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

[Paul Eggert]

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.  */
 
-- 
1.8.3.1