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

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

[Srivathsa Dara]

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
+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

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

[Darrick J. Wong]

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
> 
>