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linux-kernelconfigkernel-module
David Lee
David Lee

Reputation: 11

How to know which CONFIG_XXX corresponding a module?

Is there a command or some tools that can help you get the corresponding CONFIG_XXX options to enable a module. For example, if I want to enable module nvme, which CONFIG_XXX should be y or m? I know there are some documents which may states the config of nvme. But I want to know if there is a command or tool which can help you get the CONFIG——XXX only if you type a command.

Thanks.

Upvotes: 0

Views: 1148

Answers (2)

sawdust
sawdust

Reputation: 17047

if I want to enable module nvme, which CONFIG_XXX should be y or m?

As far as I know, there is no documentation or single-purpose command that would report the specific configuration symbol that builds a module.
However the Makefile that actually specifies the building of the module in question is the sole authoritative source for this information.
Typically the relevant Makefile would be in the subdirectory (or the parent directory) as the source module.

If you're not sure where the source module resides, then you could search all the Makefile files in the kernel source for the conditional build of the .o object file: 

$ find . -name Makefile | xargs grep nvme.o
./drivers/nvme/host/Makefile:obj-$(CONFIG_BLK_DEV_NVME)     += nvme.o
... <irrelevant search results>
$

So the answer would be CONFIG_BLK_DEV_NVME.
Note that the subdirectory that has the relevant Makefile will also have the Kconfig file that describes the configuration symbol you just identified.

Rather than manually edit the .config file, use the make menuconfig command.
Using the menuconfig assures you that your configuration will meet all dependencies and trigger all auto-selections properly.

You can use the search feature (simply type the slash character, /, and the config name) to retrieve help text to guide you to the location of the configuration prompt.

The help text and status of CONFIG_BLK_DEV_NVME could look like:

 Symbol: BLK_DEV_NVME [=n]     
 Type  : tristate          
 Prompt: NVM Express block device    
   Location:                   
     -> Device Drivers            
 (1)   -> NVME Support         
   Defined at drivers/nvme/host/Kconfig:4         
   Depends on: PCI [=n] && BLOCK [=y]        
   Selects: NVME_CORE [=n]       
   Selected by [n]:              
   - NVM [=n] && BLOCK [=y] && PCI [=n]

The current configuration state/status of each configuration entry mentioned is displayed within square brackets and an equals sign.

The Depends on: line indicates that both CONFIG_PCI and CONFIG_BLOCK have to be enabled in order for the CONFIG_BLK_DEV_NVME prompt to be even visible.
You may have to use the search capability to convert these other CONFIG_xxx names to their menu prompts and locations.

The Selects: line indicates the other configuration entries that will be automatically enabled if this config item is selected.

The Selected by [x]: line(s) indicates the other configuration entries that could automatically enable this config item. In this case the logical expression indicates that when three other config entries are enabled, this config is also enabled automatically.

Upvotes: 4

roolebo
roolebo

Reputation: 954

You can search the options in the interactive kernel configuration menu but you have to build the menu first via make menuconfig, then type / followed by the term you're looking for. Each Symbol: in the search results is followed by the option name without CONFIG_ prefix. It also shows location of the option in the menu tree.

Some of the options are tristate: y - the feature is going to be built into the kernel image, m - the feature should reside in a loadable module, n - the feature is disabled.

You need to add CONFIG_BLK_DEV_NVME=m (either edit .config or use make menuconfig) to enable support of nvmeNnM block devices as a loadable module.

Upvotes: 0

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