Re: [PATCH v2] diskfilter: use nodes in logical volume's segment as member device

[Daniel Kiper]

On Thu, Sep 09, 2021 at 09:02:29PM +0800, Michael Chang via Grub-devel wrote:
> 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 | 60 ++++++++++++++++++++++++++-----------
>  1 file changed, 43 insertions(+), 17 deletions(-)
>
> diff --git a/grub-core/disk/diskfilter.c b/grub-core/disk/diskfilter.c
> index 6eb2349a6..3d02d56ec 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 +333,51 @@ 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.  */

Again, please fix formatting of this comment if you are moving it [1].

> +           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;

Please call grub_error() here.

> +       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:

Please add a space before label.

> +

Please drop this empty line.

> +  while (list != NULL)
> +    {
> +      tmp = list;
> +      list = list->next;
> +      grub_free (tmp);
> +    }
> +
> +  return NULL;
>  }

Daniel

[1] https://www.gnu.org/software/grub/manual/grub-dev/grub-dev.html#Comments