Re: [PATCH 2/2] zonefs: Add documentation

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 12/12/19 7:38 PM, Damien Le Moal wrote:
Add the new file Documentation/filesystems/zonefs.txt to document zonefs
principles and user-space tool usage.

Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxx>
---
  Documentation/filesystems/zonefs.txt | 150 +++++++++++++++++++++++++++
  MAINTAINERS                          |   1 +
  2 files changed, 151 insertions(+)
  create mode 100644 Documentation/filesystems/zonefs.txt

diff --git a/Documentation/filesystems/zonefs.txt b/Documentation/filesystems/zonefs.txt
new file mode 100644
index 000000000000..e5d798f4087d
--- /dev/null
+++ b/Documentation/filesystems/zonefs.txt
@@ -0,0 +1,150 @@
+ZoneFS - Zone filesystem for Zoned block devices
+
+Overview
+========
+
+zonefs is a very simple file system exposing each zone of a zoned block device
+as a file. Unlike a regular file system with zoned block device support (e.g.
+f2fs), zonefs does not hide the sequential write constraint of zoned block
+devices to the user. Files representing sequential write zones of the device
+must be written sequentially starting from the end of the file (append only
+writes).
+
+As such, zonefs is in essence closer to a raw block device access interface
+than to a full featured POSIX file system. The goal of zonefs is to simplify
+the implementation of zoned block devices support in applications by replacing
+raw block device file accesses with a richer file API, avoiding relying on
+direct block device file ioctls which may be more obscure to developers. One
+example of this approach is the implementation of LSM (log-structured merge)
+tree structures (such as used in RocksDB and LevelDB) on zoned block devices by
+allowing SSTables to be stored in a zone file similarly to a regular file system
+rather than as a range of sectors of the entire disk. The introduction of the
+higher level construct "one file is one zone" can help reducing the amount of
+changes needed in the application as well as introducing support for different
+application programming languages.
+
+zonefs on-disk metadata is reduced to a super block which persistently stores a
+magic number and optional features flags and values. On mount, zonefs uses
+blkdev_report_zones() to obtain the device zone configuration and populates
+the mount point with a static file tree solely based on this information.
+E.g. file sizes come from the device zone type and write pointer offset managed
+by the device itself.
+
+The zone files created on mount have the following characteristics.
+1) Files representing zones of the same type are grouped together
+   under the same sub-directory:
+  * For conventional zones, the sub-directory "cnv" is used.
+  * For sequential write zones, the sub-directory "seq" is used.
+  These two directories are the only directories that exist in zonefs. Users
+  cannot create other directories and cannot rename nor delete the "cnv" and
+  "seq" sub-directories.
+2) The name of zone files is the number of the file within the zone type
+   sub-directory, in order of increasing zone start sector.
+3) The size of conventional zone files is fixed to the device zone size.
+   Conventional zone files cannot be truncated.
+4) The size of sequential zone files represent the file's zone write pointer
+   position relative to the zone start sector. Truncating these files is
+   allowed only down to 0, in wich case, the zone is reset to rewind the file
+   zone write pointer position to the start of the zone, or up to the zone size,
+   in which case the file's zone is transitioned to the FULL state (finish zone
+   operation).
+5) All read and write operations to files are not allowed beyond the file zone
+   size. Any access exceeding the zone size is failed with the -EFBIG error.
+6) Creating, deleting, renaming or modifying any attribute of files and
+   sub-directories is not allowed.
+
+Several optional features of zonefs can be enabled at format time.
+* Conventional zone aggregation: ranges of contiguous conventional zones can be
+  agregated into a single larger file instead of the default one file per zone.
+* File ownership: The owner UID and GID of zone files is by default 0 (root)
+  but can be changed to any valid UID/GID.
+* File access permissions: the default 640 access permissions can be changed.
+

Please mention the 'direct writes only to sequential zones' restriction.

Cheers,

Hannes
--
Dr. Hannes Reinecke            Teamlead Storage & Networking
hare@xxxxxxx                               +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer



[Index of Archives]     [XFS Filesystem Development (older mail)]     [Linux Filesystem Development]     [Linux Audio Users]     [Yosemite Trails]     [Linux Kernel]     [Linux RAID]     [Linux SCSI]


  Powered by Linux