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Re: [PATCH RESEND] coredump: Ensure proper size of sparse core files

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  Re: [PATCH RESEND] coredump: Ensure proper size of sparse core  files David Miller <davem@davemloft.net> - 2017-01-17 04:50 +0100
    Re: [PATCH RESEND] coredump: Ensure proper size of sparse core files Christoph Hellwig <hch@infradead.org> - 2017-01-17 09:00 +0100
      Re: [PATCH RESEND] coredump: Ensure proper size of sparse core  files David Miller <davem@davemloft.net> - 2017-01-17 21:50 +0100
        Re: [PATCH RESEND] coredump: Ensure proper size of sparse core files Dave Kleikamp <dave.kleikamp@oracle.com> - 2017-01-17 22:10 +0100

#1560239 — Re: [PATCH RESEND] coredump: Ensure proper size of sparse core files

From: Dave Kleikamp <dave.kleikamp@oracle.com>
Date: Wed, 11 Jan 2017 13:25:00 -0600

> If the last section of a core file ends with an unmapped or zero page,
> the size of the file does not correspond with the last dump_skip() call.
> gdb complains that the file is truncated and can be confusing to users.
> 
> After all of the vma sections are written, make sure that the file size
> is no smaller than the current file position.
> 
> This problem can be demonstrated with gdb's bigcore testcase on the
> sparc architecture.
> 
> Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>

The lseek() done by dump_skip() should extend the file properly.

Otherwise, everyone would be seeing this problem.

That test case passed all the time when I was last running the GDB
testsuite all the time on sparc64, say 5 years ago.

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#1560310 — Re: [PATCH RESEND] coredump: Ensure proper size of sparse core files

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.

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#1561007

From: Christoph Hellwig <hch@infradead.org>
Date: Mon, 16 Jan 2017 23:55:21 -0800

> 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.

Ok, then the only other feedback I have is that we should probably
defer this truncate() call until the last possible dump write occurs
rather than right after the VMA loop.

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#1561021 — Re: [PATCH RESEND] coredump: Ensure proper size of sparse core files

On 01/17/2017 02:44 PM, David Miller wrote:
> From: Christoph Hellwig <hch@infradead.org>
> Date: Mon, 16 Jan 2017 23:55:21 -0800
> 
>> 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.
> 
> Ok, then the only other feedback I have is that we should probably
> defer this truncate() call until the last possible dump write occurs
> rather than right after the VMA loop.

Yeah. That's fine with me.

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