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

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

On 05.07.22 09:45, Sascha Hauer wrote:
> On Thu, Jun 30, 2022 at 02:40:34PM +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:
>>
>>   devloop /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>
>> ---
>>  commands/Kconfig     | 13 ++++++++
>>  commands/Makefile    |  1 +
>>  commands/devlookup.c | 73 ++++++++++++++++++++++++++++++++++++++++++++
>>  3 files changed, 87 insertions(+)
>>  create mode 100644 commands/devlookup.c
>>
>> diff --git a/commands/Kconfig b/commands/Kconfig
>> index fb4dcefed8bf..5bab78fd1ce7 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 6c3a7a1dabcd..b43da1a80173 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..9599df7b10bc
>> --- /dev/null
>> +++ b/commands/devlookup.c
>> @@ -0,0 +1,73 @@
>> +// 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 (variable)
>> +		return setenv(variable, val);
>> +
>> +	if (!val)
>> +		return -errno;
>> +
>> +	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/"))
>> +		return COMMAND_ERROR_USAGE;
> 
> Should we skip the /dev/ part so that we can allow cdev names directly?
> Something like:
> 
> 	if (strstarts(devicefile, "/dev/"))
> 		devicefile += sizeof "/dev/" - 1;

Sounds good to me.

> 
> Sascha
> 
> 


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