commands: implement devlookup to find device behind device file

For OF-enabled platforms with aliases, device file naming is pretty much
solved: If there is mmc2 = &something, then we have a mmc2 device and
a /dev/mmc2 device file. For other platforms like x86, EFI-provided
devices are harder to get ahold of. Add a command to make this
straight-forward to do in scripts. The main use of this is probably to
access parameters like nt_signature or guid:

  devlookup /dev/disk0 guid

This would print to console, but we have no output capture yet, so add
an optional -v VARIABLE parameter as well to allow easy use from
scripts.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.barebox.org/20220630124035.4019644-2-a.fatoum@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 13 insertions, 0 deletions

diff --git a/commands/Kconfig b/commands/Kconfig
index 86e4714849..69d76a9c80 100644
--- a/commands/Kconfig
+++ b/commands/Kconfig
@@ -75,6 +75,19 @@ config CMD_DEVINFO
 	  If called with a device path being the argument, devinfo shows more
 	  default information about this device and its parameters.
 
+config CMD_DEVLOOKUP
+	tristate
+	prompt "devlookup"
+	help
+	  Look up device behind device file and its parameters
+
+	  devlookup [-v VAR] /dev/DEVICE [parameter]
+
+          Detects the device behind a device file and outputs it,
+          unless a second argument is given. In that case the device
+          parameter with that name is looked up. Specifying -v VARIABLE
+          will write output to VARIABLE instead of printing it.
+
 config CMD_DEVUNBIND
 	tristate
 	prompt "devunbind"