[PATCH] Default to 1MiB alignment when possible (#618255)

[Brian C. Lane]

NOTE: This applies cleanly to parted-2.1 and parted-2.3


To better support 4k sector drives this changes the
linux_get_optimum_alignment() function to prefer aligning partitions to
DEFAULT_ALIGNMENT (1048576) if possible.

This also modifies the alignment test to take this change into account.
---
 include/parted/parted.h  |    2 ++
 libparted/arch/linux.c   |   29 ++++++++++++++++++++++-------
 libparted/device.c       |    2 +-
 tests/t9020-alignment.sh |    2 +-
 4 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/include/parted/parted.h b/include/parted/parted.h
index 14bd63e..714d1c6 100644
--- a/include/parted/parted.h
+++ b/include/parted/parted.h
@@ -19,6 +19,8 @@
 #ifndef PARTED_H_INCLUDED
 #define PARTED_H_INCLUDED
 
+#define DEFAULT_ALIGNMENT       1048576
+
 #ifdef __cplusplus
 extern "C" {
 #endif
diff --git a/libparted/arch/linux.c b/libparted/arch/linux.c
index b506db8..df18439 100644
--- a/libparted/arch/linux.c
+++ b/libparted/arch/linux.c
@@ -2591,13 +2591,28 @@ linux_get_optimum_alignment(const PedDevice *dev)
         if (!tp)
                 return NULL;
 
-        /* If optimal_io_size is 0 _and_ alignment_offset is 0 _and_
-           minimum_io_size is a power of 2 then go with the device.c default */
-        unsigned long minimum_io_size = blkid_topology_get_minimum_io_size(tp);
-        if (blkid_topology_get_optimal_io_size(tp) == 0 &&
-            blkid_topology_get_alignment_offset(tp) == 0 &&
-            (minimum_io_size & (minimum_io_size - 1)) == 0)
-                return NULL;
+        /* When DEFAULT_ALIGNMENT is divisible by the *_io_size or there
+         * are no *_io_size values use the DEFAULT_ALIGNMENT
+         * If one or the other will not divide evenly fall through to
+         * previous logic.
+         */
+        unsigned long optimal_io = blkid_topology_get_optimal_io_size(tp);
+        unsigned long minimum_io = blkid_topology_get_minimum_io_size(tp);
+        if (
+            (!optimal_io && !minimum_io) ||
+            ((optimal_io && (DEFAULT_ALIGNMENT % optimal_io) == 0) &&
+             (minimum_io && (DEFAULT_ALIGNMENT % minimum_io) == 0)    ) ||
+            (!minimum_io && optimal_io && (DEFAULT_ALIGNMENT % optimal_io) == 
0) ||
+            (!optimal_io && minimum_io && (DEFAULT_ALIGNMENT % minimum_io) == 
0)
+           ) {
+            /* DASD needs to use minimum alignment */
+            if (dev->type == PED_DEVICE_DASD)
+                return linux_get_minimum_alignment(dev);
+
+            return ped_alignment_new(
+                    blkid_topology_get_alignment_offset(tp) / dev->sector_size,
+                    DEFAULT_ALIGNMENT / dev->sector_size);
+        }
 
         /* If optimal_io_size is 0 and we don't meet the other criteria
            for using the device.c default, return the minimum alignment. */
diff --git a/libparted/device.c b/libparted/device.c
index 64da978..6149f0b 100644
--- a/libparted/device.c
+++ b/libparted/device.c
@@ -544,7 +544,7 @@ ped_device_get_optimum_alignment(const PedDevice *dev)
                 default:
                         /* Align to a grain of 1MiB (like vista / win7) */
                         align = ped_alignment_new(0,
-                                                  1048576 / dev->sector_size);
+                                                  DEFAULT_ALIGNMENT / 
dev->sector_size);
                 }
         }
 
diff --git a/tests/t9020-alignment.sh b/tests/t9020-alignment.sh
index 277fd47..83a5c15 100755
--- a/tests/t9020-alignment.sh
+++ b/tests/t9020-alignment.sh
@@ -36,7 +36,7 @@ grep '^#define USE_BLKID 1' "$CONFIG_HEADER" > /dev/null ||
 
 cat <<EOF > exp || framework_failure
 minimum: 7 8
-optimal: 7 64
+optimal: 7 2048
 partition alignment: 0 1
 EOF
 
-- 
1.7.3.2