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From: Andreas Dilger <adilger@dilger.ca>
Message-Id: <4A52A838-688F-4B73-AFC9-7863469C5365@dilger.ca>
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Subject: Re: [External] : Re: [RESEND PATCH] e2fsprogs: misc/mke2fs.8.in:
 Correct valid cluster-size values
Date: Fri, 22 Mar 2024 17:10:15 -0600
In-Reply-To: <DM6PR10MB4347C97E2645B45A66CA0D76A02C2@DM6PR10MB4347.namprd10.prod.outlook.com>
Cc: Ext4 Developers List <linux-ext4@vger.kernel.org>,
 Theodore Ts'o <tytso@mit.edu>,
 Rajesh Sivaramasubramaniom <rajesh.sivaramasubramaniom@oracle.com>,
 Junxiao Bi <junxiao.bi@oracle.com>
To: Srivathsa Dara <srivathsa.d.dara@oracle.com>
References: <20240314093127.2100974-1-srivathsa.d.dara@oracle.com>
 <CE93B29C-6A50-46D2-95DA-956D1F6A4104@dilger.ca>
 <DM6PR10MB4347C97E2645B45A66CA0D76A02C2@DM6PR10MB4347.namprd10.prod.outlook.com>


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> On Mar 19, 2024, at 5:25 AM, Srivathsa Dara =
<srivathsa.d.dara@oracle.com> wrote:
>=20
> On March 16, 2024 3:02 AM, Andreas Dilger <adilger@dilger.ca> wrote:
>>=20
>> 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)
>>=20
>>=20
>> 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.
>=20
> Hi, Andreas. Thank you for the comment. Here are the details:

Thank you for this added information, but I guess my comment wasn't very =
clear.
*I* understand the background here.  My email was directed at your =
change to
the *man page*, where users who *do not* know the details go for =
information.

> The function ext2fs_new_range() is causing the error. This function =
gets
> called while creating the journal inode.
>=20
> Failure cases:
> ------------------------------------------
> A   | B   | C   | D   | E   | F     | len
> ------------------------------------------
> 1k    64m   0     16    16    65535    0
> 1k   128m   0     17    17    131071   0
> 1k   256m   0     18    18    262143   0
> 2k   128m   1     17    16    65535    0
> 2k   256m   1     18    17    131071   0
> 4k   256m   2     18    16    65535    0
>=20
> successful cases:
>=20
> 1k   32m    0     15    15    32767   32768
> 2k   64m    1     16    15    32767   32768
> 4k   128m   2     17    15    32767   32768

Basically, what I was asking is that your patch for the man page be =
updated to
include just a fraction of this information, specifically that it =
includes that
"the cluster size must be between 2-32768 times the filesystem =
blocksize" and
not just "based on the filesystem blocksize".

Cheers, Andreas


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