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From: Andreas Dilger <adilger@dilger.ca>
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Subject: Re: [RESEND PATCH] e2fsprogs: misc/mke2fs.8.in: Correct valid
 cluster-size values
Date: Fri, 15 Mar 2024 15:32:17 -0600
In-Reply-To: <20240314093127.2100974-1-srivathsa.d.dara@oracle.com>
Cc: Ext4 Developers List <linux-ext4@vger.kernel.org>,
 Theodore Ts'o <tytso@mit.edu>,
 rajesh.sivaramasubramaniom@oracle.com,
 junxiao.bi@oracle.com
To: Srivathsa Dara <srivathsa.d.dara@oracle.com>
References: <20240314093127.2100974-1-srivathsa.d.dara@oracle.com>


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On Mar 14, 2024, at 3:31 AM, Srivathsa Dara =
<srivathsa.d.dara@oracle.com> wrote:
>=20
> 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.
>=20
> 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.
>=20
> 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.
>=20
> This patch corrects the valid cluster-size values.
> ---
> misc/mke2fs.8.in | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>=20
> diff --git a/misc/mke2fs.8.in b/misc/mke2fs.8.in
> index e6bfc6d6..b5b02144 100644
> --- a/misc/mke2fs.8.in
> +++ b/misc/mke2fs.8.in
> @@ -230,9 +230,9 @@ test is used instead of a fast read-only test.
> .TP
> .B \-C " cluster-size"
> Specify the size of cluster in bytes for filesystems 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 are from 2048 to 128M bytes per
> +cluster based on filesystem blocksize. This can only be specified if =
the
> +bigalloc feature is enabled.  (See the
> .B ext4 (5)


This is an improvement, but doesn't really explain the details of the
limits.  Instead of "based on filesystem blocksize." I think writing
"between 2-32768 times the filesystem blocksize." or similar would be
more clear and explain how the actual limits relate to the blocksize.

Cheers, Andreas


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