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Message-ID: <153124301692.17949.4053530771699546735.stgit@magnolia>
Date: Tue, 10 Jul 2018 10:16:56 -0700
From: "Darrick J. Wong" <darrick.wong@...cle.com>
To: tytso@....edu, darrick.wong@...cle.com
Cc: linux-ext4@...r.kernel.org
Subject: [PATCH 02/13] ext4: convert ext4.rst to restructuredtext format
From: Darrick J. Wong <darrick.wong@...cle.com>
Convert the existing ext4 documentation into rst format and link it in
with the rest of the kernel documentation.
Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
---
Documentation/filesystems/ext4/ext4.rst | 113 +++++++++++++++++-------------
Documentation/filesystems/ext4/index.rst | 16 ++++
Documentation/filesystems/index.rst | 8 ++
3 files changed, 89 insertions(+), 48 deletions(-)
create mode 100644 Documentation/filesystems/ext4/index.rst
diff --git a/Documentation/filesystems/ext4/ext4.rst b/Documentation/filesystems/ext4/ext4.rst
index 7f628b9f7c4b..f468e91bf2ea 100644
--- a/Documentation/filesystems/ext4/ext4.rst
+++ b/Documentation/filesystems/ext4/ext4.rst
@@ -1,6 +1,8 @@
+.. SPDX-License-Identifier: GPL-2.0
-Ext4 Filesystem
-===============
+========================
+General Information
+========================
Ext4 is an advanced level of the ext3 filesystem which incorporates
scalability and reliability enhancements for supporting large filesystems
@@ -11,18 +13,18 @@ Mailing list: linux-ext4@...r.kernel.org
Web site: http://ext4.wiki.kernel.org
-1. Quick usage instructions:
-===========================
+Quick usage instructions
+========================
Note: More extensive information for getting started with ext4 can be
- found at the ext4 wiki site at the URL:
- http://ext4.wiki.kernel.org/index.php/Ext4_Howto
+found at the ext4 wiki site at the URL:
+http://ext4.wiki.kernel.org/index.php/Ext4_Howto
- Compile and install the latest version of e2fsprogs (as of this
writing version 1.41.3) from:
http://sourceforge.net/project/showfiles.php?group_id=2406
-
+
or
https://www.kernel.org/pub/linux/kernel/people/tytso/e2fsprogs/
@@ -37,16 +39,16 @@ Note: More extensive information for getting started with ext4 can be
you will need to merge your changes with the version from e2fsprogs
1.41.x.
- - Create a new filesystem using the ext4 filesystem type:
+ - Create a new filesystem using the ext4 filesystem type:::
- # mke2fs -t ext4 /dev/hda1
+ # mke2fs -t ext4 /dev/hda1
- Or to configure an existing ext3 filesystem to support extents:
+ Or to configure an existing ext3 filesystem to support extents:::
# tune2fs -O extents /dev/hda1
If the filesystem was created with 128 byte inodes, it can be
- converted to use 256 byte for greater efficiency via:
+ converted to use 256 byte for greater efficiency via:::
# tune2fs -I 256 /dev/hda1
@@ -54,7 +56,7 @@ Note: More extensive information for getting started with ext4 can be
filesystem back to ext3; so please do not do try this on production
filesystems.)
- - Mounting:
+ - Mounting:::
# mount -t ext4 /dev/hda1 /wherever
@@ -75,10 +77,11 @@ Note: More extensive information for getting started with ext4 can be
the filesystem with a large journal can also be helpful for
metadata-intensive workloads.
-2. Features
-===========
+Features
+========
-2.1 Currently available
+Currently Available
+-------------------
* ability to use filesystems > 16TB (e2fsprogs support not available yet)
* extent format reduces metadata overhead (RAM, IO for access, transactions)
@@ -103,7 +106,8 @@ Note: More extensive information for getting started with ext4 can be
[1] Filesystems with a block size of 1k may see a limit imposed by the
directory hash tree having a maximum depth of two.
-2.2 Candidate features for future inclusion
+Candidate Features for Future Inclusion
+---------------------------------------
* online defrag (patches available but not well tested)
* reduced mke2fs time via lazy itable initialization in conjunction with
@@ -122,12 +126,15 @@ grouping of bitmaps and inode tables. Some test results available here:
- http://www.bullopensource.org/ext4/20080818-ffsb/ffsb-write-2.6.27-rc1.html
- http://www.bullopensource.org/ext4/20080818-ffsb/ffsb-readwrite-2.6.27-rc1.html
-3. Options
-==========
+Options
+=======
When mounting an ext4 filesystem, the following option are accepted:
(*) == default
+======================= ===========
+Mount Option Description
+======================= ===========
ro Mount filesystem read only. Note that ext4 will
replay the journal (and thus write to the
partition) even when mounted "read only". The
@@ -387,33 +394,38 @@ i_version Enable 64-bit inode version support. This option is
dax Use direct access (no page cache). See
Documentation/filesystems/dax.txt. Note that
this option is incompatible with data=journal.
+======================= ===========
Data Mode
=========
There are 3 different data modes:
* writeback mode
-In data=writeback mode, ext4 does not journal data at all. This mode provides
-a similar level of journaling as that of XFS, JFS, and ReiserFS in its default
-mode - metadata journaling. A crash+recovery can cause incorrect data to
-appear in files which were written shortly before the crash. This mode will
-typically provide the best ext4 performance.
+
+ In data=writeback mode, ext4 does not journal data at all. This mode provides
+ a similar level of journaling as that of XFS, JFS, and ReiserFS in its default
+ mode - metadata journaling. A crash+recovery can cause incorrect data to
+ appear in files which were written shortly before the crash. This mode will
+ typically provide the best ext4 performance.
* ordered mode
-In data=ordered mode, ext4 only officially journals metadata, but it logically
-groups metadata information related to data changes with the data blocks into a
-single unit called a transaction. When it's time to write the new metadata
-out to disk, the associated data blocks are written first. In general,
-this mode performs slightly slower than writeback but significantly faster than journal mode.
+
+ In data=ordered mode, ext4 only officially journals metadata, but it logically
+ groups metadata information related to data changes with the data blocks into
+ a single unit called a transaction. When it's time to write the new metadata
+ out to disk, the associated data blocks are written first. In general, this
+ mode performs slightly slower than writeback but significantly faster than
+ journal mode.
* journal mode
-data=journal mode provides full data and metadata journaling. All new data is
-written to the journal first, and then to its final location.
-In the event of a crash, the journal can be replayed, bringing both data and
-metadata into a consistent state. This mode is the slowest except when data
-needs to be read from and written to disk at the same time where it
-outperforms all others modes. Enabling this mode will disable delayed
-allocation and O_DIRECT support.
+
+ data=journal mode provides full data and metadata journaling. All new data is
+ written to the journal first, and then to its final location. In the event of
+ a crash, the journal can be replayed, bringing both data and metadata into a
+ consistent state. This mode is the slowest except when data needs to be read
+ from and written to disk at the same time where it outperforms all others
+ modes. Enabling this mode will disable delayed allocation and O_DIRECT
+ support.
/proc entries
=============
@@ -425,10 +437,12 @@ Information about mounted ext4 file systems can be found in
in table below.
Files in /proc/fs/ext4/<devname>
-..............................................................................
+
+================ =======
File Content
+================ =======
mb_groups details of multiblock allocator buddy cache of free blocks
-..............................................................................
+================ =======
/sys entries
============
@@ -439,28 +453,30 @@ Information about mounted ext4 file systems can be found in
/sys/fs/ext4/dm-0). The files in each per-device directory are shown
in table below.
-Files in /sys/fs/ext4/<devname>
+Files in /sys/fs/ext4/<devname>:
+
(see also Documentation/ABI/testing/sysfs-fs-ext4)
-..............................................................................
- File Content
+============================= =======
+File Content
+============================= =======
delayed_allocation_blocks This file is read-only and shows the number of
blocks that are dirty in the page cache, but
which do not have their location in the
filesystem allocated yet.
- inode_goal Tuning parameter which (if non-zero) controls
+inode_goal Tuning parameter which (if non-zero) controls
the goal inode used by the inode allocator in
preference to all other allocation heuristics.
This is intended for debugging use only, and
should be 0 on production systems.
- inode_readahead_blks Tuning parameter which controls the maximum
+inode_readahead_blks Tuning parameter which controls the maximum
number of inode table blocks that ext4's inode
table readahead algorithm will pre-read into
the buffer cache
- lifetime_write_kbytes This file is read-only and shows the number of
+lifetime_write_kbytes This file is read-only and shows the number of
kilobytes of data that have been written to this
filesystem since it was created.
@@ -508,7 +524,7 @@ Files in /sys/fs/ext4/<devname>
in the file system. If there is not enough space
for the reserved space when mounting the file
mount will _not_ fail.
-..............................................................................
+============================= =======
Ioctls
======
@@ -518,8 +534,10 @@ through the system call interfaces. The list of all Ext4 specific ioctls are
shown in the table below.
Table of Ext4 specific ioctls
-..............................................................................
- Ioctl Description
+
+============================= ===========
+Ioctl Description
+============================= ===========
EXT4_IOC_GETFLAGS Get additional attributes associated with inode.
The ioctl argument is an integer bitfield, with
bit values described in ext4.h. This ioctl is an
@@ -610,8 +628,7 @@ Table of Ext4 specific ioctls
normal user by accident.
The data blocks of the previous boot loader
will be associated with the given inode.
-
-..............................................................................
+============================= ===========
References
==========
diff --git a/Documentation/filesystems/ext4/index.rst b/Documentation/filesystems/ext4/index.rst
new file mode 100644
index 000000000000..1270b34f643f
--- /dev/null
+++ b/Documentation/filesystems/ext4/index.rst
@@ -0,0 +1,16 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+====
+ext4
+====
+
+General usage and on-disk artifacts writen by ext4. More documentation may
+be ported from the wiki as time permits. This should be considered the
+canonical source of information as the details here have been reviewed by
+the ext4 community.
+
+.. toctree::
+ :maxdepth: 5
+ :numbered:
+
+ ext4
diff --git a/Documentation/filesystems/index.rst b/Documentation/filesystems/index.rst
index 53b89d0edc15..7c57b3927308 100644
--- a/Documentation/filesystems/index.rst
+++ b/Documentation/filesystems/index.rst
@@ -2,6 +2,14 @@
Linux Filesystems API
=====================
+The documentation in this section are provided by specific filesystem
+subprojects.
+
+.. toctree::
+ :maxdepth: 2
+
+ ext4/index
+
The Linux VFS
=============
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