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docs: make ext4 readme tables readable 

The tables in the ext4 readme are not particularly space efficient in
the text or html outputs, and they're totally broken in the pdf output.
Convert them into titled paragraphs so that they render more nicely.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Darrick J. Wong 2018-10-02 22:45:25 -04:00 committed by Theodore Ts'o
parent de7abd7bbb
commit c0e3e0406a
1 changed files with 330 additions and 369 deletions
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Documentation/filesystems/ext4/ext4.rst
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@ -101,269 +101,256 @@ Options
When mounting an ext4 filesystem, the following option are accepted: When mounting an ext4 filesystem, the following option are accepted:
(*) == default (*) == default
======================= ======================================================= ro
Mount Option Description Mount filesystem read only. Note that ext4 will replay the journal (and
======================= ======================================================= thus write to the partition) even when mounted "read only". The mount
ro Mount filesystem read only. Note that ext4 will options "ro,noload" can be used to prevent writes to the filesystem.
replay the journal (and thus write to the
partition) even when mounted "read only". The
mount options "ro,noload" can be used to prevent
writes to the filesystem.
journal_checksum Enable checksumming of the journal transactions. journal_checksum
This will allow the recovery code in e2fsck and the Enable checksumming of the journal transactions. This will allow the
kernel to detect corruption in the kernel. It is a recovery code in e2fsck and the kernel to detect corruption in the
compatible change and will be ignored by older kernels. kernel. It is a compatible change and will be ignored by older
kernels.
journal_async_commit Commit block can be written to disk without waiting journal_async_commit
for descriptor blocks. If enabled older kernels cannot Commit block can be written to disk without waiting for descriptor
mount the device. This will enable 'journal_checksum' blocks. If enabled older kernels cannot mount the device. This will
internally. enable 'journal_checksum' internally.
journal_path=path journal_path=path, journal_dev=devnum
journal_dev=devnum When the external journal device's major/minor numbers When the external journal device's major/minor numbers have changed,
have changed, these options allow the user to specify these options allow the user to specify the new journal location. The
the new journal location. The journal device is journal device is identified through either its new major/minor numbers
identified through either its new major/minor numbers encoded in devnum, or via a path to the device.
encoded in devnum, or via a path to the device.
norecovery Don't load the journal on mounting. Note that norecovery, noload
noload if the filesystem was not unmounted cleanly, Don't load the journal on mounting. Note that if the filesystem was
skipping the journal replay will lead to the not unmounted cleanly, skipping the journal replay will lead to the
filesystem containing inconsistencies that can filesystem containing inconsistencies that can lead to any number of
lead to any number of problems. problems.
data=journal All data are committed into the journal prior to being data=journal
written into the main file system. Enabling All data are committed into the journal prior to being written into the
this mode will disable delayed allocation and main file system. Enabling this mode will disable delayed allocation
O_DIRECT support. and O_DIRECT support.
data=ordered (*) All data are forced directly out to the main file data=ordered (*)
system prior to its metadata being committed to the All data are forced directly out to the main file system prior to its
journal. metadata being committed to the journal.
data=writeback Data ordering is not preserved, data may be written data=writeback
into the main file system after its metadata has been Data ordering is not preserved, data may be written into the main file
committed to the journal. system after its metadata has been committed to the journal.
commit=nrsec (*) Ext4 can be told to sync all its data and metadata commit=nrsec (*)
every 'nrsec' seconds. The default value is 5 seconds. Ext4 can be told to sync all its data and metadata every 'nrsec'
This means that if you lose your power, you will lose seconds. The default value is 5 seconds. This means that if you lose
as much as the latest 5 seconds of work (your your power, you will lose as much as the latest 5 seconds of work (your
filesystem will not be damaged though, thanks to the filesystem will not be damaged though, thanks to the journaling). This
journaling). This default value (or any low value) default value (or any low value) will hurt performance, but it's good
will hurt performance, but it's good for data-safety. for data-safety. Setting it to 0 will have the same effect as leaving
Setting it to 0 will have the same effect as leaving it at the default (5 seconds). Setting it to very large values will
it at the default (5 seconds). improve performance.
Setting it to very large values will improve
performance.
barrier=<0|1(*)> This enables/disables the use of write barriers in barrier=<0|1(*)>, barrier(*), nobarrier
barrier(*) the jbd code. barrier=0 disables, barrier=1 enables. This enables/disables the use of write barriers in the jbd code.
nobarrier This also requires an IO stack which can support barrier=0 disables, barrier=1 enables. This also requires an IO stack
barriers, and if jbd gets an error on a barrier which can support barriers, and if jbd gets an error on a barrier
write, it will disable again with a warning. write, it will disable again with a warning. Write barriers enforce
Write barriers enforce proper on-disk ordering proper on-disk ordering of journal commits, making volatile disk write
of journal commits, making volatile disk write caches caches safe to use, at some performance penalty. If your disks are
safe to use, at some performance penalty. If battery-backed in one way or another, disabling barriers may safely
your disks are battery-backed in one way or another, improve performance. The mount options "barrier" and "nobarrier" can
disabling barriers may safely improve performance. also be used to enable or disable barriers, for consistency with other
The mount options "barrier" and "nobarrier" can ext4 mount options.
also be used to enable or disable barriers, for
consistency with other ext4 mount options.
inode_readahead_blks=n This tuning parameter controls the maximum inode_readahead_blks=n
number of inode table blocks that ext4's inode This tuning parameter controls the maximum number of inode table blocks
table readahead algorithm will pre-read into that ext4's inode table readahead algorithm will pre-read into the
the buffer cache. The default value is 32 blocks. buffer cache. The default value is 32 blocks.
nouser_xattr Disables Extended User Attributes. See the nouser_xattr
attr(5) manual page for more information about Disables Extended User Attributes. See the attr(5) manual page for
extended attributes. more information about extended attributes.
noacl This option disables POSIX Access Control List noacl
support. If ACL support is enabled in the kernel This option disables POSIX Access Control List support. If ACL support
configuration (CONFIG_EXT4_FS_POSIX_ACL), ACL is is enabled in the kernel configuration (CONFIG_EXT4_FS_POSIX_ACL), ACL
enabled by default on mount. See the acl(5) manual is enabled by default on mount. See the acl(5) manual page for more
page for more information about acl. information about acl.
bsddf (*) Make 'df' act like BSD. bsddf (*)
minixdf Make 'df' act like Minix. Make 'df' act like BSD.
debug Extra debugging information is sent to syslog. minixdf
Make 'df' act like Minix.
abort Simulate the effects of calling ext4_abort() for debug
debugging purposes. This is normally used while Extra debugging information is sent to syslog.
remounting a filesystem which is already mounted.
errors=remount-ro Remount the filesystem read-only on an error. abort
errors=continue Keep going on a filesystem error. Simulate the effects of calling ext4_abort() for debugging purposes.
errors=panic Panic and halt the machine if an error occurs. This is normally used while remounting a filesystem which is already
(These mount options override the errors behavior mounted.
specified in the superblock, which can be configured
using tune2fs)
data_err=ignore(*) Just print an error message if an error occurs errors=remount-ro
in a file data buffer in ordered mode. Remount the filesystem read-only on an error.
data_err=abort Abort the journal if an error occurs in a file
data buffer in ordered mode.
grpid New objects have the group ID of their parent. errors=continue
bsdgroups Keep going on a filesystem error.
nogrpid (*) New objects have the group ID of their creator. errors=panic
sysvgroups Panic and halt the machine if an error occurs. (These mount options
override the errors behavior specified in the superblock, which can be
configured using tune2fs)
resgid=n The group ID which may use the reserved blocks. data_err=ignore(*)
Just print an error message if an error occurs in a file data buffer in
ordered mode.
data_err=abort
Abort the journal if an error occurs in a file data buffer in ordered
mode.
resuid=n The user ID which may use the reserved blocks. grpid | bsdgroups
New objects have the group ID of their parent.
sb=n Use alternate superblock at this location. nogrpid (*) | sysvgroups
New objects have the group ID of their creator.
quota These options are ignored by the filesystem. They resgid=n
noquota are used only by quota tools to recognize volumes The group ID which may use the reserved blocks.
grpquota where quota should be turned on. See documentation
usrquota in the quota-tools package for more details
(http://sourceforge.net/projects/linuxquota).
jqfmt=<quota type> These options tell filesystem details about quota resuid=n
usrjquota=<file> so that quota information can be properly updated The user ID which may use the reserved blocks.
grpjquota=<file> during journal replay. They replace the above
quota options. See documentation in the quota-tools
package for more details
(http://sourceforge.net/projects/linuxquota).
stripe=n Number of filesystem blocks that mballoc will try sb=
to use for allocation size and alignment. For RAID5/6 Use alternate superblock at this location.
systems this should be the number of data
disks * RAID chunk size in file system blocks.
delalloc (*) Defer block allocation until just before ext4 quota, noquota, grpquota, usrquota
writes out the block(s) in question. This These options are ignored by the filesystem. They are used only by
allows ext4 to better allocation decisions quota tools to recognize volumes where quota should be turned on. See
more efficiently. documentation in the quota-tools package for more details
nodelalloc Disable delayed allocation. Blocks are allocated (http://sourceforge.net/projects/linuxquota).
when the data is copied from userspace to the
page cache, either via the write(2) system call
or when an mmap'ed page which was previously
unallocated is written for the first time.
max_batch_time=usec Maximum amount of time ext4 should wait for jqfmt=<quota type>, usrjquota=<file>, grpjquota=<file>
additional filesystem operations to be batch These options tell filesystem details about quota so that quota
together with a synchronous write operation. information can be properly updated during journal replay. They replace
Since a synchronous write operation is going to the above quota options. See documentation in the quota-tools package
force a commit and then a wait for the I/O for more details (http://sourceforge.net/projects/linuxquota).
complete, it doesn't cost much, and can be a
huge throughput win, we wait for a small amount
of time to see if any other transactions can
piggyback on the synchronous write. The
algorithm used is designed to automatically tune
for the speed of the disk, by measuring the
amount of time (on average) that it takes to
finish committing a transaction. Call this time
the "commit time". If the time that the
transaction has been running is less than the
commit time, ext4 will try sleeping for the
commit time to see if other operations will join
the transaction. The commit time is capped by
the max_batch_time, which defaults to 15000us
(15ms). This optimization can be turned off
entirely by setting max_batch_time to 0.
min_batch_time=usec This parameter sets the commit time (as stripe=n
described above) to be at least min_batch_time. Number of filesystem blocks that mballoc will try to use for allocation
It defaults to zero microseconds. Increasing size and alignment. For RAID5/6 systems this should be the number of
this parameter may improve the throughput of data disks * RAID chunk size in file system blocks.
multi-threaded, synchronous workloads on very
fast disks, at the cost of increasing latency.
journal_ioprio=prio The I/O priority (from 0 to 7, where 0 is the delalloc (*)
highest priority) which should be used for I/O Defer block allocation until just before ext4 writes out the block(s)
operations submitted by kjournald2 during a in question. This allows ext4 to better allocation decisions more
commit operation. This defaults to 3, which is efficiently.
a slightly higher priority than the default I/O
priority.
auto_da_alloc(*) Many broken applications don't use fsync() when nodelalloc
noauto_da_alloc replacing existing files via patterns such as Disable delayed allocation. Blocks are allocated when the data is
fd = open("foo.new")/write(fd,..)/close(fd)/ copied from userspace to the page cache, either via the write(2) system
rename("foo.new", "foo"), or worse yet, call or when an mmap'ed page which was previously unallocated is
fd = open("foo", O_TRUNC)/write(fd,..)/close(fd). written for the first time.
If auto_da_alloc is enabled, ext4 will detect
the replace-via-rename and replace-via-truncate
patterns and force that any delayed allocation
blocks are allocated such that at the next
journal commit, in the default data=ordered
mode, the data blocks of the new file are forced
to disk before the rename() operation is
committed. This provides roughly the same level
of guarantees as ext3, and avoids the
"zero-length" problem that can happen when a
system crashes before the delayed allocation
blocks are forced to disk.
noinit_itable Do not initialize any uninitialized inode table max_batch_time=usec
blocks in the background. This feature may be Maximum amount of time ext4 should wait for additional filesystem
used by installation CD's so that the install operations to be batch together with a synchronous write operation.
process can complete as quickly as possible; the Since a synchronous write operation is going to force a commit and then
inode table initialization process would then be a wait for the I/O complete, it doesn't cost much, and can be a huge
deferred until the next time the file system throughput win, we wait for a small amount of time to see if any other
is unmounted. transactions can piggyback on the synchronous write. The algorithm
used is designed to automatically tune for the speed of the disk, by
measuring the amount of time (on average) that it takes to finish
committing a transaction. Call this time the "commit time". If the
time that the transaction has been running is less than the commit
time, ext4 will try sleeping for the commit time to see if other
operations will join the transaction. The commit time is capped by
the max_batch_time, which defaults to 15000us (15ms). This
optimization can be turned off entirely by setting max_batch_time to 0.
init_itable=n The lazy itable init code will wait n times the min_batch_time=usec
number of milliseconds it took to zero out the This parameter sets the commit time (as described above) to be at least
previous block group's inode table. This min_batch_time. It defaults to zero microseconds. Increasing this
minimizes the impact on the system performance parameter may improve the throughput of multi-threaded, synchronous
while file system's inode table is being initialized. workloads on very fast disks, at the cost of increasing latency.
discard Controls whether ext4 should issue discard/TRIM journal_ioprio=prio
nodiscard(*) commands to the underlying block device when The I/O priority (from 0 to 7, where 0 is the highest priority) which
blocks are freed. This is useful for SSD devices should be used for I/O operations submitted by kjournald2 during a
and sparse/thinly-provisioned LUNs, but it is off commit operation. This defaults to 3, which is a slightly higher
by default until sufficient testing has been done. priority than the default I/O priority.
nouid32 Disables 32-bit UIDs and GIDs. This is for auto_da_alloc(*), noauto_da_alloc
interoperability with older kernels which only Many broken applications don't use fsync() when replacing existing
store and expect 16-bit values. files via patterns such as fd = open("foo.new")/write(fd,..)/close(fd)/
rename("foo.new", "foo"), or worse yet, fd = open("foo",
O_TRUNC)/write(fd,..)/close(fd). If auto_da_alloc is enabled, ext4
will detect the replace-via-rename and replace-via-truncate patterns
and force that any delayed allocation blocks are allocated such that at
the next journal commit, in the default data=ordered mode, the data
blocks of the new file are forced to disk before the rename() operation
is committed. This provides roughly the same level of guarantees as
ext3, and avoids the "zero-length" problem that can happen when a
system crashes before the delayed allocation blocks are forced to disk.
block_validity(*) These options enable or disable the in-kernel noinit_itable
noblock_validity facility for tracking filesystem metadata blocks Do not initialize any uninitialized inode table blocks in the
within internal data structures. This allows multi- background. This feature may be used by installation CD's so that the
block allocator and other routines to notice install process can complete as quickly as possible; the inode table
bugs or corrupted allocation bitmaps which cause initialization process would then be deferred until the next time the
blocks to be allocated which overlap with file system is unmounted.
filesystem metadata blocks.
dioread_lock Controls whether or not ext4 should use the DIO read init_itable=n
dioread_nolock locking. If the dioread_nolock option is specified The lazy itable init code will wait n times the number of milliseconds
ext4 will allocate uninitialized extent before buffer it took to zero out the previous block group's inode table. This
write and convert the extent to initialized after IO minimizes the impact on the system performance while file system's
completes. This approach allows ext4 code to avoid inode table is being initialized.
using inode mutex, which improves scalability on high
speed storages. However this does not work with
data journaling and dioread_nolock option will be
ignored with kernel warning. Note that dioread_nolock
code path is only used for extent-based files.
Because of the restrictions this options comprises
it is off by default (e.g. dioread_lock).
max_dir_size_kb=n This limits the size of directories so that any discard, nodiscard(*)
attempt to expand them beyond the specified Controls whether ext4 should issue discard/TRIM commands to the
limit in kilobytes will cause an ENOSPC error. underlying block device when blocks are freed. This is useful for SSD
This is useful in memory constrained devices and sparse/thinly-provisioned LUNs, but it is off by default
environments, where a very large directory can until sufficient testing has been done.
cause severe performance problems or even
provoke the Out Of Memory killer. (For example,
if there is only 512mb memory available, a 176mb
directory may seriously cramp the system's style.)
i_version Enable 64-bit inode version support. This option is nouid32
off by default. Disables 32-bit UIDs and GIDs. This is for interoperability with
older kernels which only store and expect 16-bit values.
dax Use direct access (no page cache). See block_validity(*), noblock_validity
Documentation/filesystems/dax.txt. Note that These options enable or disable the in-kernel facility for tracking
this option is incompatible with data=journal. filesystem metadata blocks within internal data structures. This
======================= ======================================================= allows multi- block allocator and other routines to notice bugs or
corrupted allocation bitmaps which cause blocks to be allocated which
overlap with filesystem metadata blocks.
dioread_lock, dioread_nolock
Controls whether or not ext4 should use the DIO read locking. If the
dioread_nolock option is specified ext4 will allocate uninitialized
extent before buffer write and convert the extent to initialized after
IO completes. This approach allows ext4 code to avoid using inode
mutex, which improves scalability on high speed storages. However this
does not work with data journaling and dioread_nolock option will be
ignored with kernel warning. Note that dioread_nolock code path is only
used for extent-based files. Because of the restrictions this options
comprises it is off by default (e.g. dioread_lock).
max_dir_size_kb=n
This limits the size of directories so that any attempt to expand them
beyond the specified limit in kilobytes will cause an ENOSPC error.
This is useful in memory constrained environments, where a very large
directory can cause severe performance problems or even provoke the Out
Of Memory killer. (For example, if there is only 512mb memory
available, a 176mb directory may seriously cramp the system's style.)
i_version
Enable 64-bit inode version support. This option is off by default.
dax
Use direct access (no page cache). See
Documentation/filesystems/dax.txt. Note that this option is
incompatible with data=journal.
Data Mode Data Mode
========= =========
@ -407,11 +394,8 @@ in table below.
Files in /proc/fs/ext4/<devname> Files in /proc/fs/ext4/<devname>
================ ======= mb_groups
File Content details of multiblock allocator buddy cache of free blocks
================ =======
mb_groups details of multiblock allocator buddy cache of free blocks
================ =======
/sys entries /sys entries
============ ============
@ -426,74 +410,71 @@ Files in /sys/fs/ext4/<devname>:
(see also Documentation/ABI/testing/sysfs-fs-ext4) (see also Documentation/ABI/testing/sysfs-fs-ext4)
============================= ================================================= delayed_allocation_blocks
File Content 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
delayed_allocation_blocks This file is read-only and shows the number of allocated yet.
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
the goal inode used by the inode allocator in Tuning parameter which (if non-zero) controls the goal inode used by
preference to all other allocation heuristics. the inode allocator in preference to all other allocation heuristics.
This is intended for debugging use only, and This is intended for debugging use only, and should be 0 on production
should be 0 on production systems. systems.
inode_readahead_blks Tuning parameter which controls the maximum inode_readahead_blks
number of inode table blocks that ext4's inode Tuning parameter which controls the maximum number of inode table
table readahead algorithm will pre-read into blocks that ext4's inode table readahead algorithm will pre-read into
the buffer cache the buffer cache.
lifetime_write_kbytes This file is read-only and shows the number of lifetime_write_kbytes
kilobytes of data that have been written to this This file is read-only and shows the number of kilobytes of data that
filesystem since it was created. have been written to this filesystem since it was created.
max_writeback_mb_bump The maximum number of megabytes the writeback max_writeback_mb_bump
code will try to write out before move on to The maximum number of megabytes the writeback code will try to write
another inode. out before move on to another inode.
mb_group_prealloc The multiblock allocator will round up allocation mb_group_prealloc
requests to a multiple of this tuning parameter if The multiblock allocator will round up allocation requests to a
the stripe size is not set in the ext4 superblock multiple of this tuning parameter if the stripe size is not set in the
ext4 superblock
mb_max_to_scan The maximum number of extents the multiblock mb_max_to_scan
allocator will search to find the best extent The maximum number of extents the multiblock allocator will search to
find the best extent.
mb_min_to_scan The minimum number of extents the multiblock mb_min_to_scan
allocator will search to find the best extent The minimum number of extents the multiblock allocator will search to
find the best extent.
mb_order2_req Tuning parameter which controls the minimum size mb_order2_req
for requests (as a power of 2) where the buddy Tuning parameter which controls the minimum size for requests (as a
cache is used power of 2) where the buddy cache is used.
mb_stats Controls whether the multiblock allocator should mb_stats
collect statistics, which are shown during the Controls whether the multiblock allocator should collect statistics,
unmount. 1 means to collect statistics, 0 means which are shown during the unmount. 1 means to collect statistics, 0
not to collect statistics means not to collect statistics.
mb_stream_req Files which have fewer blocks than this tunable mb_stream_req
parameter will have their blocks allocated out Files which have fewer blocks than this tunable parameter will have
of a block group specific preallocation pool, so their blocks allocated out of a block group specific preallocation
that small files are packed closely together. pool, so that small files are packed closely together. Each large file
Each large file will have its blocks allocated will have its blocks allocated out of its own unique preallocation
out of its own unique preallocation pool. pool.
session_write_kbytes This file is read-only and shows the number of session_write_kbytes
kilobytes of data that have been written to this This file is read-only and shows the number of kilobytes of data that
filesystem since it was mounted. have been written to this filesystem since it was mounted.
reserved_clusters This is RW file and contains number of reserved reserved_clusters
clusters in the file system which will be used This is RW file and contains number of reserved clusters in the file
in the specific situations to avoid costly system which will be used in the specific situations to avoid costly
zeroout, unexpected ENOSPC, or possible data zeroout, unexpected ENOSPC, or possible data loss. The default is 2% or
loss. The default is 2% or 4096 clusters, 4096 clusters, whichever is smaller and this can be changed however it
whichever is smaller and this can be changed can never exceed number of clusters in the file system. If there is not
however it can never exceed number of clusters enough space for the reserved space when mounting the file mount will
in the file system. If there is not enough space _not_ fail.
for the reserved space when mounting the file
mount will _not_ fail.
============================= =================================================
Ioctls Ioctls
====== ======
@ -504,100 +485,80 @@ shown in the table below.
Table of Ext4 specific ioctls Table of Ext4 specific ioctls
============================= ================================================= EXT4_IOC_GETFLAGS
Ioctl Description Get additional attributes associated with inode. The ioctl argument is
============================= ================================================= an integer bitfield, with bit values described in ext4.h. This ioctl is
EXT4_IOC_GETFLAGS Get additional attributes associated with inode. an alias for FS_IOC_GETFLAGS.
The ioctl argument is an integer bitfield, with
bit values described in ext4.h. This ioctl is an
alias for FS_IOC_GETFLAGS.
EXT4_IOC_SETFLAGS Set additional attributes associated with inode. EXT4_IOC_SETFLAGS
The ioctl argument is an integer bitfield, with Set additional attributes associated with inode. The ioctl argument is
bit values described in ext4.h. This ioctl is an an integer bitfield, with bit values described in ext4.h. This ioctl is
alias for FS_IOC_SETFLAGS. an alias for FS_IOC_SETFLAGS.
EXT4_IOC_GETVERSION EXT4_IOC_GETVERSION, EXT4_IOC_GETVERSION_OLD
EXT4_IOC_GETVERSION_OLD Get the inode i_generation number stored for each inode. The
Get the inode i_generation number stored for i_generation number is normally changed only when new inode is created
each inode. The i_generation number is normally and it is particularly useful for network filesystems. The '_OLD'
changed only when new inode is created and it is version of this ioctl is an alias for FS_IOC_GETVERSION.
particularly useful for network filesystems. The
'_OLD' version of this ioctl is an alias for
FS_IOC_GETVERSION.
EXT4_IOC_SETVERSION EXT4_IOC_SETVERSION, EXT4_IOC_SETVERSION_OLD
EXT4_IOC_SETVERSION_OLD Set the inode i_generation number stored for each inode. The '_OLD'
Set the inode i_generation number stored for version of this ioctl is an alias for FS_IOC_SETVERSION.
each inode. The '_OLD' version of this ioctl
is an alias for FS_IOC_SETVERSION.
EXT4_IOC_GROUP_EXTEND This ioctl has the same purpose as the resize EXT4_IOC_GROUP_EXTEND
mount option. It allows to resize filesystem This ioctl has the same purpose as the resize mount option. It allows
to the end of the last existing block group, to resize filesystem to the end of the last existing block group,
further resize has to be done with resize2fs, further resize has to be done with resize2fs, either online, or
either online, or offline. The argument points offline. The argument points to the unsigned logn number representing
to the unsigned logn number representing the the filesystem new block count.
filesystem new block count.
EXT4_IOC_MOVE_EXT Move the block extents from orig_fd (the one EXT4_IOC_MOVE_EXT
this ioctl is pointing to) to the donor_fd (the Move the block extents from orig_fd (the one this ioctl is pointing to)
one specified in move_extent structure passed to the donor_fd (the one specified in move_extent structure passed as
as an argument to this ioctl). Then, exchange an argument to this ioctl). Then, exchange inode metadata between
inode metadata between orig_fd and donor_fd. orig_fd and donor_fd. This is especially useful for online
This is especially useful for online defragmentation, because the allocator has the opportunity to allocate
defragmentation, because the allocator has the moved blocks better, ideally into one contiguous extent.
opportunity to allocate moved blocks better,
ideally into one contiguous extent.
EXT4_IOC_GROUP_ADD Add a new group descriptor to an existing or EXT4_IOC_GROUP_ADD
new group descriptor block. The new group Add a new group descriptor to an existing or new group descriptor
descriptor is described by ext4_new_group_input block. The new group descriptor is described by ext4_new_group_input
structure, which is passed as an argument to structure, which is passed as an argument to this ioctl. This is
this ioctl. This is especially useful in especially useful in conjunction with EXT4_IOC_GROUP_EXTEND, which
conjunction with EXT4_IOC_GROUP_EXTEND, allows online resize of the filesystem to the end of the last existing
which allows online resize of the filesystem block group. Those two ioctls combined is used in userspace online
to the end of the last existing block group. resize tool (e.g. resize2fs).
Those two ioctls combined is used in userspace
online resize tool (e.g. resize2fs).
EXT4_IOC_MIGRATE This ioctl operates on the filesystem itself. EXT4_IOC_MIGRATE
It converts (migrates) ext3 indirect block mapped This ioctl operates on the filesystem itself. It converts (migrates)
inode to ext4 extent mapped inode by walking ext3 indirect block mapped inode to ext4 extent mapped inode by walking
through indirect block mapping of the original through indirect block mapping of the original inode and converting
inode and converting contiguous block ranges contiguous block ranges into ext4 extents of the temporary inode. Then,
into ext4 extents of the temporary inode. Then, inodes are swapped. This ioctl might help, when migrating from ext3 to
inodes are swapped. This ioctl might help, when ext4 filesystem, however suggestion is to create fresh ext4 filesystem
migrating from ext3 to ext4 filesystem, however and copy data from the backup. Note, that filesystem has to support
suggestion is to create fresh ext4 filesystem extents for this ioctl to work.
and copy data from the backup. Note, that
filesystem has to support extents for this ioctl
to work.
EXT4_IOC_ALLOC_DA_BLKS Force all of the delay allocated blocks to be EXT4_IOC_ALLOC_DA_BLKS
allocated to preserve application-expected ext3 Force all of the delay allocated blocks to be allocated to preserve
behaviour. Note that this will also start application-expected ext3 behaviour. Note that this will also start
triggering a write of the data blocks, but this triggering a write of the data blocks, but this behaviour may change in
behaviour may change in the future as it is the future as it is not necessary and has been done this way only for
not necessary and has been done this way only sake of simplicity.
for sake of simplicity.
EXT4_IOC_RESIZE_FS Resize the filesystem to a new size. The number EXT4_IOC_RESIZE_FS
of blocks of resized filesystem is passed in via Resize the filesystem to a new size. The number of blocks of resized
64 bit integer argument. The kernel allocates filesystem is passed in via 64 bit integer argument. The kernel
bitmaps and inode table, the userspace tool thus allocates bitmaps and inode table, the userspace tool thus just passes
just passes the new number of blocks. the new number of blocks.
EXT4_IOC_SWAP_BOOT Swap i_blocks and associated attributes EXT4_IOC_SWAP_BOOT
(like i_blocks, i_size, i_flags, ...) from Swap i_blocks and associated attributes (like i_blocks, i_size,
the specified inode with inode i_flags, ...) from the specified inode with inode EXT4_BOOT_LOADER_INO
EXT4_BOOT_LOADER_INO (#5). This is typically (#5). This is typically used to store a boot loader in a secure part of
used to store a boot loader in a secure part of the filesystem, where it can't be changed by a normal user by accident.
the filesystem, where it can't be changed by a The data blocks of the previous boot loader will be associated with the
normal user by accident. given inode.
The data blocks of the previous boot loader
will be associated with the given inode.
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References References
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