Re: [Bug-tar] [PATCH] Remove nonportable check for files containing only zeroes

[Mark H Weaver]

Hi Andreas,

Andreas Dilger <address@hidden> writes:

> On Jan 20, 2018, at 5:06 PM, Mark H Weaver <address@hidden> wrote:
>> Yes, on Btrfs I reliably see (st_blocks == 0) on a recently written,
>> mostly sparse file with size > 8G, using linux-libre-4.14.14.  More
>> specifically, the "storing sparse files > 8G" test in tar's test suite
>> reliably fails on my system:
>> 
>>  140: storing sparse files > 8G                       FAILED (sparse03.at:29)
>
> I'd consider this a bug in Btrfs.

On what basis?  Can you formulate a precise rule regarding 'st_blocks'
that is worth defending, that would enable this optimization, and that
Btrfs is violating here?

> As mentioned previously, we had the same problem with ext4 (twice) and
> Lustre, and in both cases fixed this by adding in the (dirty page
> cache pages/512) if the current block count is zero:

Would you like to propose a fix to the Btrfs developers?

     Mark