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Date: Mon, 16 Jan 2017 23:55:21 -0800
From: Christoph Hellwig <hch@infradead.org>
To: David Miller <davem@davemloft.net>
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Subject: Re: [PATCH RESEND] coredump: Ensure proper size of sparse core files
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On Mon, Jan 16, 2017 at 10:42:43PM -0500, David Miller wrote:
> The lseek() done by dump_skip() should extend the file properly.

lseek never extends a file.  It just moves the current file position.
So if you do not have a write after the lseek it does nothing.