of: Respect CONFIG_CMDLINE{, _EXTENED, _FORCE) with no chosen node

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(-)

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. 

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
> 
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> On 18/03/2018, at 5:51 AM, Rob Herring <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. 
> 
> 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).

Thanks very much for the feedback.

I think we had the right intent, which was to fix the issue in the generic device tree code rather than add a arch specific hack. Previously we had code in arch/riscv/kernel/setup.c which would copy the built-in command line but this clashed with the architecture neutral code, which resulted in appending the compiled-in command twice if the chosen node was present in device-tree. I’m adding Wes to the ‘cc as he has recently changed the HiFive Unleased device-tree to include an empty chosen node which is another workaround for the issue.

We weren’t aware that this code was called in a loop for each device-tree node. I guess one possibility is to hoist the CONFIG_CMDLINE code out of early_init_dt_scan_chosen into early_init_dt_scan and have early_init_dt_scan_chosen append bootargs or optionally ignore it if CONFIG_CMDLINE_OVERRIDE is set.

> I'm working on a patch to re-structure this function. Will send it out 
> in the next day.

Thanks!

It seems logical that the architecture neutral code should set the compiled in command-line if CONFIG_CMDLINE_OVERRIDE is set, whether or not a “chosen” node is present. So we would prefer a fix in the device-tree code over an architecture specific workaround. The problem with an architecture specific workaround outside of device-tree code is that it doesn’t know whether the chosen node is present. I had previously submitted a patch to remove the architecture specific command line code because it duplicated code in drivers/of/fdt.c and resulted in the built-in command being appended twice if the chosen node was present. It was only later that we became aware that it was not possible to use the built-in command line if the “chosen” node was not present.

>> +#endif
>> +no_data:
>> +	return 0;
>> }
>> 
>> #ifdef CONFIG_HAVE_MEMBLOCK
>> -- 
>> 2.16.1

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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.
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