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docs: make ext4 readme tables readable

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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:
(*) == 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
mount options "ro,noload" can be used to prevent
writes to the filesystem.
ro
Mount filesystem read only. Note that ext4 will 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.
This will allow the recovery code in e2fsck and the
kernel to detect corruption in the kernel. It is a
compatible change and will be ignored by older kernels.
journal_checksum
Enable checksumming of the journal transactions. This will allow the
recovery code in e2fsck and the kernel to detect corruption in the
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
for descriptor blocks. If enabled older kernels cannot
mount the device. This will enable 'journal_checksum'
internally.
journal_async_commit
Commit block can be written to disk without waiting for descriptor
blocks. If enabled older kernels cannot mount the device. This will
enable 'journal_checksum' internally.
journal_path=path
journal_dev=devnum When the external journal device's major/minor numbers
have changed, these options allow the user to specify
the new journal location. The journal device is
identified through either its new major/minor numbers
encoded in devnum, or via a path to the device.
journal_path=path, journal_dev=devnum
When the external journal device's major/minor numbers have changed,
these options allow the user to specify the new journal location. The
journal device is identified through either its new major/minor numbers
encoded in devnum, or via a path to the device.
norecovery Don't load the journal on mounting. Note that
noload if the filesystem was not unmounted cleanly,
skipping the journal replay will lead to the
filesystem containing inconsistencies that can
lead to any number of problems.
norecovery, noload
Don't load the journal on mounting. Note that if the filesystem was
not unmounted cleanly, skipping the journal replay will lead to the
filesystem containing inconsistencies that can lead to any number of
problems.
data=journal All data are committed into the journal prior to being
written into the main file system. Enabling
this mode will disable delayed allocation and
O_DIRECT support.
data=journal
All data are committed into the journal prior to being written into the
main file system. Enabling this mode will disable delayed allocation
and O_DIRECT support.
data=ordered (*) All data are forced directly out to the main file
system prior to its metadata being committed to the
journal.
data=ordered (*)
All data are forced directly out to the main file system prior to its
metadata being committed to the journal.
data=writeback Data ordering is not preserved, data may be written
into the main file system after its metadata has been
committed to the journal.
data=writeback
Data ordering is not preserved, data may be written into the main file
system after its metadata has been committed to the journal.
commit=nrsec (*) Ext4 can be told to sync all its data and metadata
every 'nrsec' seconds. The default value is 5 seconds.
This means that if you lose your power, you will lose
as much as the latest 5 seconds of work (your
filesystem will not be damaged though, thanks to the
journaling). This default value (or any low value)
will hurt performance, but it's good for data-safety.
Setting it to 0 will have the same effect as leaving
it at the default (5 seconds).
Setting it to very large values will improve
performance.
commit=nrsec (*)
Ext4 can be told to sync all its data and metadata every 'nrsec'
seconds. The default value is 5 seconds. This means that if you lose
your power, you will lose as much as the latest 5 seconds of work (your
filesystem will not be damaged though, thanks to the journaling). This
default value (or any low value) will hurt performance, but it's good
for data-safety. Setting it to 0 will have the same effect as leaving
it at the default (5 seconds). Setting it to very large values will
improve performance.
barrier=<0|1(*)> This enables/disables the use of write barriers in
barrier(*) the jbd code. barrier=0 disables, barrier=1 enables.
nobarrier This also requires an IO stack which can support
barriers, and if jbd gets an error on a barrier
write, it will disable again with a warning.
Write barriers enforce proper on-disk ordering
of journal commits, making volatile disk write caches
safe to use, at some performance penalty. If
your disks are battery-backed in one way or another,
disabling barriers may safely improve performance.
The mount options "barrier" and "nobarrier" can
also be used to enable or disable barriers, for
consistency with other ext4 mount options.
barrier=<0|1(*)>, barrier(*), nobarrier
This enables/disables the use of write barriers in the jbd code.
barrier=0 disables, barrier=1 enables. This also requires an IO stack
which can support barriers, and if jbd gets an error on a barrier
write, it will disable again with a warning. Write barriers enforce
proper on-disk ordering of journal commits, making volatile disk write
caches safe to use, at some performance penalty. If your disks are
battery-backed in one way or another, disabling barriers may safely
improve performance. The mount options "barrier" and "nobarrier" can
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
number of inode table blocks that ext4's inode
table readahead algorithm will pre-read into
the buffer cache. The default value is 32 blocks.
inode_readahead_blks=n
This tuning parameter controls the maximum number of inode table blocks
that ext4's inode table readahead algorithm will pre-read into the
buffer cache. The default value is 32 blocks.
nouser_xattr Disables Extended User Attributes. See the
attr(5) manual page for more information about
extended attributes.
nouser_xattr
Disables Extended User Attributes. See the attr(5) manual page for
more information about extended attributes.
noacl This option disables POSIX Access Control List
support. If ACL support is enabled in the kernel
configuration (CONFIG_EXT4_FS_POSIX_ACL), ACL is
enabled by default on mount. See the acl(5) manual
page for more information about acl.
noacl
This option disables POSIX Access Control List support. If ACL support
is enabled in the kernel configuration (CONFIG_EXT4_FS_POSIX_ACL), ACL
is enabled by default on mount. See the acl(5) manual page for more
information about acl.
bsddf (*) Make 'df' act like BSD.
minixdf Make 'df' act like Minix.
bsddf (*)
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
debugging purposes. This is normally used while
remounting a filesystem which is already mounted.
debug
Extra debugging information is sent to syslog.
errors=remount-ro Remount the filesystem read-only on an error.
errors=continue Keep going on a filesystem error.
errors=panic 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)
abort
Simulate the effects of calling ext4_abort() for debugging purposes.
This is normally used while remounting a filesystem which is already
mounted.
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.
errors=remount-ro
Remount the filesystem read-only on an error.
grpid New objects have the group ID of their parent.
bsdgroups
errors=continue
Keep going on a filesystem error.
nogrpid (*) New objects have the group ID of their creator.
sysvgroups
errors=panic
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
noquota are used only by quota tools to recognize volumes
grpquota where quota should be turned on. See documentation
usrquota in the quota-tools package for more details
(http://sourceforge.net/projects/linuxquota).
resgid=n
The group ID which may use the reserved blocks.
jqfmt=<quota type> These options tell filesystem details about quota
usrjquota=<file> so that quota information can be properly updated
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).
resuid=n
The user ID which may use the reserved blocks.
stripe=n Number of filesystem blocks that mballoc will try
to use for allocation size and alignment. For RAID5/6
systems this should be the number of data
disks * RAID chunk size in file system blocks.
sb=
Use alternate superblock at this location.
delalloc (*) Defer block allocation until just before ext4
writes out the block(s) in question. This
allows ext4 to better allocation decisions
more efficiently.
nodelalloc Disable delayed allocation. Blocks are allocated
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.
quota, noquota, grpquota, usrquota
These options are ignored by the filesystem. They are used only by
quota tools to recognize volumes where quota should be turned on. See
documentation in the quota-tools package for more details
(http://sourceforge.net/projects/linuxquota).
max_batch_time=usec Maximum amount of time ext4 should wait for
additional filesystem operations to be batch
together with a synchronous write operation.
Since a synchronous write operation is going to
force a commit and then a wait for the I/O
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.
jqfmt=<quota type>, usrjquota=<file>, grpjquota=<file>
These options tell filesystem details about quota so that quota
information can be properly updated during journal replay. They replace
the above quota options. See documentation in the quota-tools package
for more details (http://sourceforge.net/projects/linuxquota).
min_batch_time=usec This parameter sets the commit time (as
described above) to be at least min_batch_time.
It defaults to zero microseconds. Increasing
this parameter may improve the throughput of
multi-threaded, synchronous workloads on very
fast disks, at the cost of increasing latency.
stripe=n
Number of filesystem blocks that mballoc will try to use for allocation
size and alignment. For RAID5/6 systems this should be the number of
data disks * RAID chunk size in file system blocks.
journal_ioprio=prio The I/O priority (from 0 to 7, where 0 is the
highest priority) which should be used for I/O
operations submitted by kjournald2 during a
commit operation. This defaults to 3, which is
a slightly higher priority than the default I/O
priority.
delalloc (*)
Defer block allocation until just before ext4 writes out the block(s)
in question. This allows ext4 to better allocation decisions more
efficiently.
auto_da_alloc(*) Many broken applications don't use fsync() when
noauto_da_alloc replacing existing 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.
nodelalloc
Disable delayed allocation. Blocks are allocated 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.
noinit_itable Do not initialize any uninitialized inode table
blocks in the background. This feature may be
used by installation CD's so that the install
process can complete as quickly as possible; the
inode table initialization process would then be
deferred until the next time the file system
is unmounted.
max_batch_time=usec
Maximum amount of time ext4 should wait for additional filesystem
operations to be batch together with a synchronous write operation.
Since a synchronous write operation is going to force a commit and then
a wait for the I/O 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.
init_itable=n The lazy itable init code will wait n times the
number of milliseconds it took to zero out the
previous block group's inode table. This
minimizes the impact on the system performance
while file system's inode table is being initialized.
min_batch_time=usec
This parameter sets the commit time (as described above) to be at least
min_batch_time. It defaults to zero microseconds. Increasing this
parameter may improve the throughput of multi-threaded, synchronous
workloads on very fast disks, at the cost of increasing latency.
discard Controls whether ext4 should issue discard/TRIM
nodiscard(*) commands to the underlying block device when
blocks are freed. This is useful for SSD devices
and sparse/thinly-provisioned LUNs, but it is off
by default until sufficient testing has been done.
journal_ioprio=prio
The I/O priority (from 0 to 7, where 0 is the highest priority) which
should be used for I/O operations submitted by kjournald2 during a
commit operation. This defaults to 3, which is a slightly higher
priority than the default I/O priority.
nouid32 Disables 32-bit UIDs and GIDs. This is for
interoperability with older kernels which only
store and expect 16-bit values.
auto_da_alloc(*), noauto_da_alloc
Many broken applications don't use fsync() when replacing existing
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
noblock_validity facility for tracking 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.
noinit_itable
Do not initialize any uninitialized inode table blocks in the
background. This feature may be used by installation CD's so that the
install process can complete as quickly as possible; the inode table
initialization process would then be deferred until the next time the
file system is unmounted.
dioread_lock Controls whether or not ext4 should use the DIO read
dioread_nolock 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).
init_itable=n
The lazy itable init code will wait n times the number of milliseconds
it took to zero out the previous block group's inode table. This
minimizes the impact on the system performance while file system's
inode table is being initialized.
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.)
discard, nodiscard(*)
Controls whether ext4 should issue discard/TRIM commands to the
underlying block device when blocks are freed. This is useful for SSD
devices and sparse/thinly-provisioned LUNs, but it is off by default
until sufficient testing has been done.
i_version Enable 64-bit inode version support. This option is
off by default.
nouid32
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
Documentation/filesystems/dax.txt. Note that
this option is incompatible with data=journal.
======================= =======================================================
block_validity(*), noblock_validity
These options enable or disable the in-kernel facility for tracking
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
=========
@ -407,11 +394,8 @@ in table below.
Files in /proc/fs/ext4/<devname>
================ =======
File Content
================ =======
mb_groups details of multiblock allocator buddy cache of free blocks
================ =======
mb_groups
details of multiblock allocator buddy cache of free blocks
/sys entries
============
@ -426,74 +410,71 @@ Files in /sys/fs/ext4/<devname>:
(see also Documentation/ABI/testing/sysfs-fs-ext4)
============================= =================================================
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.
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
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_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
number of inode table blocks that ext4's inode
table readahead algorithm will pre-read into
the buffer cache
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
kilobytes of data that have been written to this
filesystem since it was created.
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.
max_writeback_mb_bump The maximum number of megabytes the writeback
code will try to write out before move on to
another inode.
max_writeback_mb_bump
The maximum number of megabytes the writeback code will try to write
out before move on to another inode.
mb_group_prealloc The multiblock allocator will round up allocation
requests to a multiple of this tuning parameter if
the stripe size is not set in the ext4 superblock
mb_group_prealloc
The multiblock allocator will round up allocation requests to a
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
allocator will search to find the best extent
mb_max_to_scan
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
allocator will search to find the best extent
mb_min_to_scan
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
for requests (as a power of 2) where the buddy
cache is used
mb_order2_req
Tuning parameter which controls the minimum size for requests (as a
power of 2) where the buddy cache is used.
mb_stats Controls whether the multiblock allocator should
collect statistics, which are shown during the
unmount. 1 means to collect statistics, 0 means
not to collect statistics
mb_stats
Controls whether the multiblock allocator should collect statistics,
which are shown during the unmount. 1 means to collect statistics, 0
means not to collect statistics.
mb_stream_req Files which have fewer blocks than this tunable
parameter will have their blocks allocated out
of a block group specific preallocation pool, so
that small files are packed closely together.
Each large file will have its blocks allocated
out of its own unique preallocation pool.
mb_stream_req
Files which have fewer blocks than this tunable parameter will have
their blocks allocated out of a block group specific preallocation
pool, so that small files are packed closely together. Each large file
will have its blocks allocated out of its own unique preallocation
pool.
session_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 mounted.
session_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 mounted.
reserved_clusters This is RW file and contains number of reserved
clusters in the file system which will be used
in the specific situations to avoid costly
zeroout, unexpected ENOSPC, or possible data
loss. The default is 2% or 4096 clusters,
whichever is smaller and this can be changed
however it can never exceed number of clusters
in the file system. If there is not enough space
for the reserved space when mounting the file
mount will _not_ fail.
============================= =================================================
reserved_clusters
This is RW file and contains number of reserved clusters in the file
system which will be used in the specific situations to avoid costly
zeroout, unexpected ENOSPC, or possible data loss. The default is 2% or
4096 clusters, whichever is smaller and this can be changed however it
can never exceed number of clusters in the file system. If there is not
enough space for the reserved space when mounting the file mount will
_not_ fail.
Ioctls
======
@ -504,100 +485,80 @@ shown in the table below.
Table of Ext4 specific ioctls
============================= =================================================
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
alias for FS_IOC_GETFLAGS.
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 alias for FS_IOC_GETFLAGS.
EXT4_IOC_SETFLAGS Set additional attributes associated with inode.
The ioctl argument is an integer bitfield, with
bit values described in ext4.h. This ioctl is an
alias for FS_IOC_SETFLAGS.
EXT4_IOC_SETFLAGS
Set additional attributes associated with inode. The ioctl argument is
an integer bitfield, with bit values described in ext4.h. This ioctl is
an alias for FS_IOC_SETFLAGS.
EXT4_IOC_GETVERSION
EXT4_IOC_GETVERSION_OLD
Get the inode i_generation number stored for
each inode. The i_generation number is normally
changed only when new inode is created and it is
particularly useful for network filesystems. The
'_OLD' version of this ioctl is an alias for
FS_IOC_GETVERSION.
EXT4_IOC_GETVERSION, EXT4_IOC_GETVERSION_OLD
Get the inode i_generation number stored for each inode. The
i_generation number is normally changed only when new inode is created
and it is particularly useful for network filesystems. The '_OLD'
version of this ioctl is an alias for FS_IOC_GETVERSION.
EXT4_IOC_SETVERSION
EXT4_IOC_SETVERSION_OLD
Set the inode i_generation number stored for
each inode. The '_OLD' version of this ioctl
is an alias for FS_IOC_SETVERSION.
EXT4_IOC_SETVERSION, EXT4_IOC_SETVERSION_OLD
Set the inode i_generation number stored for 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
mount option. It allows to resize filesystem
to the end of the last existing block group,
further resize has to be done with resize2fs,
either online, or offline. The argument points
to the unsigned logn number representing the
filesystem new block count.
EXT4_IOC_GROUP_EXTEND
This ioctl has the same purpose as the resize mount option. It allows
to resize filesystem to the end of the last existing block group,
further resize has to be done with resize2fs, either online, or
offline. The argument points to the unsigned logn number representing
the filesystem new block count.
EXT4_IOC_MOVE_EXT Move the block extents from orig_fd (the one
this ioctl is pointing to) to the donor_fd (the
one specified in move_extent structure passed
as an argument to this ioctl). Then, exchange
inode metadata between orig_fd and donor_fd.
This is especially useful for online
defragmentation, because the allocator has the
opportunity to allocate moved blocks better,
ideally into one contiguous extent.
EXT4_IOC_MOVE_EXT
Move the block extents from orig_fd (the one this ioctl is pointing to)
to the donor_fd (the one specified in move_extent structure passed as
an argument to this ioctl). Then, exchange inode metadata between
orig_fd and donor_fd. This is especially useful for online
defragmentation, because the allocator has the opportunity to allocate
moved blocks better, ideally into one contiguous extent.
EXT4_IOC_GROUP_ADD Add a new group descriptor to an existing or
new group descriptor block. The new group
descriptor is described by ext4_new_group_input
structure, which is passed as an argument to
this ioctl. This is especially useful in
conjunction with EXT4_IOC_GROUP_EXTEND,
which allows online resize of the filesystem
to the end of the last existing block group.
Those two ioctls combined is used in userspace
online resize tool (e.g. resize2fs).
EXT4_IOC_GROUP_ADD
Add a new group descriptor to an existing or new group descriptor
block. The new group descriptor is described by ext4_new_group_input
structure, which is passed as an argument to this ioctl. This is
especially useful in conjunction with EXT4_IOC_GROUP_EXTEND, which
allows online resize of the filesystem to the end of the last existing
block group. Those two ioctls combined is used in userspace online
resize tool (e.g. resize2fs).
EXT4_IOC_MIGRATE This ioctl operates on the filesystem itself.
It converts (migrates) ext3 indirect block mapped
inode to ext4 extent mapped inode by walking
through indirect block mapping of the original
inode and converting contiguous block ranges
into ext4 extents of the temporary inode. Then,
inodes are swapped. This ioctl might help, when
migrating from ext3 to ext4 filesystem, however
suggestion is to create fresh ext4 filesystem
and copy data from the backup. Note, that
filesystem has to support extents for this ioctl
to work.
EXT4_IOC_MIGRATE
This ioctl operates on the filesystem itself. It converts (migrates)
ext3 indirect block mapped inode to ext4 extent mapped inode by walking
through indirect block mapping of the original inode and converting
contiguous block ranges into ext4 extents of the temporary inode. Then,
inodes are swapped. This ioctl might help, when migrating from ext3 to
ext4 filesystem, however suggestion is to create fresh ext4 filesystem
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
allocated to preserve application-expected ext3
behaviour. Note that this will also start
triggering a write of the data blocks, but this
behaviour may change in the future as it is
not necessary and has been done this way only
for sake of simplicity.
EXT4_IOC_ALLOC_DA_BLKS
Force all of the delay allocated blocks to be allocated to preserve
application-expected ext3 behaviour. Note that this will also start
triggering a write of the data blocks, but this behaviour may change in
the future as it is not necessary and has been done this way only for
sake of simplicity.
EXT4_IOC_RESIZE_FS Resize the filesystem to a new size. The number
of blocks of resized filesystem is passed in via
64 bit integer argument. The kernel allocates
bitmaps and inode table, the userspace tool thus
just passes the new number of blocks.
EXT4_IOC_RESIZE_FS
Resize the filesystem to a new size. The number of blocks of resized
filesystem is passed in via 64 bit integer argument. The kernel
allocates bitmaps and inode table, the userspace tool thus just passes
the new number of blocks.
EXT4_IOC_SWAP_BOOT Swap i_blocks and associated attributes
(like i_blocks, i_size, i_flags, ...) from
the specified inode with inode
EXT4_BOOT_LOADER_INO (#5). This is typically
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 data blocks of the previous boot loader
will be associated with the given inode.
============================= =================================================
EXT4_IOC_SWAP_BOOT
Swap i_blocks and associated attributes (like i_blocks, i_size,
i_flags, ...) from the specified inode with inode EXT4_BOOT_LOADER_INO
(#5). This is typically 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 data blocks of the previous boot loader will be associated with the
given inode.
References
==========