Re: [PATCH] of: Respect CONFIG_CMDLINE{,_EXTENED,_FORCE) with no chosen node

[Palmer Dabbelt <palmer@sifive.com>]

On Sun, 18 Mar 2018 05:51:50 PDT (-0700), robh@kernel.org wrote:
> On Wed, Mar 14, 2018 at 09:31:05AM -0700, Palmer Dabbelt wrote:
>> Systems that boot without a chosen node in the device tree should still
>> respect the command lines that are built into the kernel.  This patch
>> avoids bailing out of the command line argument parsing code when there
>> is no chosen node in the device tree.  This is necessary to boot
>> straight to a root file system (ie, without an initramfs)
>>
>> The intent here is that the only functional change is to copy
>> CONFIG_CMDLINE into data if both of them are valid (ie, CONFIG_CMDLINE
>> is defined and data is non-null) on systems where there is no chosen
>> device tree node.  I don't actually know what the return values do so I
>> just preserved them.
>>
>> Thanks to Trung and Moritz for finding the bug during our ELC hackathon
>> (and providing the first fix), and Michal for suggesting this fix (which
>> is cleaner than what I was doing).  I've given this very minimal
>> testing: it fixes the RISC-V bug (in conjunction with a patch to move
>> from COMMANDLINE_OVERRIDE to COMMANDLINE_FORCE), still works on systems
>> with and without the chosen node, and builds on ARM64.
>>
>> CC: Michael J Clark <mjc@sifive.com>
>> CC: Trung Tran <trung.tran@ettus.com>
>> CC: Moritz Fischer <mdf@kernel.org>
>> Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
>> ---
>>  drivers/of/fdt.c | 14 ++++++++++++--
>>  1 file changed, 12 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
>> index 84aa9d676375..60241b1cb024 100644
>> --- a/drivers/of/fdt.c
>> +++ b/drivers/of/fdt.c
>> @@ -1084,9 +1084,12 @@ int __init early_init_dt_scan_chosen(unsigned long node, const char *uname,
>>
>>  	pr_debug("search \"chosen\", depth: %d, uname: %s\n", depth, uname);
>>
>> -	if (depth != 1 || !data ||
>> +	if (!data)
>> +		goto no_data;
>
> Just "return 0" here.
>
>> +
>> +	if (depth != 1 ||
>>  	    (strcmp(uname, "chosen") != 0 && strcmp(uname, "chosen@0") != 0))
>> -		return 0;
>> +		goto no_chosen;
>>
>>  	early_init_dt_check_for_initrd(node);
>>
>> @@ -1117,6 +1120,13 @@ int __init early_init_dt_scan_chosen(unsigned long node, const char *uname,
>>
>>  	/* break now */
>>  	return 1;
>> +
>> +no_chosen:
>> +#ifdef CONFIG_CMDLINE
>> +	strlcpy(data, CONFIG_CMDLINE, COMMAND_LINE_SIZE);
>
> Best case, this is going to needlessly copy the string on every single
> node that is not /chosen.
>
> Worst case, I think this changes behavior. For example, first you copy
> CONFIG_CMDLINE into data, then on a later iteration, you strlcat
> CONFIG_CMDLINE into data if CONFIG_CMDLINE_EXTEND is enable. There could
> also be some unintended behavior if data has a string to start with.

Ah, sorry, I guess I wasn't paying attention -- I assumed this was only called
for the relevant node (like the rest of the device tree stuff), and that chosel
was just somewhere inside it.  

> I'd really like to see this function re-written to just find the /chosen
> node and then handle each property one by one. The iterating approach is
> silly. I assume it predates libfdt and we didn't have nice functions to
> find nodes by path (or any other way).
>
> I'm working on a patch to re-structure this function. Will send it out
> in the next day.
>
>> +#endif
>> +no_data:
>> +	return 0;
>>  }
>>
>>  #ifdef CONFIG_HAVE_MEMBLOCK
>> --
>> 2.16.1

Thanks.  Do you mind CCing me on it?  Then I'll figure out a way to make sure
our command lines still work.