linux-ext4 - Re: Problems with the max value for create directory

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Message-id: <20081223074944.GH5000@webber.adilger.int>
Date:	Tue, 23 Dec 2008 00:49:44 -0700
From:	Andreas Dilger <adilger@....com>
To:	Toshiyuki Okajima <toshi.okajima@...fujitsu.com>
Cc:	Zhang Xiliang <zhangxiliang@...fujitsu.com>,
	linux-ext4@...r.kernel.org
Subject: Re: Problems with the max value for create directory

On Dec 23, 2008  13:02 +0900, Toshiyuki Okajima wrote:
> Zhang Xiliang wrote:
>> Hi,
>>
>> I creat 65537 long directories and failed when the block size is 1024.
>>
>> # mkfs.ext4dev -b 1024 -I 256 /dev/hda3
>> # tune2fs -E test_fs -O extents /dev/hda3
>> # mount -t ext4dev /dev/hda3 /mnt
>> # ./create_long_dirs 65537 /mnt
>>
>> The code of create_long_dirs.c:
>
> ext4 filesystem cannot make over 65000 links toward a file.
> (ext3 filesystem cannot make over 32000 links toward a file.)
> This test makes over 65000 links toward /mnt-directory.
> (Creating 65000 sub-directories makes 65000 links toward /mnt-directory.)

Note that there is a specific reason why it was implemented this way:
- a directory with > 65000 subdirectories can be checked if empty even
  if the link count is wrong (in fact link count was ignored even in ext3)
- a file needs to keep accurate link counts or it is impossible to know
  when the file needs to be deleted.

We thought about adding a "i_links_count_hi" but it wasn't thought that
many (any) real applications would create so many hard links on the same
file.


Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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