Subject: Re: stat64 for over 2TB file returned invalid st_blocks
From: Trond Myklebust <trond.myklebust@fys.uio.no>
To: Takashi Sato <sho@bsd.tnes.nec.co.jp>
Cc: Dave Kleikamp <shaggy@austin.ibm.com>,
       "'Andreas Dilger'" <adilger@clusterfs.com>,
       linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
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Date: Thu, 08 Dec 2005 09:27:23 -0500
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On Thu, 2005-12-08 at 20:38 +0900, Takashi Sato wrote:

> I prefer sector_t for i_blocks rather than newly defined blkcnt_t.
> The reasons are:
> 
>   - Both i_blocks and common sector_t are for on-disk 512-byte unit.
>     In this point of view, they have the same character.

One is a count of the number of blocks used by a file, and exists only
in order to help filesystems cache this value. The other is a handle to
a block. How is that the same?

>   - If we created the type blkcnt_t newly, the patch would have to
>     touch a lot of files as follows, like sector_t does.
>         block/Kconfig, asm-i386/types.h, asm-x86_64/types.h,
>         asm-ppc/types.h, asm-s390/types.h, asm-sh/types.h,
>         asm-h8300/types.h, asm-mips/types.h
>     It will be simple if we use sector_t for i_blocks.

That is not a particularly good reason.

> Also, I cannot imagine the situation that > 2TB files are used over
> network with CONFIG_LBD disabled kernel.  Is there such a thing
> realistically?

Apart from this and the kstat wart, there is no reason to set CONFIG_LBD
for a networked filesystem. Why would you want to buy a > 2TB local disk
on an HPC cluster node if you already have a server?

I suppose we can make NFS use a private field instead, and just set
i_blocks to 0, but that's unnecessarily wasteful too.

Cheers,
  Trond

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