0, the zone will not
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 91) be exposed as a file as it will be used to store the zonefs super block. For
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 92) such devices, the "cnv" sub-directory will not be created.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 93)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 94) For sequential write zones, the sub-directory "seq" is used.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 95)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 96) These two directories are the only directories that exist in zonefs. Users
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 97) cannot create other directories and cannot rename nor delete the "cnv" and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 98) "seq" sub-directories.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 99)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 100) The size of the directories indicated by the st_size field of struct stat,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 101) obtained with the stat() or fstat() system calls, indicates the number of files
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 102) existing under the directory.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 103)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 104) Zone files
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 105) ----------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 106)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 107) Zone files are named using the number of the zone they represent within the set
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 108) of zones of a particular type. That is, both the "cnv" and "seq" directories
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 109) contain files named "0", "1", "2", ... The file numbers also represent
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 110) increasing zone start sector on the device.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 111)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 112) All read and write operations to zone files are not allowed beyond the file
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 113) maximum size, that is, beyond the zone capacity. Any access exceeding the zone
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 114) capacity is failed with the -EFBIG error.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 115)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 116) Creating, deleting, renaming or modifying any attribute of files and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 117) sub-directories is not allowed.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 118)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 119) The number of blocks of a file as reported by stat() and fstat() indicates the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 120) capacity of the zone file, or in other words, the maximum file size.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 121)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 122) Conventional zone files
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 123) -----------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 124)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 125) The size of conventional zone files is fixed to the size of the zone they
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 126) represent. Conventional zone files cannot be truncated.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 127)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 128) These files can be randomly read and written using any type of I/O operation:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 129) buffered I/Os, direct I/Os, memory mapped I/Os (mmap), etc. There are no I/O
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 130) constraint for these files beyond the file size limit mentioned above.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 131)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 132) Sequential zone files
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 133) ---------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 134)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 135) The size of sequential zone files grouped in the "seq" sub-directory represents
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 136) the file's zone write pointer position relative to the zone start sector.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 137)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 138) Sequential zone files can only be written sequentially, starting from the file
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 139) end, that is, write operations can only be append writes. Zonefs makes no
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 140) attempt at accepting random writes and will fail any write request that has a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 141) start offset not corresponding to the end of the file, or to the end of the last
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 142) write issued and still in-flight (for asynchronous I/O operations).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 143)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 144) Since dirty page writeback by the page cache does not guarantee a sequential
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 145) write pattern, zonefs prevents buffered writes and writeable shared mappings
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 146) on sequential files. Only direct I/O writes are accepted for these files.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 147) zonefs relies on the sequential delivery of write I/O requests to the device
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 148) implemented by the block layer elevator. An elevator implementing the sequential
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 149) write feature for zoned block device (ELEVATOR_F_ZBD_SEQ_WRITE elevator feature)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 150) must be used. This type of elevator (e.g. mq-deadline) is set by default
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 151) for zoned block devices on device initialization.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 152)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 153) There are no restrictions on the type of I/O used for read operations in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 154) sequential zone files. Buffered I/Os, direct I/Os and shared read mappings are
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 155) all accepted.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 156)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 157) Truncating sequential zone files is allowed only down to 0, in which case, the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 158) zone is reset to rewind the file zone write pointer position to the start of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 159) the zone, or up to the zone capacity, in which case the file's zone is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 160) transitioned to the FULL state (finish zone operation).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 161)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 162) Format options
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 163) --------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 164)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 165) Several optional features of zonefs can be enabled at format time.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 166)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 167) * Conventional zone aggregation: ranges of contiguous conventional zones can be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 168) aggregated into a single larger file instead of the default one file per zone.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 169) * File ownership: The owner UID and GID of zone files is by default 0 (root)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 170) but can be changed to any valid UID/GID.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 171) * File access permissions: the default 640 access permissions can be changed.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 172)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 173) IO error handling
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 174) -----------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 175)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 176) Zoned block devices may fail I/O requests for reasons similar to regular block
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 177) devices, e.g. due to bad sectors. However, in addition to such known I/O
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 178) failure pattern, the standards governing zoned block devices behavior define
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 179) additional conditions that result in I/O errors.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 180)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 181) * A zone may transition to the read-only condition (BLK_ZONE_COND_READONLY):
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 182) While the data already written in the zone is still readable, the zone can
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 183) no longer be written. No user action on the zone (zone management command or
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 184) read/write access) can change the zone condition back to a normal read/write
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 185) state. While the reasons for the device to transition a zone to read-only
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 186) state are not defined by the standards, a typical cause for such transition
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 187) would be a defective write head on an HDD (all zones under this head are
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 188) changed to read-only).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 189)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 190) * A zone may transition to the offline condition (BLK_ZONE_COND_OFFLINE):
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 191) An offline zone cannot be read nor written. No user action can transition an
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 192) offline zone back to an operational good state. Similarly to zone read-only
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 193) transitions, the reasons for a drive to transition a zone to the offline
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 194) condition are undefined. A typical cause would be a defective read-write head
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 195) on an HDD causing all zones on the platter under the broken head to be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 196) inaccessible.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 197)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 198) * Unaligned write errors: These errors result from the host issuing write
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 199) requests with a start sector that does not correspond to a zone write pointer
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 200) position when the write request is executed by the device. Even though zonefs
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 201) enforces sequential file write for sequential zones, unaligned write errors
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 202) may still happen in the case of a partial failure of a very large direct I/O
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 203) operation split into multiple BIOs/requests or asynchronous I/O operations.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 204) If one of the write request within the set of sequential write requests
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 205) issued to the device fails, all write requests queued after it will
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 206) become unaligned and fail.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 207)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 208) * Delayed write errors: similarly to regular block devices, if the device side
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 209) write cache is enabled, write errors may occur in ranges of previously
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 210) completed writes when the device write cache is flushed, e.g. on fsync().
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 211) Similarly to the previous immediate unaligned write error case, delayed write
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 212) errors can propagate through a stream of cached sequential data for a zone
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 213) causing all data to be dropped after the sector that caused the error.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 214)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 215) All I/O errors detected by zonefs are notified to the user with an error code
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 216) return for the system call that triggered or detected the error. The recovery
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 217) actions taken by zonefs in response to I/O errors depend on the I/O type (read
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 218) vs write) and on the reason for the error (bad sector, unaligned writes or zone
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 219) condition change).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 220)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 221) * For read I/O errors, zonefs does not execute any particular recovery action,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 222) but only if the file zone is still in a good condition and there is no
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 223) inconsistency between the file inode size and its zone write pointer position.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 224) If a problem is detected, I/O error recovery is executed (see below table).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 225)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 226) * For write I/O errors, zonefs I/O error recovery is always executed.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 227)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 228) * A zone condition change to read-only or offline also always triggers zonefs
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 229) I/O error recovery.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 230)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 231) Zonefs minimal I/O error recovery may change a file size and file access
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 232) permissions.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 233)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 234) * File size changes:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 235) Immediate or delayed write errors in a sequential zone file may cause the file
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 236) inode size to be inconsistent with the amount of data successfully written in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 237) the file zone. For instance, the partial failure of a multi-BIO large write
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 238) operation will cause the zone write pointer to advance partially, even though
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 239) the entire write operation will be reported as failed to the user. In such
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 240) case, the file inode size must be advanced to reflect the zone write pointer
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 241) change and eventually allow the user to restart writing at the end of the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 242) file.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 243) A file size may also be reduced to reflect a delayed write error detected on
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 244) fsync(): in this case, the amount of data effectively written in the zone may
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 245) be less than originally indicated by the file inode size. After such I/O
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 246) error, zonefs always fixes the file inode size to reflect the amount of data
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 247) persistently stored in the file zone.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 248)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 249) * Access permission changes:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 250) A zone condition change to read-only is indicated with a change in the file
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 251) access permissions to render the file read-only. This disables changes to the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 252) file attributes and data modification. For offline zones, all permissions
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 253) (read and write) to the file are disabled.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 254)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 255) Further action taken by zonefs I/O error recovery can be controlled by the user
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 256) with the "errors=xxx" mount option. The table below summarizes the result of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 257) zonefs I/O error processing depending on the mount option and on the zone
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 258) conditions::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 259)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 260) +--------------+-----------+-----------------------------------------+
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 261) | | | Post error state |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 262) | "errors=xxx" | device | access permissions |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 263) | mount | zone | file file device zone |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 264) | option | condition | size read write read write |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 265) +--------------+-----------+-----------------------------------------+
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 266) | | good | fixed yes no yes yes |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 267) | remount-ro | read-only | as is yes no yes no |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 268) | (default) | offline | 0 no no no no |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 269) +--------------+-----------+-----------------------------------------+
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 270) | | good | fixed yes no yes yes |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 271) | zone-ro | read-only | as is yes no yes no |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 272) | | offline | 0 no no no no |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 273) +--------------+-----------+-----------------------------------------+
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 274) | | good | 0 no no yes yes |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 275) | zone-offline | read-only | 0 no no yes no |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 276) | | offline | 0 no no no no |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 277) +--------------+-----------+-----------------------------------------+
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 278) | | good | fixed yes yes yes yes |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 279) | repair | read-only | as is yes no yes no |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 280) | | offline | 0 no no no no |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 281) +--------------+-----------+-----------------------------------------+
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 282)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 283) Further notes:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 284)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 285) * The "errors=remount-ro" mount option is the default behavior of zonefs I/O
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 286) error processing if no errors mount option is specified.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 287) * With the "errors=remount-ro" mount option, the change of the file access
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 288) permissions to read-only applies to all files. The file system is remounted
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 289) read-only.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 290) * Access permission and file size changes due to the device transitioning zones
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 291) to the offline condition are permanent. Remounting or reformatting the device
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 292) with mkfs.zonefs (mkzonefs) will not change back offline zone files to a good
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 293) state.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 294) * File access permission changes to read-only due to the device transitioning
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 295) zones to the read-only condition are permanent. Remounting or reformatting
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 296) the device will not re-enable file write access.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 297) * File access permission changes implied by the remount-ro, zone-ro and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 298) zone-offline mount options are temporary for zones in a good condition.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 299) Unmounting and remounting the file system will restore the previous default
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 300) (format time values) access rights to the files affected.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 301) * The repair mount option triggers only the minimal set of I/O error recovery
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 302) actions, that is, file size fixes for zones in a good condition. Zones
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 303) indicated as being read-only or offline by the device still imply changes to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 304) the zone file access permissions as noted in the table above.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 305)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 306) Mount options
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 307) -------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 308)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 309) zonefs define the "errors=<behavior>" mount option to allow the user to specify
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 310) zonefs behavior in response to I/O errors, inode size inconsistencies or zone
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 311) condition changes. The defined behaviors are as follow:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 312)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 313) * remount-ro (default)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 314) * zone-ro
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 315) * zone-offline
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 316) * repair
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 317)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 318) The run-time I/O error actions defined for each behavior are detailed in the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 319) previous section. Mount time I/O errors will cause the mount operation to fail.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 320) The handling of read-only zones also differs between mount-time and run-time.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 321) If a read-only zone is found at mount time, the zone is always treated in the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 322) same manner as offline zones, that is, all accesses are disabled and the zone
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 323) file size set to 0. This is necessary as the write pointer of read-only zones
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 324) is defined as invalib by the ZBC and ZAC standards, making it impossible to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 325) discover the amount of data that has been written to the zone. In the case of a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 326) read-only zone discovered at run-time, as indicated in the previous section.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 327) The size of the zone file is left unchanged from its last updated value.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 328)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 329) A zoned block device (e.g. an NVMe Zoned Namespace device) may have limits on
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 330) the number of zones that can be active, that is, zones that are in the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 331) implicit open, explicit open or closed conditions. This potential limitation
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 332) translates into a risk for applications to see write IO errors due to this
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 333) limit being exceeded if the zone of a file is not already active when a write
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 334) request is issued by the user.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 335)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 336) To avoid these potential errors, the "explicit-open" mount option forces zones
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 337) to be made active using an open zone command when a file is opened for writing
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 338) for the first time. If the zone open command succeeds, the application is then
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 339) guaranteed that write requests can be processed. Conversely, the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 340) "explicit-open" mount option will result in a zone close command being issued
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 341) to the device on the last close() of a zone file if the zone is not full nor
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 342) empty.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 343)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 344) Zonefs User Space Tools
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 345) =======================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 346)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 347) The mkzonefs tool is used to format zoned block devices for use with zonefs.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 348) This tool is available on Github at:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 349)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 350) https://github.com/damien-lemoal/zonefs-tools
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 351)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 352) zonefs-tools also includes a test suite which can be run against any zoned
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 353) block device, including null_blk block device created with zoned mode.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 354)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 355) Examples
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 356) --------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 357)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 358) The following formats a 15TB host-managed SMR HDD with 256 MB zones
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 359) with the conventional zones aggregation feature enabled::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 360)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 361) # mkzonefs -o aggr_cnv /dev/sdX
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 362) # mount -t zonefs /dev/sdX /mnt
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 363) # ls -l /mnt/
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 364) total 0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 365) dr-xr-xr-x 2 root root 1 Nov 25 13:23 cnv
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 366) dr-xr-xr-x 2 root root 55356 Nov 25 13:23 seq
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 367)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 368) The size of the zone files sub-directories indicate the number of files
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 369) existing for each type of zones. In this example, there is only one
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 370) conventional zone file (all conventional zones are aggregated under a single
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 371) file)::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 372)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 373) # ls -l /mnt/cnv
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 374) total 137101312
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 375) -rw-r----- 1 root root 140391743488 Nov 25 13:23 0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 376)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 377) This aggregated conventional zone file can be used as a regular file::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 378)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 379) # mkfs.ext4 /mnt/cnv/0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 380) # mount -o loop /mnt/cnv/0 /data
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 381)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 382) The "seq" sub-directory grouping files for sequential write zones has in this
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 383) example 55356 zones::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 384)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 385) # ls -lv /mnt/seq
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 386) total 14511243264
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 387) -rw-r----- 1 root root 0 Nov 25 13:23 0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 388) -rw-r----- 1 root root 0 Nov 25 13:23 1
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 389) -rw-r----- 1 root root 0 Nov 25 13:23 2
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 390) ...
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 391) -rw-r----- 1 root root 0 Nov 25 13:23 55354
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 392) -rw-r----- 1 root root 0 Nov 25 13:23 55355
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 393)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 394) For sequential write zone files, the file size changes as data is appended at
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 395) the end of the file, similarly to any regular file system::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 396)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 397) # dd if=/dev/zero of=/mnt/seq/0 bs=4096 count=1 conv=notrunc oflag=direct
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 398) 1+0 records in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 399) 1+0 records out
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 400) 4096 bytes (4.1 kB, 4.0 KiB) copied, 0.00044121 s, 9.3 MB/s
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 401)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 402) # ls -l /mnt/seq/0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 403) -rw-r----- 1 root root 4096 Nov 25 13:23 /mnt/seq/0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 404)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 405) The written file can be truncated to the zone size, preventing any further
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 406) write operation::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 407)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 408) # truncate -s 268435456 /mnt/seq/0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 409) # ls -l /mnt/seq/0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 410) -rw-r----- 1 root root 268435456 Nov 25 13:49 /mnt/seq/0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 411)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 412) Truncation to 0 size allows freeing the file zone storage space and restart
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 413) append-writes to the file::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 414)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 415) # truncate -s 0 /mnt/seq/0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 416) # ls -l /mnt/seq/0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 417) -rw-r----- 1 root root 0 Nov 25 13:49 /mnt/seq/0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 418)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 419) Since files are statically mapped to zones on the disk, the number of blocks
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 420) of a file as reported by stat() and fstat() indicates the capacity of the file
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 421) zone::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 422)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 423) # stat /mnt/seq/0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 424) File: /mnt/seq/0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 425) Size: 0 Blocks: 524288 IO Block: 4096 regular empty file
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 426) Device: 870h/2160d Inode: 50431 Links: 1
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 427) Access: (0640/-rw-r-----) Uid: ( 0/ root) Gid: ( 0/ root)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 428) Access: 2019-11-25 13:23:57.048971997 +0900
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 429) Modify: 2019-11-25 13:52:25.553805765 +0900
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 430) Change: 2019-11-25 13:52:25.553805765 +0900
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 431) Birth: -
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 432)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 433) The number of blocks of the file ("Blocks") in units of 512B blocks gives the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 434) maximum file size of 524288 * 512 B = 256 MB, corresponding to the device zone
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 435) capacity in this example. Of note is that the "IO block" field always
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 436) indicates the minimum I/O size for writes and corresponds to the device
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 437) physical sector size.
Orange Pi5 kernel
Deprecated Linux kernel 5.10.110 for OrangePi 5/5B/5+ boards
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