Re: [Bug-tar] --sparse is broken on filesystems where small files may have zero blocks

[Andrew J. Schorr]

Hi Paul,

On Mon, Oct 28, 2013 at 09:19:58PM -0700, Paul Eggert wrote:
> Thanks for the bug report.  I pushed the following patch to paxutils
> and it should propagate into GNU tar in the next release.
> 
> >From 63493234ec38ad606a5f726bc82e4fe5d8661cab Mon Sep 17 00:00:00 2001
> From: Paul Eggert <address@hidden>
> Date: Mon, 28 Oct 2013 21:16:53 -0700
> Subject: [PATCH] paxutils: support --sparse with tiny files on Netapp filers
> 
> * lib/system.h (ST_IS_SPARSE): Port to NFS + Netapp filers,
> where a tiny file can have zero blocks but nonzero size.
> Problem reported by Andrew J. Schorr in
> <http://lists.gnu.org/archive/html/bug-tar/2013-10/msg00030.html>.
> ---
>  lib/system.h | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/system.h b/lib/system.h
> index ef46267..e7f531c 100644
> --- a/lib/system.h
> +++ b/lib/system.h
> @@ -389,9 +389,16 @@ extern int errno;
>  # define ST_NBLOCKSIZE 512
>  #endif
>  
> +/* Network Appliance file systems store small files directly in the
> +   inode if st_size <= 64; in this case the number of blocks can be
> +   zero.  Perhaps other file systems have similar problems; so,
> +   somewhat arbitrarily, do not consider a file to be sparse if
> +   it has no blocks but st_size < ST_NBLOCKSIZE.  */
>  #define ST_IS_SPARSE(st)                                  \
>    (ST_NBLOCKS (st)                                        \
> -    < ((st).st_size / ST_NBLOCKSIZE + ((st).st_size % ST_NBLOCKSIZE != 0)))
> +   < ((st).st_size / ST_NBLOCKSIZE                     \
> +      + ((st).st_size % ST_NBLOCKSIZE != 0             \
> +      && (st).st_size / ST_NBLOCKSIZE != 0)))
>  
>  /* Declare standard functions.  */

Thanks for the patch, but I don't think that fixes the problem in
sparse.c:sparse_scan_file where it says

   if (ST_NBLOCKS (st->stat) == 0)
     offset = st->stat.st_size;
   else
     ...

Regards,
Andy