[gnome-disk-utility] Use fallocate(2) rather than posix_fallocate(3)

[David Zeuthen <davidz src gnome org>]

commit d96d30229782682b1aecf697ec9ba573b7ea6aca
Author: David Zeuthen <zeuthen gmail com>
Date:   Fri May 31 19:57:39 2013 -0700

    Use fallocate(2) rather than posix_fallocate(3)
    
    The latter simulates fallocate(2) if the underlying FS doesn't support
    it. This is unwanted and slow, especially on e.g. CIFS or NFS.
    
    Signed-off-by: David Zeuthen <zeuthen gmail com>

 configure.ac                         |   20 +++++++++++++++++
 src/disks/gducreatediskimagedialog.c |   40 +++++++++++++++++++++++-----------
 2 files changed, 47 insertions(+), 13 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 5f669a1..e38fcf0 100644
--- a/configure.ac
+++ b/configure.ac
@@ -77,6 +77,26 @@ CC_CHECK_CFLAGS_APPEND([                          \
         -fno-strict-aliasing                      \
 ])
 
+AC_MSG_CHECKING([for valid fallocate() function])
+AC_LINK_IFELSE([
+AC_LANG_PROGRAM([[
+#include <unistd.h>
+#include <sys/types.h>
+#include <linux/falloc.h>
+#include <fcntl.h>
+]],[[
+   long ret;
+
+   ret = fallocate(0, FALLOC_FL_KEEP_SIZE, 0xfffffffful, 0xfffffffful);
+
+   if (ret != 0) {
+      return 1;
+   }
+   ]])],[
+AC_MSG_RESULT([yes])
+AC_DEFINE(HAVE_FALLOCATE,1,[Have valid fallocate() function])],[
+AC_MSG_RESULT([no])])
+
 # ***************************
 # Check for required packages
 # ***************************
diff --git a/src/disks/gducreatediskimagedialog.c b/src/disks/gducreatediskimagedialog.c
index 2817a89..305707a 100644
--- a/src/disks/gducreatediskimagedialog.c
+++ b/src/disks/gducreatediskimagedialog.c
@@ -9,6 +9,9 @@
 
 #include "config.h"
 
+#define _GNU_SOURCE
+#include <fcntl.h>
+
 #include <glib/gi18n.h>
 #include <gio/gunixfdlist.h>
 #include <gio/gunixinputstream.h>
@@ -727,36 +730,47 @@ copy_thread_func (gpointer user_data)
       goto out;
     }
 
-  /* Allocate space at once to ensure blocks are laid out contigously,
-   * see http://lwn.net/Articles/226710/
+  /* If supported, allocate space at once to ensure blocks are laid
+   * out contigously, see http://lwn.net/Articles/226710/
    */
+#ifdef HAVE_FALLOCATE
   if (G_IS_FILE_DESCRIPTOR_BASED (data->output_file_stream))
     {
       gint output_fd = g_file_descriptor_based_get_fd (G_FILE_DESCRIPTOR_BASED (data->output_file_stream));
       gint rc;
 
-      /* With some filesystems drivers - for example ntfs-3g - posix_fallocate(3) may take a
-       * loong time since it may be implemented as writing zeroes to the file.
-       */
       g_mutex_lock (&data->copy_lock);
       data->allocating_file = TRUE;
       g_mutex_unlock (&data->copy_lock);
       g_idle_add (on_update_job, dialog_data_ref (data));
 
-      rc = posix_fallocate (output_fd, (off_t) 0, (off_t) block_device_size);
+      rc = fallocate (output_fd,
+                      0, /* mode */
+                      (off_t) 0,
+                      (off_t) block_device_size);
+
+      if (rc != 0)
+        {
+          if (errno == ENOSYS || errno == EOPNOTSUPP)
+            {
+              /* If the kernel or filesystem does not support it, too
+               * bad. Just continue.
+               */
+            }
+          else
+            {
+              error = g_error_new (G_IO_ERROR, g_io_error_from_errno (errno), "%s", strerror (errno));
+              g_prefix_error (&error, _("Error allocating space for disk image file: "));
+              goto out;
+            }
+        }
 
       g_mutex_lock (&data->copy_lock);
       data->allocating_file = FALSE;
       g_mutex_unlock (&data->copy_lock);
       g_idle_add (on_update_job, dialog_data_ref (data));
-
-      if (rc != 0)
-        {
-          error = g_error_new (G_IO_ERROR, g_io_error_from_errno (rc), "%s", strerror (rc));
-          g_prefix_error (&error, _("Error allocating space for disk image file: "));
-          goto out;
-        }
     }
+#endif
 
   page_size = sysconf (_SC_PAGESIZE);
   buffer_unaligned = g_new0 (guchar, buffer_size + page_size);