Merge tag 'docs-5.7' of git://git.lwn.net/linux

Pull documentation updates from Jonathan Corbet:
 "This has been a busy cycle for documentation work.

  Highlights include:

   - Lots of RST conversion work by Mauro, Daniel ALmeida, and others.
     Maybe someday we'll get to the end of this stuff...maybe...

   - Some organizational work to bring some order to the core-api
     manual.

   - Various new docs and additions to the existing documentation.

   - Typo fixes, warning fixes, ..."

* tag 'docs-5.7' of git://git.lwn.net/linux: (123 commits)
  Documentation: x86: exception-tables: document CONFIG_BUILDTIME_TABLE_SORT
  MAINTAINERS: adjust to filesystem doc ReST conversion
  docs: deprecated.rst: Add BUG()-family
  doc: zh_CN: add translation for virtiofs
  doc: zh_CN: index files in filesystems subdirectory
  docs: locking: Drop :c:func: throughout
  docs: locking: Add 'need' to hardirq section
  docs: conf.py: avoid thousands of duplicate label warning on Sphinx
  docs: prevent warnings due to autosectionlabel
  docs: fix reference to core-api/namespaces.rst
  docs: fix pointers to io-mapping.rst and io_ordering.rst files
  Documentation: Better document the softlockup_panic sysctl
  docs: hw-vuln: tsx_async_abort.rst: get rid of an unused ref
  docs: perf: imx-ddr.rst: get rid of a warning
  docs: filesystems: fuse.rst: supress a Sphinx warning
  docs: translations: it: avoid duplicate refs at programming-language.rst
  docs: driver.rst: supress two ReSt warnings
  docs: trace: events.rst: convert some new stuff to ReST format
  Documentation: Add io_ordering.rst to driver-api manual
  Documentation: Add io-mapping.rst to driver-api manual
  ...

1 files changed, 112 insertions, 0 deletions

diff --git a/Documentation/filesystems/omfs.rst b/Documentation/filesystems/omfs.rst
new file mode 100644
index 000000000000..4c8bb3074169
--- /dev/null
+++ b/Documentation/filesystems/omfs.rst
@@ -0,0 +1,112 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+================================
+Optimized MPEG Filesystem (OMFS)
+================================
+
+Overview
+========
+
+OMFS is a filesystem created by SonicBlue for use in the ReplayTV DVR
+and Rio Karma MP3 player.  The filesystem is extent-based, utilizing
+block sizes from 2k to 8k, with hash-based directories.  This
+filesystem driver may be used to read and write disks from these
+devices.
+
+Note, it is not recommended that this FS be used in place of a general
+filesystem for your own streaming media device.  Native Linux filesystems
+will likely perform better.
+
+More information is available at:
+
+    http://linux-karma.sf.net/
+
+Various utilities, including mkomfs and omfsck, are included with
+omfsprogs, available at:
+
+    http://bobcopeland.com/karma/
+
+Instructions are included in its README.
+
+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
+    ============   ========================================
+
+Disk format
+===========
+
+OMFS discriminates between "sysblocks" and normal data blocks.  The sysblock
+group consists of super block information, file metadata, directory structures,
+and extents.  Each sysblock has a header containing CRCs of the entire
+sysblock, and may be mirrored in successive blocks on the disk.  A sysblock may
+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::
+
+    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 */
+	    char h_fill1[2];
+	    u8 h_version;                   /* version, always 1 */
+	    char h_type;                    /* OMFS_INODE_X */
+	    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::
+
+    struct omfs_inode {
+	    struct omfs_header i_head;      /* header */
+	    __be64 i_parent;                /* parent containing this inode */
+	    __be64 i_sibling;               /* next inode in hash bucket */
+	    __be64 i_ctime;                 /* ctime, in milliseconds */
+	    char i_fill1[35];
+	    char i_type;                    /* OMFS_[DIR,FILE] */
+	    __be32 i_fill2;
+	    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.
+Lookup requires hashing the filename, then seeking across i_sibling pointers
+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::
+
+    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 {
+	    __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
+being ~0 and e_blocks being ones'-complement of the total number of blocks
+in the table.
+
+If this table overflows, a continuation inode is written and pointed to by
+e_next.  These have a header but lack the rest of the inode structure.
+