libparted: handle logical partitions starting immediately after the EBR

_blkpg_add_partition() set the length of the extended partition
to 2 sectors to allow LILO to be installed there, beacuse the
linux kernel does this.  If a logical partition used that second
sector, adding it would fail beacuse of the overlap.  Now
_blkpg_add_partition() will limit the length to only the first
sector if the second is used by a logical partition.

Previously parted did create the partition table, and after a
reboot, the kernel would recognize the table, and happily create
the extended partition as 2 sectors long, thus overlapping the
logical partition, but when parted tried to recreate the same
table with BLKPG, the kernel rightly rejected it.

3 files changed, 27 insertions, 14 deletions

diff --git a/NEWS b/NEWS
index a27200b..716e477 100644
--- a/NEWS
+++ b/NEWS
@@ -4,6 +4,14 @@ GNU parted NEWS                                    -*- outline -*-
 
 ** Bug Fixes
 
+  libparted: handle logical partitions starting immediately after
+  the EBR.  Creating a logical partition one sector after the EBR
+  used to cause parted to complain that it could not inform the
+  kernel of the changes, but after a reboot, everything was fine.
+  Parted will now correctly inform the kernel of the changes, but
+  only set the length of the extended partition to 1 sector instead
+  of two, which would cause it to overlap the logical partition.
+
   parted: fix EOF and ctrl-c handling.  parted used to refuse to exit
   in response to ctrl-c and would get stuck in an infinite loop
   prompting for more input when it reached EOF on stdin.
diff --git a/libparted/arch/linux.c b/libparted/arch/linux.c
index 2bb8774..05794d9 100644
--- a/libparted/arch/linux.c
+++ b/libparted/arch/linux.c
@@ -2473,8 +2473,21 @@ _blkpg_add_partition (PedDisk* disk, const PedPartition *part)
         memset (&linux_part, 0, sizeof (linux_part));
         linux_part.start = part->geom.start * disk->dev->sector_size;
         /* see fs/partitions/msdos.c:msdos_partition(): "leave room for LILO" */
-        if (part->type & PED_PARTITION_EXTENDED)
-                linux_part.length = part->geom.length == 1 ? 512 : 1024;
+        if (part->type & PED_PARTITION_EXTENDED) {
+                linux_part.length = 1;
+                if (disk->dev->sector_size == 512) {
+                        if (linux_part.length == 1)
+                                linux_part.length = 2;
+                        PedPartition *walk;
+                        /* if the second sector is claimed by a logical partition,
+                           then there's just no room for lilo, so don't try to use it */
+                        for (walk = part->part_list; walk; walk = walk->next) {
+                                if (walk->geom.start == part->geom.start+1)
+                                        linux_part.length = 1;
+                        }
+                }
+                linux_part.length *= disk->dev->sector_size;
+        }
         else
                 linux_part.length = part->geom.length * disk->dev->sector_size;
         linux_part.pno = part->num;
diff --git a/tests/t2310-dos-extended-2-sector-min-offset.sh b/tests/t2310-dos-extended-2-sector-min-offset.sh
index fe356dd..f74cba5 100644
--- a/tests/t2310-dos-extended-2-sector-min-offset.sh
+++ b/tests/t2310-dos-extended-2-sector-min-offset.sh
@@ -1,8 +1,6 @@
 #!/bin/sh
-# Ensure that parted leaves at least 2 sectors between the beginning
+# Ensure that parted allows a single sector between the beginning
 # of an extended partition and the first logical partition.
-# Before parted-2.3, it could be made to leave just one, and that
-# would cause trouble with the Linux kernel.
 
 # Copyright (C) 2010-2013 Free Software Foundation, Inc.
 
@@ -35,7 +33,7 @@ cat <<EOF > exp || framework_failure
 BYT;
 $scsi_dev:2048s:scsi:512:512:msdos:Linux scsi_debug:;
 1:64s:128s:65s:::lba;
-5:66s:128s:63s:::;
+5:65s:128s:64s:::;
 EOF
 
 cat <<EOF > err.exp || framework_failure
@@ -48,15 +46,9 @@ parted --align=min -s $scsi_dev mkpart extended 64s 128s> out 2>&1 || fail=1
 parted -m -s $scsi_dev u s print
 compare /dev/null out || fail=1
 
-# Provoke a failure by trying to create a partition that starts just
+# Trying to create a partition that starts just
 # one sector after the start of the extended partition.
-parted --align=min -s $scsi_dev mkpart logical 65s 128s > err 2>&1 && fail=1
-compare err.exp err || fail=1
-
-# The above failed, but created the partition nonetheless.  Remove it.
-parted -s $scsi_dev rm 5 || fail=1
-
-parted --align=min -s $scsi_dev mkpart logical 66s 128s > out 2>&1 || fail=1
+parted --align=min -s $scsi_dev mkpart logical 65s 128s > out 2>&1 || fail=1
 compare /dev/null out || fail=1
 
 parted -m -s $scsi_dev u s print > out 2>&1