Re: [RFC][PATCH] fs: configfs: programmatically create config groups

[Sebastian Andrzej Siewior]

On 11/26/2012 05:56 PM, Michal Nazarewicz wrote:
> > On 11/26/2012 09:35 AM, Andrzej Pietrasiewicz wrote:
> > > In some parts of the kernel (e.g. planned configfs integration into usb
> > > gadget) there is a need to programmatically create config groups
> > > (directories) but it would be preferable to disallow creating them by
> > > the user. This is more or less what default_groups used to be for.
> > > But e.g. in the mass storage gadget, after storing the number of
> > > luns (logical units) into some configfs attribute, the corresponding lun#
> > > directories should be created, their number is not known up front so
> > > default_groups are no good for this.
> > >
> > > Example:
> > >
> > > $ echo 3>   /cfg/..../mass_storage/luns
> > >
> > > causes
> > >
> > > /cfg/....../mass_storage/lun0
> > > /cfg/....../mass_storage/lun1
> > > /cfg/....../mass_storage/lun2
>
> On Mon, Nov 26 2012, Sebastian Andrzej Siewior wrote:
> > I though we did not want the luns file but instead use
> >
> > mkdir /cfg/....../mass_storage/lun0
> > mkdir /cfg/....../mass_storage/lun1
> >
> > directly.
>
> I think that's suboptimal, and we can do better.  There are too many
> corner cases (ie. what if user does âmkdir lun7â without the previous
> luns?), it adds complexity to the kernel (ie. parsing of the name), and
> the thing is overly complicated for user (âecho 5>  nlunsâ is much nicer
> than having to create 5 directories).

Wouldn't say that. It may adds complexity on another level. The target
subsystem has the same problem with adding luns and there seems nothing
wrong with having lun3 and 4 and leaving 0 and 1 unsued.
With the tcm gadget I get:

|scsi 0:0:0:2: Direct-Access     LIO-ORG  RAMDISK-MCP      4.0  PQ: 0 
ANSI: 5
|scsi 0:0:0:3: Direct-Access     LIO-ORG  FILEIO           4.0  PQ: 0 
ANSI: 5

You notice :2 and :3 instead :0 and :1. While should be there something
wrong with this?

Sebastian
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