Re: [PATCH] tmpfs: support SEEK_DATA and SEEK_HOLE (reprise)

[Jeff Liu <jeff.liu@oracle.com>]

On 11/29/2012 12:15 PM, Jim Meyering wrote:
> Hugh Dickins wrote:
>> On Thu, 29 Nov 2012, Jaegeuk Hanse wrote:
> ...
>>> But this time in which scenario will use it?
>>
>> I was not very convinced by the grep argument from Jim and Paul:
>> that seemed to be grep holding on to a no-arbitrary-limits dogma,
>> at the expense of its users, causing an absurd line-length issue,
>> which use of SEEK_DATA happens to avoid in some cases.
>>
>> The cp of sparse files from Jeff and Dave was more convincing;
>> but I still didn't see why little old tmpfs needed to be ahead
>> of the pack.
>>
>> But at LinuxCon/Plumbers in San Diego in August, a more convincing
>> case was made: I was hoping you would not ask, because I did not take
>> notes, and cannot pass on the details - was it rpm building on tmpfs?
>> I was convinced enough to promise support on tmpfs when support on
>> ext4 goes in.
> 
> Re the cp-vs-sparse-file case, the current FIEMAP-based code in GNU
> cp is ugly and complicated enough that until recently it harbored a
> hard-to-reproduce data-corrupting bug[*].  Now that SEEK_DATA/SEEK_HOLE
> support work will work also for tmpfs and ext4, we can plan to remove
> the FIEMAP-based code in favor of a simpler SEEK_DATA/SEEK_HOLE-based
> implementation.
How do we teach du(1) to aware of the real disk footprint with Btrfs
clone or OCFS2 reflinked files if we remove the FIEMAP-based code?

How about if we still keep it there, and introduce SEEK_DATA/SEEK_HOLE
code to the extent-scan module which is dedicated to deal with sparse files?

Thanks,
-Jeff
> 
> With the rise of virtualization, copying sparse images efficiently
> (probably searching, too) is becoming more and more important.
> 
> So, yes, GNU cp will soon use this feature.
> 
> [*] https://plus.google.com/u/0/114228401647637059102/posts/FDV3JEaYsKD
> --
> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>