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Re: [PATCH 4/4] xfsprogs: zero out clean log in xfs_metadump

To: Brian Foster <bfoster@xxxxxxxxxx>
Subject: Re: [PATCH 4/4] xfsprogs: zero out clean log in xfs_metadump
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Wed, 03 Jun 2015 15:01:58 -0500
Cc: Eric Sandeen <sandeen@xxxxxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20150603171132.GD45447@xxxxxxxxxxxxxxx>
References: <5568B7CE.9030709@xxxxxxxxxx> <5568BB5C.4080400@xxxxxxxxxxx> <20150603171132.GD45447@xxxxxxxxxxxxxxx>
On 6/3/15 12:11 PM, Brian Foster wrote:
> On Fri, May 29, 2015 at 02:17:48PM -0500, Eric Sandeen wrote:
>> When doing an xfs_metadump, if the log is clean, zero it out
>> for 2 reasons:
>>
>>  * It'll make the image more compressible
>>  * It'll eliminate an un-obfuscated metadata source
>>
>> If the log isn't clean, and the user expected obfuscation, warn
>> that metadata in the log will not be obfuscated.
>>
>> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
>> ---
>>
>> diff --git a/db/metadump.c b/db/metadump.c
>> index bea4e00..eb5e9da 100644
>> --- a/db/metadump.c
>> +++ b/db/metadump.c
>> @@ -17,6 +17,7 @@
>>   */
>>  
>>  #include <libxfs.h>
>> +#include <libxlog.h>
>>  #include "bmap.h"
>>  #include "command.h"
>>  #include "metadump.h"
>> @@ -2169,6 +2170,8 @@ copy_sb_inodes(void)
>>  static int
>>  copy_log(void)
>>  {
>> +    int dirty;
>> +
>>      if (show_progress)
>>              print_progress("Copying log");
>>  
>> @@ -2180,6 +2183,31 @@ copy_log(void)
>>              print_warning("cannot read log");
>>              return !stop_on_read_error;
>>      }
>> +
>> +    dirty = xlog_is_dirty(mp, &x, 0);
>> +
>> +    switch (dirty) {
>> +    case 0:
>> +            /* clear out a clean log */
>> +            if (show_progress)
>> +                    print_progress("Zeroing clean log");
>> +            memset(iocur_top->data, 0,
>> +                    mp->m_sb.sb_logblocks * mp->m_sb.sb_blocksize);
> 
> Hmm, so is there any reason in the future we might want a metadump with
> a clean log matching what is actually on-disk? This is a debug tool
> after all. Perhaps this is mainly covered by the unclean and/or error
> cases, but that still seems like a potential loss of capability.
> 
> Anyways, I'm wondering if we should have an 'if (obfuscate)' here.
> Thoughts?

Yeah, I had thought about that too... now, why didn't I do it ... probably
worth doing, I'll send V2 unless I think of a reason not to :)

-Eric

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