From: Eric Sandeen <sandeen@redhat.com>
Subject: Re: [PATCH] mke2fs: further updates for mke2fs(8) man page
Date: Tue, 17 Dec 2013 09:11:18 -0600
Message-ID: <52B06996.5090005@redhat.com>
References: <1387268271-8285-1-git-send-email-adilger@dilger.ca>
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Cc: linux-ext4@vger.kernel.org
To: Andreas Dilger <adilger@dilger.ca>, tytso@mit.edu
In-Reply-To: <1387268271-8285-1-git-send-email-adilger@dilger.ca>
Sender: linux-ext4-owner@vger.kernel.org

On 12/17/13, 2:17 AM, Andreas Dilger wrote:
> The mke2fs(8) man page was updated in 4727c67dc2, but needs some
> more clear descriptions for extra_isize and metadta_csum features.
> The uninit_bg feature is supported by all ext4-capable kernels,
> and does have a slow e2fsck pass for newly-formatted filesystems,
> so remove the caveat.

Looks ok to me, but I think there's still one thing missing;
it mentions metadata checksums but nothing in the manpage says
how to turn those on, AFAICT:

$ grep -i2 "checksum\|csum\|crc" misc/mke2fs.8
.B uninit_bg
Create a filesystem without initializing all of the block groups.  This
feature also enables checksums and highest-inode-used statistics in each
blockgroup.  This feature can
speed up filesystem creation time noticeably (if lazy_itable_init is


(maybe I'm dense & missing it?)

-Eric

> Signed-off-by: Andreas Dilger <adilger@dilger.ca>
> ---
>  misc/mke2fs.8.in |   36 ++++++++++++++++++++++--------------
>  1 files changed, 22 insertions(+), 14 deletions(-)
> 
> diff --git a/misc/mke2fs.8.in b/misc/mke2fs.8.in
> index df244de..4486014 100644
> --- a/misc/mke2fs.8.in
> +++ b/misc/mke2fs.8.in
> @@ -210,8 +210,8 @@ in earlier versions of
>  .BR mke2fs .
>  The
>  .B \-R
> -option is still accepted for backwards compatibility.   The
> -following extended options are supported:
> +option is still accepted for backwards compatibility, but is deprecated.
> +The following extended options are supported:
>  .RS 1.2i
>  .TP
>  .BI mmp_update_interval= interval
> @@ -548,7 +548,7 @@ of e2fsprogs will not support file systems with this feature enabled.
>  .TP
>  .B bigalloc
>  .br
> -This feature enables clustered allocation, so that the unit of
> +This feature enables clustered block 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
> @@ -570,7 +570,7 @@ features be enabled.
>  .TP
>  .B dir_index
>  .br
> -Use hashed b-trees to speed up lookups in large directories.
> +Use hashed b-trees to speed up name lookups in large directories.
>  .TP
>  .B dir_nlink
>  .br
> @@ -590,8 +590,15 @@ 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.
> +This feature reserves a specific amount of space in each inode for
> +extended metadata such as nanosecond timestamps and file creation time,
> +even if the current kernel does not current need to reserve this much
> +space.  Without this feature, the kernel will reserve the amount of
> +space for features currently it currently needs, and the rest may be
> +consumed by extended attributes.
> +
> +For this feature to be useful the inode size must be 256 bytes in size
> +or larger.
>  .TP
>  .B ext_attr
>  .br
> @@ -649,10 +656,16 @@ set this feature automatically when a file > 2GiB is created.)
>  .\" .TP
>  .\" .B metadata_csum
>  .\" .br
> -.\" Filesystem supports metadata checksumming.  This feature enables a
> -.\" superset of the functionality of the
> +.\" Filesystem supports metadata checksumming.  This feature stores
> +.\" checksums for all of the filesystem metadata (superblock, group
> +.\" descriptor blocks, inode and block bitmaps, directories, and
> +.\" extent tree blocks).  The checksum algorithm used for the metadata
> +.\" blocks is different than the one used for group descriptors with the
>  .\" .B uninit_bg
> -.\" feature.
> +.\" feature, these two features are incompatible and
> +.\" .B metadata_csum
> +.\" will be used preferentially instead of
> +.\" .BR uninit_bg .
>  .\" .br
>  .\" .B Future feature, available in e2fsprogs 1.43-WIP
>  .TP
> @@ -719,11 +732,6 @@ 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.
>  .RE
>  .TP
>  .B \-q
>