s3: prefer posix_fallocate for doing "strict allocate"

posix_fallocate is more efficient than manual zero'ing the file. When
preallocation in kernel space is supported it's extremely fast. Support for
preallocation at fs layer via posix_fallocate and fallocate at kernel site
can be found in Linux kernel 2.6.23/glibc 2.10 with ext4, XFS and OCFS2. Other
systems that I know of which support fast preallocation in kernel space are
AIX 6.1 with JFS2 and recent Solaris versions with ZFS maybe UFS2, too.

People who have a system with preallocation in kernel space might want to set
"strict allocate = yes". This reduces file fragentation and it's also safer for
setups with quota being turned on.

As of today most systems still don't have preallocation in kernel space, and
that's why "strict allocate = no" will stay the default for now.

1 files changed, 14 insertions, 0 deletions

diff --git a/source3/lib/system.c b/source3/lib/system.c
index 86802d0c8d..b18358d8b2 100644
--- a/source3/lib/system.c
+++ b/source3/lib/system.c
@@ -610,6 +610,20 @@ int sys_lstat(const char *fname,SMB_STRUCT_STAT *sbuf,
 }
 
 /*******************************************************************
+ An posix_fallocate() wrapper that will deal with 64 bit filesizes.
+********************************************************************/
+#if defined(HAVE_POSIX_FALLOCATE64) || defined(HAVE_POSIX_FALLOCATE)
+int sys_posix_fallocate(int fd, SMB_OFF_T offset, SMB_OFF_T len)
+{
+#if defined(HAVE_EXPLICIT_LARGEFILE_SUPPORT) && defined(HAVE_OFF64_T) && defined(HAVE_POSIX_FALLOCATE64)
+	return posix_fallocate64(fd, offset, len);
+#else
+	return posix_fallocate(fd, offset, len);
+#endif
+}
+#endif
+
+/*******************************************************************
  An ftruncate() wrapper that will deal with 64 bit filesizes.
 ********************************************************************/