Initial WIP new user's manual

Makefile

@@ -114,6 +114,9 @@ endif
 # Rebuild the 'version' command any time the version string changes
 cmd_version.o : .version
 
+doc/bcachefs.5: doc/bcachefs.5.txt
+	a2x -f manpage doc/bcachefs.5.txt
+
 .PHONY: install
 install: INITRAMFS_HOOK=$(INITRAMFS_DIR)/hooks/bcachefs
 install: INITRAMFS_SCRIPT=$(INITRAMFS_DIR)/scripts/local-premount/bcachefs

doc/bcachefs.5.txt

@@ -0,0 +1,110 @@
+BCACHEFS(5)
+===========
+
+NAME
+----
+bcachefs - bcachefs overview, user's manual and configuration
+
+DESCRIPTION
+-----------
+Bcachefs is a multi device copy on write filesystem that supports
+
+ Checksumming
+ Compression
+ Encryption
+ Reflink
+ Caching
+ Replication
+ Erasure coding (reed-solomon)
+
+And more. This document is intended to be an overview of the various features
+and use cases.
+
+Configuration
+-------------
+Most configuration is done via filesystem options that can be set at format
+time, mount time (as mount -o parameters), or changed at runtime via sysfs (via
+the /sys/fs/bcachefs/<UUID>/options/ directory).
+
+Many of those options (particularly those that control the IO path) can also be
+set on individual files and directories, via the bcachefs setattr command (which
+internally mostly works via the extended attribute interface, but the setattr
+command takes care to propagate options to children correctly).
+
+ * TODO: include master list of options from opts.h
+#include "opts.mdwn"
+
+Device management
+-----------------
+Devices can be added, removed, and resized at will, at runtime. There is no
+fixed topology or data layout, as with hardware RAID or ZFS, and devices need
+not be the same size - the allocator will stripe across multiple disks,
+preferring to allocate from disks with more free space so that disks all fill up
+at the same time.
+
+We generally avoid per-device options, preferring instead options that can be
+overridden on files or directories, but there are some:
+
+ *durability* 
+
+Device labels, targets
+----------------------
+
+Configuration options that point to targets (i.e. a disk or group of disks) may
+be passed either a device (i.e. /dev/sda), or a label. Labels are assigned to
+disks (and need not be unique), and these labels form a nested heirarchy: this
+allows disks to be grouped together and referred to either individually or as a
+group.
+
+For example, given disks formatted with these labels:
+
+  bcachefs format -g controller1.hdd.hdd1 /dev/sda	\
+                  -g controller1.hdd.hdd2 /dev/sdb	\
+                  -g controller1.ssd.ssd1 /dev/sdc	\
+                  -g controller1.ssd.ssd1 /dev/sdd	\
+                  -g controller2.hdd1     /dev/sde	\
+                  -g controller2.hdd2     /dev/sdf
+
+Configuration options such as foreground_target may then refer to controller1,
+or controller1.hdd, or controller1.hdd1 - or to /dev/sda directly.
+
+Data placement, caching
+-----------------------
+
+The following options control which disks data is written to:
+
+ * foreground_target
+ * background_target
+ * promote_target
+
+The foreground_target option is used to direct writes from applications. The
+background_target option, if set, will cause data to be moved to that target in
+the background by the rebalance thread some time after it has been initially
+written - leaving behind the original copy, but marking it cached so that it can
+be discarded by the allocator. The promote_target will will cause reads to write
+a cached copy of the data being read to that target, if it doesn't exist.
+
+Together, these options can be used for writeback caching, like so:
+
+  foregroud_target=ssd
+  background_target=hdd
+  promote_target=ssd
+
+Writethrough caching requires telling bcachefs not to trust the cache device,
+which does require a per-device option and thus can't completely be done with
+per-file options. This is done by setting the device's durability to 0.
+
+These options can all be set on individual files or directories. They can also
+be used to pin a specific file or directory to a specific device or target:
+
+  foreground_target=ssd
+  background_target=
+  promote_target=
+
+Note that if the target specified is full, the write will spill over to the rest
+of the filesystem.
+
+Data protection
+---------------
+
+foo