linux-ext4 - Re: [PATCH v2] e2fsprogs: misc/mke2fs.8.in: Correct valid cluster-size values

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Date: Mon, 25 Mar 2024 08:55:50 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Srivathsa Dara <srivathsa.d.dara@...cle.com>
Cc: linux-ext4@...r.kernel.org, adilger@...ger.ca,
	rajesh.sivaramasubramaniom@...cle.com, junxiao.bi@...cle.com
Subject: Re: [PATCH v2] e2fsprogs: misc/mke2fs.8.in: Correct valid
 cluster-size values

On Mon, Mar 25, 2024 at 10:36:21AM +0000, Srivathsa Dara wrote:
> According to the mke2fs man page, the supported cluster-size values
> for an ext4 filesystem are 2048 to 256M bytes. However, this is not
> the case.
> 
> When mkfs is run to create a filesystem with following specifications:
> * 1k blocksize and cluster-size greater than 32M
> * 2k blocksize and cluster-size greater than 64M
> * 4k blocksize and cluster-size greater than 128M
> mkfs fails with "Invalid argument passed to ext2 library while trying
> to create journal" error. In general, when the cluster-size to blocksize
> ratio is greater than 32k, mkfs fails with this error.
> 
> Went through the code and found out that the function
> `ext2fs_new_range()` is the source of this error. This is because when
> the cluster-size to blocksize ratio exceeds 32k, the length argument
> to the function `ext2fs_new_range()` results in 0. Hence, the error.
> 
> This patch corrects the valid cluster-size values.
> ---
>  misc/mke2fs.8.in | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/misc/mke2fs.8.in b/misc/mke2fs.8.in
> index 30f97bb5..8194cc41 100644
> --- a/misc/mke2fs.8.in
> +++ b/misc/mke2fs.8.in
> @@ -232,9 +232,9 @@ test is used instead of a fast read-only test.
>  .TP
>  .B \-C " cluster-size"
>  Specify the size of cluster in bytes for file systems using the bigalloc
> -feature.  Valid cluster-size values are from 2048 to 256M bytes per
> -cluster.  This can only be specified if the bigalloc feature is
> -enabled.  (See the
> +feature.  Valid cluster-size values range from 2 to 32768 times the
> +filesystem blocksize per cluster.  This can only be specified if the

I think it's redundant to say cluster twice in this sentence:

"The cluster size must be a power of two between 2 and 32768 times the
filesystem block size."

It's also worth mentioning that mkfs rounds the parameter down to the
nearest power of two, e.g. "-C 20k" gets you a 16k cluster size.

--D

> +bigalloc feature is enabled.  (See the
>  .B ext4 (5)
>  man page for more details about bigalloc.)   The default cluster size if
>  bigalloc is enabled is 16 times the block size.
> -- 
> 2.39.3
> 
>