[RFC PATCH 0/2] grub-probe: improve message when disk cannot be opened

[Antonio Ospite]

Hi,

right now when running grub-probe and the disk cannot be opened the
error message can be misleading, it always says "disk not found" but in
some case the disk may exist but the user has no permissions to open
it, see https://savannah.gnu.org/bugs/?42409

The message can be improved by propagating informations about the cause
of the failure from the bottom layers.

Please take a look at the patches in this series, I marked them RFC
because I am new to grub code and I am not sure that all the error paths
set a meaningful message, but I wanted some code to base the discussion
on.

Patch 1/2 aims to prevent overriding the error messages from the
disk->open() methods called in grub_disk_open().

Patch 2/2 exposes to the user the —now more informative— message from
grub_disk_open().

Before these changes I was getting this output when running grub-probe
with insufficient permissions:

  $ LANG=C ./grub-probe /
  ./grub-probe: warning: disk does not exist, so falling back to partition 
device /dev/sda1.
  ./grub-probe: warning: disk does not exist, so falling back to partition 
device /dev/sda1.
  ./grub-probe: warning: disk does not exist, so falling back to partition 
device /dev/sda1.
  ./grub-probe: error: disk `hostdisk//dev/sda1' not found.


After the patches the reason of the failure is clearer:

  $ LANG=C ./grub-probe /
  ./grub-probe: warning: cannot open `/dev/sda': Permission denied, so falling 
back to partition device /dev/sda1.
  ./grub-probe: warning: cannot open `/dev/sda': Permission denied, so falling 
back to partition device /dev/sda1.
  ./grub-probe: warning: cannot open `/dev/sda': Permission denied, so falling 
back to partition device /dev/sda1.
  ./grub-probe: error: cannot open `/dev/sda1': Permission denied.


As I said, this is the final effect I am aiming for but I am not 100%
sure my solution is complete.

Thanks,
   Antonio


Antonio Ospite (2):
  * grub-core/kern/disk.c: don't override grub_errmsg when
    grub_disk_open fails
  * util/getroot.c: improve error message when a disk cannot be opened

 grub-core/kern/disk.c |  3 +--
 util/getroot.c        | 15 +++++++++------
 2 files changed, 10 insertions(+), 8 deletions(-)

-- 
Antonio Ospite
http://ao2.it

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