[PATCH 0/1] libfdisk: allow to change an existing extended partition

[PATCH 0/1] libfdisk: allow to change an existing extended partition

[Pavel Butsykin]

The sfdisk utility does not allow us to change any extended partition type to
another extended type:
# sfdisk --list /dev/nbd0
Disk /dev/nbd0: 66 GiB, 70866960384 bytes, 138412032 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x006bf65f

Device      Boot   Start       End   Sectors  Size Id Type
/dev/nbd0p1 *       2048    999423    997376  487M 83 Linux
/dev/nbd0p2      1001470 138412031 137410562 65,5G  5 Extended

# sfdisk --part-type /dev/nbd0 2 0x85
Extended partition already exists.
lt-sfdisk: /dev/nbd0: partition 2: failed to set partition type

But why? As far as I understand, this is done in order to avoid more than one
extented partition on MBR disk (because MBR doesn't support more). But since
extended partition there are three types:
#define IS_EXTENDED(i) \
    ((i) == MBR_DOS_EXTENDED_PARTITION \
     || (i) == MBR_W95_EXTENDED_PARTITION \
     || (i) == MBR_LINUX_EXTENDED_PARTITION)

It would be nice to have the option to change the type of an existing extended
partition.

Pavel Butsykin (1):
  libfdisk: allow to change an existing extended partition

 libfdisk/src/dos.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

-- 
2.11.0

[PATCH 1/1] libfdisk: allow to change an existing extended partition

[Pavel Butsykin]

Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
---
 libfdisk/src/dos.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libfdisk/src/dos.c b/libfdisk/src/dos.c
index 39e42e3e6..8f54f7369 100644
--- a/libfdisk/src/dos.c
+++ b/libfdisk/src/dos.c
@@ -2025,7 +2025,7 @@ static int dos_set_partition(struct fdisk_context *cxt, size_t n,
 	orgtype = p->sys_ind;
 
 	if (pa->type) {
-		if (IS_EXTENDED(pa->type->code) && l->ext_offset) {
+		if (IS_EXTENDED(pa->type->code) && l->ext_offset && l->ext_index != n) {
 			fdisk_warnx(cxt, _("Extended partition already exists."));
 			return -EINVAL;
 		}
-- 
2.11.0

Re: [PATCH 1/1] libfdisk: allow to change an existing extended partition

[Karel Zak]

On Tue, Apr 18, 2017 at 06:59:18PM +0300, Pavel Butsykin wrote:
>  libfdisk/src/dos.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Applied, thanks!

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com