ext4: update ext4 documentation (6f9524e9) · Commits · e / devices / android_kernel_oneplus_sm7250

Documentation/ABI/testing/sysfs-fs-ext4

+10 −3

Original line number	Diff line number	Diff line
		@@ -48,7 +48,7 @@ Description:
		will have its blocks allocated out of its own unique
		preallocation pool.

		What: /sys/fs/ext4/<disk>/inode_readahead
		What: /sys/fs/ext4/<disk>/inode_readahead_blks
		Date: March 2008
		Contact: "Theodore Ts'o" <tytso@mit.edu>
		Description:
		@@ -85,7 +85,14 @@ Date: June 2008
		Contact: "Theodore Ts'o" <tytso@mit.edu>
		Description:
		Tuning parameter which (if non-zero) controls the goal
		inode used by the inode allocator in p0reference to
		all other allocation hueristics. This is intended for
		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.

		What: /sys/fs/ext4/<disk>/max_writeback_mb_bump
		Date: September 2009
		Contact: "Theodore Ts'o" <tytso@mit.edu>
		Description:
		The maximum number of megabytes the writeback code will
		try to write out before move on to another inode.

Documentation/filesystems/ext4.txt

+206 −1

Original line number	Diff line number	Diff line
		@@ -373,6 +373,41 @@ nodiscard(*) commands to the underlying block device when
		and sparse/thinly-provisioned LUNs, but it is off
		by default until sufficient testing has been done.

		nouid32 Disables 32-bit UIDs and GIDs. This is for
		interoperability with older kernels which only
		store and expect 16-bit values.

		resize 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. It can be
		used only with conjunction with remount.

		block_validity This options allows to enables/disables the in-kernel
		noblock_validity facility for tracking filesystem metadata blocks
		within internal data structures. This allows multi-
		block allocator and other routines to quickly locate
		extents which might overlap with filesystem metadata
		blocks. This option is intended for debugging
		purposes and since it negatively affects the
		performance, it is off by default.

		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 nobh
		option and the mount will fail. Nor does it 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).

		i_version Enable 64-bit inode version support. This option is
		off by default.

		Data Mode
		=========
		There are 3 different data modes:
		@@ -400,6 +435,176 @@ needs to be read from and written to disk at the same time where it
		outperforms all others modes. Currently ext4 does not have delayed
		allocation support if this data journalling mode is selected.

		/proc entries
		=============

		Information about mounted ext4 file systems can be found in
		/proc/fs/ext4. Each mounted filesystem will have a directory in
		/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
		/proc/fs/ext4/dm-0). The files in each per-device directory are shown
		in table below.

		Files in /proc/fs/ext4/<devname>
		..............................................................................
		File Content
		mb_groups details of multiblock allocator buddy cache of free blocks
		..............................................................................

		/sys entries
		============

		Information about mounted ext4 file systems can be found in
		/sys/fs/ext4. Each mounted filesystem will have a directory in
		/sys/fs/ext4 based on its device name (i.e., /sys/fs/ext4/hdc or
		/sys/fs/ext4/dm-0). The files in each per-device directory are shown
		in table below.

		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.

		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

		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.

		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_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_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.

		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.
		..............................................................................

		Ioctls
		======

		There is some Ext4 specific functionality which can be accessed by applications
		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
		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_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_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_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_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.
		..............................................................................

		References
		==========