[PATCH v3] diskfilter: use nodes in logical volume's segment as member device

[Michael Chang]

Currently the grub_diskfilter_memberlist function returns all physical
volumes added to a volume group to which a logical volume (LV) belongs.
However this is suboptimal as it doesn't fit the intended behavior of
returning underlying devices that make up the LV. To give a clear
picture, the result should be identical to running commands below to
display the logical volumes with underlying physical volumes in use.

  localhost:~ # lvs -o lv_name,vg_name,devices /dev/system/root
    LV   VG     Devices
    root system /dev/vda2(512)

  localhost:~ # lvdisplay --maps /dev/system/root
    --- Logical volume ---
      ...
    --- Segments ---
    Logical extents 0 to 4604:
      Type                linear
      Physical volume     /dev/vda2
      Physical extents    512 to 5116

As shown above, we can know system-root lv uses only /dev/vda2 to
allocate it's extents, or we can say that /dev/vda2 is the member device
comprising the system-root lv.

It is important to be precise on the member devices, because that helps
to avoid pulling in excessive dependency. Let's use an example to
demonstrate why it is needed.

  localhost:~ # findmnt /
  TARGET SOURCE                  FSTYPE OPTIONS
  /      /dev/mapper/system-root ext4   rw,relatime

  localhost:~ # pvs
    PV               VG     Fmt  Attr PSize    PFree
    /dev/mapper/data system lvm2 a--  1020.00m    0
    /dev/vda2        system lvm2 a--    19.99g    0

  localhost:~ # cryptsetup status /dev/mapper/data
  /dev/mapper/data is active and is in use.
    type:    LUKS1
    cipher:  aes-xts-plain64
    keysize: 512 bits
    key location: dm-crypt
    device:  /dev/vdb
    sector size:  512
    offset:  4096 sectors
    size:    2093056 sectors
    mode:    read/write

  localhost:~ # vgs
    VG     #PV #LV #SN Attr   VSize  VFree
    system   2   3   0 wz--n- 20.98g    0

  localhost:~ # lvs -o lv_name,vg_name,devices
    LV   VG     Devices
    data system /dev/mapper/data(0)
    root system /dev/vda2(512)
    swap system /dev/vda2(0)

We can learn from above that /dev/mapper/data is an encrypted volume and
also gets assigned to volume group 'system' as one of it's physical
volumes. And also it is not used by root device,
/dev/mapper/system-root, for allocating extents, so it shouldn't be
taking part in the process of setting up grub to access root device.

However running grub-install reports error as volume group 'system'
contains encrypted volume.

  error: attempt to install to encrypted disk without cryptodisk
  enabled. Set `GRUB_ENABLE_CRYPTODISK=y' in file `/etc/default/grub'.

Certainly we can enable GRUB_ENABLE_CRYPTODISK=y and move on, but that
is not always acceptable since the server may need to be booted
unattended. Additionally, typing passphase for every system startup can
be a big hassle of which most users would like to avoid.

This patch solves the problem by returning exact physical volume,
/dev/vda2, rightly used by system-root from the example above, thus
grub-install will not error out because the excessive encrypted device
to boot the root device is not configured.

Signed-off-by: Michael Chang <mchang@suse.com>
Tested-by: Olav Reinert <seroton10@gmail.com>
---
 grub-core/disk/diskfilter.c | 61 ++++++++++++++++++++++++++-----------
 1 file changed, 44 insertions(+), 17 deletions(-)

diff --git a/grub-core/disk/diskfilter.c b/grub-core/disk/diskfilter.c
index 032011566..1eafc2dc3 100644
--- a/grub-core/disk/diskfilter.c
+++ b/grub-core/disk/diskfilter.c
@@ -300,6 +300,8 @@ grub_diskfilter_memberlist (grub_disk_t disk)
   grub_disk_dev_t p;
   struct grub_diskfilter_vg *vg;
   struct grub_diskfilter_lv *lv2 = NULL;
+  struct grub_diskfilter_segment *seg;
+  unsigned int i, j;
 
   if (!lv->vg->pvs)
     return NULL;
@@ -331,27 +333,52 @@ grub_diskfilter_memberlist (grub_disk_t disk)
            }
     }
 
-  for (pv = lv->vg->pvs; pv; pv = pv->next)
-    {
-      if (!pv->disk)
+  for (i = 0, seg = lv->segments; i < lv->segment_count; i++, seg++)
+    for (j = 0; j < seg->node_count; ++j)
+      if (seg->nodes[j].pv != NULL)
        {
-         /* TRANSLATORS: This message kicks in during the detection of
-            which modules needs to be included in core image. This happens
-            in the case of degraded RAID and means that autodetection may
-            fail to include some of modules. It's an installation time
-            message, not runtime message.  */
-         grub_util_warn (_("Couldn't find physical volume `%s'."
-                           " Some modules may be missing from core image."),
-                         pv->name);
-         continue;
+         pv = seg->nodes[j].pv;
+
+         if (!pv->disk)
+           {
+             /*
+              * TRANSLATORS: This message kicks in during the detection of
+              * which modules needs to be included in core image. This happens
+              * in the case of degraded RAID and means that autodetection may
+              * fail to include some of modules. It's an installation time
+              * message, not runtime message.
+              */
+             grub_util_warn (_("Couldn't find physical volume `%s'."
+                               " Some modules may be missing from core 
image."),
+                             pv->name);
+             continue;
+           }
+
+         for (tmp = list; tmp != NULL; tmp = tmp->next)
+           if (!grub_strcmp (tmp->disk->name, pv->disk->name))
+             break;
+         if (tmp != NULL)
+           continue;
+
+         tmp = grub_malloc (sizeof (*tmp));
+         if (!tmp)
+           goto fail;
+         tmp->disk = pv->disk;
+         tmp->next = list;
+         list = tmp;
        }
-      tmp = grub_malloc (sizeof (*tmp));
-      tmp->disk = pv->disk;
-      tmp->next = list;
-      list = tmp;
-    }
 
   return list;
+
+ fail:
+  while (list != NULL)
+    {
+      tmp = list;
+      list = list->next;
+      grub_free (tmp);
+    }
+
+  return NULL;
 }
 
 void
-- 
2.31.1