fiemap copy: add extent-scan.[ch], avoid a double-free and reorganize

Changes:
========
1. fix write_zeros() per Jim's comments.
2. remove char const *fname from struct extent_scan.
3. change the signature of open_extent_scan() from
"void open_extent_scan(struct extent_scan **scan)" to
"void open_extent_scan(struct extent_scan *scan)" to avoid having
to malloc the extent_scan variable; instead save it on the stack.
4. move close_extent_scan() from a function defined in extent-scan.c
to extent-scan.h as a macro definition, but it does nothing for now,
since initial extent scan defined at stack.
5. add a macro "free_extents_info()" defined at extent-scan.h to
release the memory allocated to extent info which should be called
combine with get_extents_info(), it just one line, so IMHO, define
it as macro should be ok.

* src/extent-scan.c: New file; functions to read "extents".
* src/extent-scan.h: Header file of extent-scan.c.
* src/Makefile.am: Reference it and link it to copy_source.
* src/copy.c: Use the new functions and avoid double-free.

1 files changed, 113 insertions, 0 deletions

diff --git a/src/extent-scan.c b/src/extent-scan.c
new file mode 100644
index 000000000..f371b8718
--- /dev/null
+++ b/src/extent-scan.c
@@ -0,0 +1,113 @@
+/* extent-scan.c -- core functions for scanning extents
+   Copyright (C) 2010 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+   Written by Jie Liu (jeff.liu@oracle.com).  */
+
+#include <config.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <sys/ioctl.h>
+#include <assert.h>
+
+#include "system.h"
+#include "extent-scan.h"
+#include "error.h"
+#include "quote.h"
+
+#ifndef HAVE_FIEMAP
+# include "fiemap.h"
+#endif
+
+/* Allocate space for struct extent_scan, initialize the entries if
+   necessary and return it as the input argument of get_extents_info().  */
+extern void
+open_extent_scan (int src_fd, struct extent_scan *scan)
+{
+  scan->fd = src_fd;
+  scan->ei_count = 0;
+  scan->scan_start = 0;
+  scan->initial_scan_failed = false;
+  scan->hit_last_extent = false;
+}
+
+#ifdef __linux__
+# ifndef FS_IOC_FIEMAP
+#  define FS_IOC_FIEMAP _IOWR ('f', 11, struct fiemap)
+# endif
+/* Call ioctl(2) with FS_IOC_FIEMAP (available in linux 2.6.27) to
+   obtain a map of file extents excluding holes.  */
+extern bool
+get_extents_info (struct extent_scan *scan)
+{
+  union { struct fiemap f; char c[4096]; } fiemap_buf;
+  struct fiemap *fiemap = &fiemap_buf.f;
+  struct fiemap_extent *fm_extents = &fiemap->fm_extents[0];
+  enum { count = (sizeof fiemap_buf - sizeof *fiemap) / sizeof *fm_extents };
+  verify (count != 0);
+  unsigned int i;
+
+  /* This is required at least to initialize fiemap->fm_start,
+     but also serves (in mid 2010) to appease valgrind, which
+     appears not to know the semantics of the FIEMAP ioctl. */
+  memset (&fiemap_buf, 0, sizeof fiemap_buf);
+
+  fiemap->fm_start = scan->scan_start;
+  fiemap->fm_flags = FIEMAP_FLAG_SYNC;
+  fiemap->fm_extent_count = count;
+  fiemap->fm_length = FIEMAP_MAX_OFFSET - scan->scan_start;
+
+  /* Fall back to the standard copy if call ioctl(2) failed for the
+     the first time.  */
+  if (ioctl (scan->fd, FS_IOC_FIEMAP, fiemap) < 0)
+    {
+      if (scan->scan_start == 0)
+        scan->initial_scan_failed = true;
+      return false;
+    }
+
+  /* If 0 extents are returned, then more get_extent_table() are not needed.  */
+  if (fiemap->fm_mapped_extents == 0)
+    {
+      scan->hit_last_extent = true;
+      return false;
+    }
+
+  scan->ei_count = fiemap->fm_mapped_extents;
+  scan->ext_info = xnmalloc (scan->ei_count, sizeof (struct extent_info));
+
+  for (i = 0; i < scan->ei_count; i++)
+    {
+      assert (fm_extents[i].fe_logical <= OFF_T_MAX);
+
+      scan->ext_info[i].ext_logical = fm_extents[i].fe_logical;
+      scan->ext_info[i].ext_length = fm_extents[i].fe_length;
+      scan->ext_info[i].ext_flags = fm_extents[i].fe_flags;
+    }
+
+  i--;
+  if (scan->ext_info[i].ext_flags & FIEMAP_EXTENT_LAST)
+    {
+      scan->hit_last_extent = true;
+      return true;
+    }
+
+  scan->scan_start = fm_extents[i].fe_logical + fm_extents[i].fe_length;
+
+  return true;
+}
+#else
+extern bool get_extents_info (ignored) { errno = ENOTSUP; return false; }
+#endif