I've added documentation for all defined features, including legacy and work in progress. * Some pre-existing feature explanations have been expanded based on ext4.wiki.kernel.org. * Future features (dirdata, ea_inode and metadata_csum) are commented out Regards, Uri Corin uri.corin@xxxxxxxxx --- diff --git a/misc/dumpe2fs.8.in b/misc/dumpe2fs.8.in index a493789..2cae930 100644 --- a/misc/dumpe2fs.8.in +++ b/misc/dumpe2fs.8.in @@ -68,7 +68,224 @@ print the detailed group information block numbers in hexadecimal format print the version number of .B dumpe2fs and exit. -.SH BUGS +.SH Features +Filesystem features as marked by +.B dumpe2fs. +.PP +.TP +.B 64bit +.br +Enables the file system to be larger than 2^32 blocks. This feature may be set +automatically, as needed. +.TP +.B bigalloc +.br +This feature enables clustered allocation, so that the unit of +allocation is a power of two number of blocks. That is, each bit in the +what had traditionally been known as the block allocation bitmap now +indicates whether a cluster is in use or not, where a cluster is by +default composed of 16 blocks. This feature can decrease the time +spent on doing block allocation and brings smaller fragmentation, especially +for large files. +.TP +.B compression +.br +Legacy feature, not settable by +.BR mke2fs (8) +and +.BR tune2fs (8) +.\" .TP +.\" .B dirdata +.\" .br +.\" Data in directory entry. +.\" .br +.\" Not implemented. +.TP +.B dir_index +.br +Filesystem Uses hashed b-trees to speed up lookups in large directories. +.TP +.B dir_nlink +.br +Allows more than 65000 subdirectories per directory. +.TP +.B dir_prealloc +.br +Block pre-allocation for new directories is enabled. +.\" .TP +.\" .B ea_inode +.\" .br +.\" Inodes can be used for large extended attributes. +.\" .br +.\" Not implemented. +.TP +.B extent +.br +Instead of using the indirect block scheme for storing the location of +data blocks in an inode, use extents instead. This is a much more +efficient encoding which speeds up filesystem access, especially for +large files. (Note: both +.B extent +and +.B extents +are accepted as valid names for this feature for +historical/backwards compatibility reasons.) +.TP +.B extra_isize +.br +This feature enables storage of nanosecond timestamps and creation +time, if the inode size is larger than 256 bytes or larger. +.TP +.B ext_attr +.br +This feature enables the use of extended attributes. +.TP +.B filetype +.br +This feature enables the storage file type information in directory +entries. It is normally enabled by default for all file system types. +.TP +.B flex_bg +.br +Allow the per-block group metadata (allocation bitmaps and inode tables) +to be placed anywhere on the storage media. In addition, +.B mke2fs +will place the per-block group metadata together starting at the first +block group of each "flex_bg group". The size of the flex_bg group +.TP +.B inline_data +.br +Allows small files or directories to be stored within the in-inode extended attribute area. +.TP +.B has_journal +.br +Uses a journal to ensure filesystem consistency even across unclean shutdowns. +.TP +.B huge_file +.br +Allows files larger than 2TiB in size. +.TP +.B imagic_inodes +.br +Legacy feature, not settable by +.BR mke2fs (8) +and +.BR tune2fs (8) +.TP +.B journal_dev +.br +This is a journal device +(see journal-options in +.BR tune2fs (8) +or +.BR mke2fs (8)). +.TP +.B large_dir +Supports large directory >2GiB or 3-level htree. +.TP +.B large_file +.br +Filesystem can contain files that are greater than 2GiB. (Modern kernels +set this feature automatically when a file > 2GiB is created.) +.TP +.B lazy_bg +.br +Legacy parameter for testing purposes, no longer supported by kernel. +.br +Allows an ext2/ext3 developer to create very large filesystems using sparse files where most of the block groups are not initialized and so do not require much disk space. +.TP +.B meta_bg +.br +This feature allows file systems to be resized on-line without explicitly +needing to reserve space for growth in the size of the block group +descriptors. This scheme is also used to resize file systems which are +larger than 2^32 blocks. It is not recommended that this feature be set +when a file system is created, since this alternate method of storing +the block group descriptor will slow down the time needed to mount the +file system, and newer kernels can automatically set this feature as +necessary when doing an online resize and no more reserved space is +available in the resize inode. +.\" .TP +.\" .B metadata_csum +.\" .br +.\" Filesystem supports metadata checksumming. This feature enables a +.\" superset of the functionality of the +.\" .B uninit_bg +.\" feature. +.\" .br +.\" .B Future feature, available in e2fsprogs 1.43-WIP +.TP +.B mmp +.br +Multiple mount protection (MMP) helps to protect the filesystem from being multiply mounted and is useful in shared storage environments. +.TP +.B needs_recovery +.br +This flag is set by the kernel to indicate either a mounted filesystem with +.B has_journal +is write enabled or, an unmounted filesystem is in an unclean state. +@QUOTA_MAN_COMMENT@.TP +@QUOTA_MAN_COMMENT@.B quota +@QUOTA_MAN_COMMENT@.br +@QUOTA_MAN_COMMENT@Create quota inodes (inode #3 for userquota and inode +@QUOTA_MAN_COMMENT@#4 for group quota) and set them in the superblock. +@QUOTA_MAN_COMMENT@With this feature, the quotas will be enabled +@QUOTA_MAN_COMMENT@automatically when the filesystem is mounted. +@QUOTA_MAN_COMMENT@.IP +@QUOTA_MAN_COMMENT@Causes the quota files (i.e., user.quota and +@QUOTA_MAN_COMMENT@group.quota which existed +@QUOTA_MAN_COMMENT@in the older quota design) to be hidden inodes. +@QUOTA_MAN_COMMENT@.IP +@QUOTA_MAN_COMMENT@.B Not defined by default, +@QUOTA_MAN_COMMENT@see https://ext4.wiki.kernel.org/index.php/Quota +.TP +.B replica +.br +Non-upstream feature. +.TP +.B resize_inode +.br +Reserves space so the block group descriptor table may grow in the future. +Useful for online resizing using +.BR resize2fs . +.TP +.B snapshot_bitmap +.br +Legacy parameter, no longer supported by kernel. +.TP + +.B sparse_super +.br +Filesystem has fewer superblock backup copies +(saves space on large filesystems). This feature is normally enabled by +default for all file systems. +.TP +.B uninit_bg +.br +Not all of the block groups are initialized. +This feature allows the kernel to initialize bitmaps and inode tables +and keep a high watermark for the unused inodes in a filesystem, to reduce +.BR e2fsck (8) +time. The result is that it can speed up filesystem creation time noticeably +(if lazy_itable_init is enabled). +.IP +This first e2fsck run after enabling this feature will take the +full time, but subsequent e2fsck runs will take only a fraction of the +original time, depending on how full the file system is. +It is only supported by the ext4 filesystem in recent Linux kernels. +.B sparse_super +.br +Limits the number of backup superblocks to save space on large filesystems. +.TP +.B uninit_bg, uninit_groups +.br +Allows the kernel to initialize bitmaps and inode tables and keep a high +watermark for the unused inodes in a filesystem, to reduce +.BR e2fsck (8) +time. +.br +The first e2fsck run after enabling this feature will take the full time, but subsequent e2fsck runs will take only a fraction of the original time, depending on how full the file system is. +SH BUGS You need to know the physical filesystem structure to understand the output. .SH AUTHOR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
