linux-kernel - Re: EXPORT_SYMBOL(fat_get

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Message-ID: <20100817145403.GA28926@suse.de>
Date:	Tue, 17 Aug 2010 07:54:03 -0700
From:	Greg KH <gregkh@...e.de>
To:	Nelson Zhang <nxz@...ress.com>
Cc:	'David Cross' <david.cross@...ress.com>,
	hirofumi@...l.parknet.co.jp, linux-kernel@...r.kernel.org
Subject: Re: EXPORT_SYMBOL(fat_get_block)

On Mon, Aug 16, 2010 at 06:57:54AM +0800, Nelson Zhang wrote:
> Hi David, Greg,
> 
> What I have done so far is following:
> 
> 1. Open a file 
> 2. Seek to the end of file

That just created a "sparse file"

> What I have not done is:
> 
> 3. mmap the whole file. 
> 
> Without #3, the file is not allocated until I write to the file.

That is by design.

> I think we can try to use mmap to allocate the file but we still need
> a function that can get file block info once the file is allocated.

No, why would you want the file block info?

Just treat it as a file, using mmap() and all the other userspace
goodness that we have to get data to a file very quickly.  You don't
need to preallocate the file from userspace, or anything else like that.

I suggest looking at some documentation on how to use the Unix file apis
properly to implement this better.

thanks,

greg k-h
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