[PATCH v2 2/3] commands: implement devlookup to find device behind device file

[Sascha Hauer]

On Tue, Jul 05, 2022 at 02:04:36PM +0200, Ahmad Fatoum wrote:
> On 05.07.22 13:59, Sascha Hauer wrote:
> > On Tue, Jul 05, 2022 at 01:55:37PM +0200, Ahmad Fatoum wrote:
> >> 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 at pengutronix.de>
> >> ---
> >> v1 -> v2:
> >>   - fix typo in commit message (Michael)
> >>   - accept cdev without /dev/ prefix (Sascha)
> >>   - early exit on cdev without dev, e.g. /dev/zero
> >> ---
> >>  commands/Kconfig     | 13 ++++++++
> >>  commands/Makefile    |  1 +
> >>  commands/devlookup.c | 78 ++++++++++++++++++++++++++++++++++++++++++++
> >>  3 files changed, 92 insertions(+)
> >>  create mode 100644 commands/devlookup.c
> >>
> >> diff --git a/commands/Kconfig b/commands/Kconfig
> >> index c5505321cfd9..037b41155695 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"
> >> diff --git a/commands/Makefile b/commands/Makefile
> >> index b3b7bafe6b64..0aae8893d696 100644
> >> --- a/commands/Makefile
> >> +++ b/commands/Makefile
> >> @@ -110,6 +110,7 @@ obj-$(CONFIG_CMD_DETECT)	+= detect.o
> >>  obj-$(CONFIG_CMD_BOOT)		+= boot.o
> >>  obj-$(CONFIG_CMD_DEVINFO)	+= devinfo.o
> >>  obj-$(CONFIG_CMD_DEVUNBIND)	+= devunbind.o
> >> +obj-$(CONFIG_CMD_DEVLOOKUP)	+= devlookup.o
> >>  obj-$(CONFIG_CMD_DRVINFO)	+= drvinfo.o
> >>  obj-$(CONFIG_CMD_READF)		+= readf.o
> >>  obj-$(CONFIG_CMD_MENUTREE)	+= menutree.o
> >> diff --git a/commands/devlookup.c b/commands/devlookup.c
> >> new file mode 100644
> >> index 000000000000..c361d5b58860
> >> --- /dev/null
> >> +++ b/commands/devlookup.c
> >> @@ -0,0 +1,78 @@
> >> +// SPDX-License-Identifier: GPL-2.0-only
> >> +
> >> +#include <common.h>
> >> +#include <command.h>
> >> +#include <fs.h>
> >> +#include <getopt.h>
> >> +#include <malloc.h>
> >> +#include <linux/stat.h>
> >> +#include <linux/ctype.h>
> >> +#include <environment.h>
> >> +
> >> +static int report(const char *variable, const char *val)
> >> +{
> >> +	if (!val)
> >> +		return -(errno ?: EINVAL);
> >> +
> >> +	if (variable)
> >> +		return setenv(variable, val);
> >> +
> >> +	printf("%s\n", val);
> >> +	return 0;
> >> +}
> >> +
> >> +static int do_devlookup(int argc, char *argv[])
> >> +{
> >> +	const char *variable = NULL, *devicefile, *paramname;
> >> +	struct cdev *cdev;
> >> +	int opt;
> >> +
> >> +	while ((opt = getopt(argc, argv, "v:")) > 0) {
> >> +		switch(opt) {
> >> +		case 'v':
> >> +			variable = optarg;
> >> +			break;
> >> +		}
> >> +	}
> >> +
> >> +	if (argc - optind == 0 || argc - optind > 2)
> >> +		return COMMAND_ERROR_USAGE;
> >> +
> >> +	devicefile = argv[optind];
> >> +	paramname  = argv[optind+1];
> >> +
> >> +	if (strstarts(devicefile, "/dev/"))
> >> +		devicefile += sizeof("/dev/") - 1;
> > 
> > Forgot to mention: We have devpath_to_name() which does exactly that.
> > Also I merged your last series with that change, so unless you have
> > made other changes we should be fine.
> 
> Yes, I added a check below for deviceless cdevs, which otherwise
> would crash on devlookup /dev/full
> 
> Do you need me to create a v3 or will you fix this up?

I fixed it up.

Sascha

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