docs: filesystems: convert omfs.txt to ReST

- Add a SPDX header;
- Adjust document title;
- Mark literal blocks as such;
- Add table markups;
- Add it to filesystems/index.rst.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Acked-by: Bob Copeland <me@bobcopeland.com>
Link: https://lore.kernel.org/r/0c125c7c971d81a557ca954992b8d770a9d1e3e8.1581955849.git.mchehab+huawei@kernel.orgSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/filesystems/index.rst

@@ -78,6 +78,7 @@ Documentation for filesystem implementations.
    ntfs
    ocfs2
    ocfs2-online-filecheck
+   omfs
    overlayfs
    virtiofs
    vfat

Documentation/filesystems/omfs.txt → Documentation/filesystems/omfs.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+================================
 Optimized MPEG Filesystem (OMFS)
+================================
 
 Overview
 ========
@@ -29,11 +33,13 @@ Options
 
 OMFS supports the following mount-time options:
 
-    uid=n        - make all files owned by specified user
-    gid=n        - make all files owned by specified group
-    umask=xxx    - set permission umask to xxx
-    fmask=xxx    - set umask to xxx for files
-    dmask=xxx    - set umask to xxx for directories
+    ============   ========================================
+    uid=n          make all files owned by specified user
+    gid=n          make all files owned by specified group
+    umask=xxx      set permission umask to xxx
+    fmask=xxx      set umask to xxx for files
+    dmask=xxx      set umask to xxx for directories
+    ============   ========================================
 
 Disk format
 ===========
@@ -46,9 +52,9 @@ have a smaller size than a data block, but since they are both addressed by the
 same 64-bit block number, any remaining space in the smaller sysblock is
 unused.
 
-Sysblock header information:
+Sysblock header information::
 
-struct omfs_header {
+    struct omfs_header {
 	    __be64 h_self;                  /* FS block where this is located */
 	    __be32 h_body_size;             /* size of useful data after header */
 	    __be16 h_crc;                   /* crc-ccitt of body_size bytes */
@@ -58,11 +64,11 @@ struct omfs_header {
 	    u8 h_magic;                     /* OMFS_IMAGIC */
 	    u8 h_check_xor;                 /* XOR of header bytes before this */
 	    __be32 h_fill2;
-};
+    };
 
-Files and directories are both represented by omfs_inode:
+Files and directories are both represented by omfs_inode::
 
-struct omfs_inode {
+    struct omfs_inode {
 	    struct omfs_header i_head;      /* header */
 	    __be64 i_parent;                /* parent containing this inode */
 	    __be64 i_sibling;               /* next inode in hash bucket */
@@ -73,7 +79,7 @@ struct omfs_inode {
 	    char i_fill3[64];
 	    char i_name[OMFS_NAMELEN];      /* filename */
 	    __be64 i_size;                  /* size of file, in bytes */
-};
+    };
 
 Directories in OMFS are implemented as a large hash table.  Filenames are
 hashed then prepended into the bucket list beginning at OMFS_DIR_START.
@@ -82,19 +88,19 @@ until a match is found on i_name.  Empty buckets are represented by block
 pointers with all-1s (~0).
 
 A file is an omfs_inode structure followed by an extent table beginning at
-OMFS_EXTENT_START:
+OMFS_EXTENT_START::
 
-struct omfs_extent_entry {
+    struct omfs_extent_entry {
 	    __be64 e_cluster;               /* start location of a set of blocks */
 	    __be64 e_blocks;                /* number of blocks after e_cluster */
-};
+    };
 
-struct omfs_extent {
+    struct omfs_extent {
 	    __be64 e_next;                  /* next extent table location */
 	    __be32 e_extent_count;          /* total # extents in this table */
 	    __be32 e_fill;
 	    struct omfs_extent_entry e_entry;       /* start of extent entries */
-};
+    };
 
 Each extent holds the block offset followed by number of blocks allocated to
 the extent.  The final extent in each table is a terminator with e_cluster