Re: udev and sysfs permissions

[Greg KH <greg@kroah.com>]

On Fri, May 27, 2005 at 06:02:28PM +0530, Maneesh Soni wrote:
> On Thu, May 26, 2005 at 04:09:51PM -0700, Greg KH wrote:
> > On Sat, May 21, 2005 at 12:07:23AM +0200, Kay Sievers wrote:
> > > On Fri, 2005-05-20 at 17:53 -0400, Jon Smirl wrote:
> > > > On 5/20/05, Greg KH <greg@kroah.com> wrote:
> > > > > On Fri, May 20, 2005 at 05:40:05PM -0400, Jon Smirl wrote:
> > > > > > On 5/20/05, Greg KH <greg@kroah.com> wrote:
> > > > > > > > That would make things simpler for driver writers if more devices are
> > > > > > > > going to follow this model.
> > > > > > >
> > > > > > > I think you are going to be pretty unique here, as no one else has come
> > > > > > > up with a situation yet that requires this.
> > > > > >
> > > > > > If the mantra about sysfs attributes being superior to IOCTLs is true,
> > > > > > then anyone who converts to sysfs attributes is going to run into this
> > > > > > problem.  In the IOCTL model permission obviously follows the owner of
> > > > > > the /dev device. There is no parallel for this in the sysfs model.
> > > > > 
> > > > > True.  Hm, let me look into the sysfs code to see if we can just save
> > > > > the changed attributes, so that they do not get lost.  That would be the
> > > > > simplest solution, right?
> > 
> > Ugh, in trying to figure this out for the past few days, I've gotten no
> > where at all :(
> > 
> > Maneesh, any chance we could get some help?  The issue is, if a user
> > changes the owner:group or permissions on a sysfs file, it would be nice
> > to have those changes stay.  Due to the backing-store changes, over
> > time, the sysfs files are re-created, and those user-made changes are
> > lost.  I've poked around in sysfs, and tried to add some new functions
> > for the vfs to call when an inode is dirty, but had no luck at all in
> > getting this to work.  Any ideas?
> > 
> 
> It should be doable. But again this will increase the size of sysfs_dirent 
> structure. If I am not wrong we will need to save (persistent) struct iattr 
> for each sysfs_dirent there by increasing its size by 52 bytes on i386 and
> we will need ->i_op->setattr() and ->i_op->getattr() routines for sysfs. 

Why do we need to increase the size?  We already save the mode in the
sysfs_dirent, right?  Isn't that all that is needed?  When the setattr()
function is called we can modify our s_mode variable.  Or am I missing
something obvious here?

> Do we need this functionality in all sysfs objects or only for certain type
> of sysfs objects?

Well, we don't really know which ones we need it for :(

If it's going to take up 52 extra bytes for every sysfs file in the
tree, that might not be worth it.

thanks,

greg k-h


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