docs: filesystems: convert zonefs.txt to ReST

- Add a SPDX header;
- Add a document title;
- Some whitespace fixes and new line breaks;
- Mark literal blocks as such;
- Add it to filesystems/index.rst.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Acked-by: Damien Le Moal <damien.lemoal@wdc.com>
Link: https://lore.kernel.org/r/42a7cfcd19f6b904a9a3188fd4af71bed5050052.1581955849.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/filesystems/index.rst

@@ -95,3 +95,4 @@ Documentation for filesystem implementations.
    udf
    virtiofs
    vfat
+   zonefs

Documentation/filesystems/zonefs.rst

@@ -1,4 +1,8 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+================================================
 ZoneFS - Zone filesystem for Zoned block devices
+================================================
 
 Introduction
 ============
@@ -29,6 +33,7 @@ Zoned block devices
 Zoned storage devices belong to a class of storage devices with an address
 space that is divided into zones. A zone is a group of consecutive LBAs and all
 zones are contiguous (there are no LBA gaps). Zones may have different types.
+
 * Conventional zones: there are no access constraints to LBAs belonging to
   conventional zones. Any read or write access can be executed, similarly to a
   regular block device.
@@ -158,6 +163,7 @@ Format options
 --------------
 
 Several optional features of zonefs can be enabled at format time.
+
 * Conventional zone aggregation: ranges of contiguous conventional zones can be
   aggregated 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)
@@ -249,7 +255,7 @@ permissions.
 Further action taken by zonefs I/O error recovery can be controlled by the user
 with the "errors=xxx" mount option. The table below summarizes the result of
 zonefs I/O error processing depending on the mount option and on the zone
-conditions.
+conditions::
 
     +--------------+-----------+-----------------------------------------+
     |              |           |            Post error state             |
@@ -275,6 +281,7 @@ conditions.
     +--------------+-----------+-----------------------------------------+
 
 Further notes:
+
 * The "errors=remount-ro" mount option is the default behavior of zonefs I/O
   error processing if no errors mount option is specified.
 * With the "errors=remount-ro" mount option, the change of the file access
@@ -302,6 +309,7 @@ Mount options
 zonefs define the "errors=<behavior>" mount option to allow the user to specify
 zonefs behavior in response to I/O errors, inode size inconsistencies or zone
 condition chages. The defined behaviors are as follow:
+
 * remount-ro (default)
 * zone-ro
 * zone-offline
@@ -325,7 +333,7 @@ Examples
 --------
 
 The following formats a 15TB host-managed SMR HDD with 256 MB zones
-with the conventional zones aggregation feature enabled.
+with the conventional zones aggregation feature enabled::
 
     # mkzonefs -o aggr_cnv /dev/sdX
     # mount -t zonefs /dev/sdX /mnt
@@ -337,19 +345,19 @@ dr-xr-xr-x 2 root root 55356 Nov 25 13:23 seq
 The size of the zone files sub-directories indicate the number of files
 existing for each type of zones. In this example, there is only one
 conventional zone file (all conventional zones are aggregated under a single
-file).
+file)::
 
     # ls -l /mnt/cnv
     total 137101312
     -rw-r----- 1 root root 140391743488 Nov 25 13:23 0
 
-This aggregated conventional zone file can be used as a regular file.
+This aggregated conventional zone file can be used as a regular file::
 
     # mkfs.ext4 /mnt/cnv/0
     # mount -o loop /mnt/cnv/0 /data
 
 The "seq" sub-directory grouping files for sequential write zones has in this
-example 55356 zones.
+example 55356 zones::
 
     # ls -lv /mnt/seq
     total 14511243264
@@ -361,7 +369,7 @@ total 14511243264
     -rw-r----- 1 root root 0 Nov 25 13:23 55355
 
 For sequential write zone files, the file size changes as data is appended at
-the end of the file, similarly to any regular file system.
+the end of the file, similarly to any regular file system::
 
     # dd if=/dev/zero of=/mnt/seq/0 bs=4096 count=1 conv=notrunc oflag=direct
     1+0 records in
@@ -372,21 +380,21 @@ the end of the file, similarly to any regular file system.
     -rw-r----- 1 root root 4096 Nov 25 13:23 /mnt/seq/0
 
 The written file can be truncated to the zone size, preventing any further
-write operation.
+write operation::
 
     # truncate -s 268435456 /mnt/seq/0
     # ls -l /mnt/seq/0
     -rw-r----- 1 root root 268435456 Nov 25 13:49 /mnt/seq/0
 
 Truncation to 0 size allows freeing the file zone storage space and restart
-append-writes to the file.
+append-writes to the file::
 
     # truncate -s 0 /mnt/seq/0
     # ls -l /mnt/seq/0
     -rw-r----- 1 root root 0 Nov 25 13:49 /mnt/seq/0
 
 Since files are statically mapped to zones on the disk, the number of blocks of
-a file as reported by stat() and fstat() indicates the size of the file zone.
+a file as reported by stat() and fstat() indicates the size of the file zone::
 
     # stat /mnt/seq/0
     File: /mnt/seq/0