docs: block: convert to ReST

Rename the block documentation files to ReST, add an
index for them and adjust in order to produce a nice html
output via the Sphinx build system.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

1 files changed, 126 insertions, 0 deletions

diff --git a/Documentation/block/null_blk.rst b/Documentation/block/null_blk.rst
new file mode 100644
index 000000000000..31451d80783c
--- /dev/null
+++ b/Documentation/block/null_blk.rst
@@ -0,0 +1,126 @@
+========================
+Null block device driver
+========================
+
+1. Overview
+===========
+
+The null block device (/dev/nullb*) is used for benchmarking the various
+block-layer implementations. It emulates a block device of X gigabytes in size.
+The following instances are possible:
+
+  Single-queue block-layer
+
+    - Request-based.
+    - Single submission queue per device.
+    - Implements IO scheduling algorithms (CFQ, Deadline, noop).
+
+  Multi-queue block-layer
+
+    - Request-based.
+    - Configurable submission queues per device.
+
+  No block-layer (Known as bio-based)
+
+    - Bio-based. IO requests are submitted directly to the device driver.
+    - Directly accepts bio data structure and returns them.
+
+All of them have a completion queue for each core in the system.
+
+2. Module parameters applicable for all instances
+=================================================
+
+queue_mode=[0-2]: Default: 2-Multi-queue
+  Selects which block-layer the module should instantiate with.
+
+  =  ============
+  0  Bio-based
+  1  Single-queue
+  2  Multi-queue
+  =  ============
+
+home_node=[0--nr_nodes]: Default: NUMA_NO_NODE
+  Selects what CPU node the data structures are allocated from.
+
+gb=[Size in GB]: Default: 250GB
+  The size of the device reported to the system.
+
+bs=[Block size (in bytes)]: Default: 512 bytes
+  The block size reported to the system.
+
+nr_devices=[Number of devices]: Default: 1
+  Number of block devices instantiated. They are instantiated as /dev/nullb0,
+  etc.
+
+irqmode=[0-2]: Default: 1-Soft-irq
+  The completion mode used for completing IOs to the block-layer.
+
+  =  ===========================================================================
+  0  None.
+  1  Soft-irq. Uses IPI to complete IOs across CPU nodes. Simulates the overhead
+     when IOs are issued from another CPU node than the home the device is
+     connected to.
+  2  Timer: Waits a specific period (completion_nsec) for each IO before
+     completion.
+  =  ===========================================================================
+
+completion_nsec=[ns]: Default: 10,000ns
+  Combined with irqmode=2 (timer). The time each completion event must wait.
+
+submit_queues=[1..nr_cpus]:
+  The number of submission queues attached to the device driver. If unset, it
+  defaults to 1. For multi-queue, it is ignored when use_per_node_hctx module
+  parameter is 1.
+
+hw_queue_depth=[0..qdepth]: Default: 64
+  The hardware queue depth of the device.
+
+III: Multi-queue specific parameters
+
+use_per_node_hctx=[0/1]: Default: 0
+
+  =  =====================================================================
+  0  The number of submit queues are set to the value of the submit_queues
+     parameter.
+  1  The multi-queue block layer is instantiated with a hardware dispatch
+     queue for each CPU node in the system.
+  =  =====================================================================
+
+no_sched=[0/1]: Default: 0
+
+  =  ======================================
+  0  nullb* use default blk-mq io scheduler
+  1  nullb* doesn't use io scheduler
+  =  ======================================
+
+blocking=[0/1]: Default: 0
+
+  =  ===============================================================
+  0  Register as a non-blocking blk-mq driver device.
+  1  Register as a blocking blk-mq driver device, null_blk will set
+     the BLK_MQ_F_BLOCKING flag, indicating that it sometimes/always
+     needs to block in its ->queue_rq() function.
+  =  ===============================================================
+
+shared_tags=[0/1]: Default: 0
+
+  =  ================================================================
+  0  Tag set is not shared.
+  1  Tag set shared between devices for blk-mq. Only makes sense with
+     nr_devices > 1, otherwise there's no tag set to share.
+  =  ================================================================
+
+zoned=[0/1]: Default: 0
+
+  =  ======================================================================
+  0  Block device is exposed as a random-access block device.
+  1  Block device is exposed as a host-managed zoned block device. Requires
+     CONFIG_BLK_DEV_ZONED.
+  =  ======================================================================
+
+zone_size=[MB]: Default: 256
+  Per zone size when exposed as a zoned block device. Must be a power of two.
+
+zone_nr_conv=[nr_conv]: Default: 0
+  The number of conventional zones to create when block device is zoned.  If
+  zone_nr_conv >= nr_zones, it will be reduced to nr_zones - 1.