use. On other operating systems, such as the GNU/HURD or FreeBSD, only
a very restrictive set of file system features may be supported in their
implementations of ext2.
-.RS 1.2i
.TP
.B 64bit
.br
.br
This ext4 feature allows more than 65000 subdirectories per directory.
.TP
+.B encrypt
+.br
+This ext4 feature provides file-system level encryption of data blocks
+and file names. The inode metadata (timestamps, file size, user/group
+ownership, etc.) is
+.I not
+encrypted.
+.IP
+This feature is most useful on file systems with multiple users, or
+where not all files should be encrypted. In many use cases, especially
+on single-user systems, encryption at the block device layer using
+dm-crypt may provide much better security.
+.TP
.B ext_attr
.br
This feature enables the use of extended attributes. This feature is
and it also speeds up the time required for
.BR mke2fs (8)
to create the file system.
-.RE
.SH MOUNT OPTIONS
This section describes mount options which are specific to ext2, ext3,
and ext4. Other generic mount options may be used as well; see
For descriptions of these attribute flags, please refer to the
.BR chattr (1)
man page.
+.SH KERNEL SUPPORT
+This section lists the file system driver (e.g., ext2, ext3, ext4) and
+upstream kernel version where a particular file system feature was
+supported. Note that in some cases the feature was present in earlier
+kernel versions, but there were known, serious bugs. In other cases the
+feature may still be considered in an experimental state. Finally, note
+that some distributions may have backported features into older kernels;
+in particular the kernel versions in certain "enterprise distributions"
+can be extremely misleading.
+.IP "\fBfiletype\fR" 2in
+ext2, 2.2.0
+.IP "\fBsparse_super\fR" 2in
+ext2, 2.2.0
+.IP "\fBlarge_file\fR" 2in
+ext2, 2.2.0
+.IP "\fBhas_journal\fR" 2in
+ext3, 2.4.15
+.IP "\fBext_attr\fR" 2in
+ext2/ext3, 2.6.0
+.IP "\fBdir_index\fR" 2in
+ext3, 2.6.0
+.IP "\fBresize_inode\fR" 2in
+ext3, 2.6.10 (online resizing)
+.IP "\fB64bit\fR" 2in
+ext4, 2.6.28
+.IP "\fBdir_nlink\fR" 2in
+ext4, 2.6.28
+.IP "\fBextent\fR" 2in
+ext4, 2.6.28
+.IP "\fBextra_isize\fR" 2in
+ext4, 2.6.28
+.IP "\fBflex_bg\fR" 2in
+ext4, 2.6.28
+.IP "\fBhuge_file\fR" 2in
+ext4, 2.6.28
+.IP "\fBmeta_bg\fR" 2in
+ext4, 2.6.28
+.IP "\fBuninit_bg\fR" 2in
+ext4, 2.6.28
+.IP "\fBmmp\fR" 2in
+ext4, 3.0
+.IP "\fBbigalloc\fR" 2in
+ext4, 3.2
+.IP "\fBquota\fR" 2in
+ext4, 3.6
+.IP "\fBinline_data\fR" 2in
+ext4, 3.8
+.IP "\fBsparse_super2\fR" 2in
+ext4, 3.16
+.IP "\fBmetdata_csum\fR" 2in
+ext4, 3.18
+.IP "\fBencrypt\fR" 2in
+ext4, 4.1
+.IP "\fBproject\fR" 2in
+ext4, 4.5
.SH SEE ALSO
.BR mke2fs (8),
.BR mke2fs.conf (5),