linux-kernel - Re: [PATCH v3 12/14] fs/configfs: Add a callback to determine attribute visibility

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Date: Tue, 16 Apr 2024 13:03:51 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Tom Lendacky <thomas.lendacky@....com>, Dan Williams
	<dan.j.williams@...el.com>, <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
	<linux-coco@...ts.linux.dev>, <svsm-devel@...onut-svsm.dev>
CC: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>, "Peter
 Zijlstra" <peterz@...radead.org>, Michael Roth <michael.roth@....com>, Ashish
 Kalra <ashish.kalra@....com>, Joel Becker <jlbec@...lplan.org>, Christoph
 Hellwig <hch@....de>
Subject: Re: [PATCH v3 12/14] fs/configfs: Add a callback to determine
 attribute visibility

Tom Lendacky wrote:
> On 4/16/24 13:25, Dan Williams wrote:
> > Tom Lendacky wrote:
> >> On 4/16/24 00:46, Dan Williams wrote:
> >>> Tom Lendacky wrote:
> >>>> In order to support dynamic decisions as to whether an attribute should be
> >>>> created, add a callback that returns a bool to indicate whether the
> >>>> attribute should be display. If no callback is registered, the attribute
> > [..]
> >>>> Cc: Joel Becker <jlbec@...lplan.org>
> >>>> Cc: Christoph Hellwig <hch@....de>
> >>>> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> >>>> ---
> >>>>    fs/configfs/file.c       |   7 +++
> >>>>    include/linux/configfs.h | 111 +++++++++++++++++++++++++++------------
> >>>>    2 files changed, 84 insertions(+), 34 deletions(-)
> >>>>
> > [..]
> >>>> diff --git a/include/linux/configfs.h b/include/linux/configfs.h
> >>>> index 2606711adb18..c836d7bc7c9e 100644
> >>>> --- a/include/linux/configfs.h
> >>>> +++ b/include/linux/configfs.h
> >>>> @@ -116,35 +116,57 @@ struct configfs_attribute {
> >>>>    	const char		*ca_name;
> >>>>    	struct module 		*ca_owner;
> >>>>    	umode_t			ca_mode;
> >>>> +	bool (*is_visible)(const struct config_item *, const struct configfs_attribute *);
> >>>>    	ssize_t (*show)(struct config_item *, char *);
> >>>>    	ssize_t (*store)(struct config_item *, const char *, size_t);
> >>>>    };
> >>>>    
> >>>> -#define CONFIGFS_ATTR(_pfx, _name)			\
> >>>> +#define __CONFIGFS_ATTR(_pfx, _name, _vis)		\
> >>>>    static struct configfs_attribute _pfx##attr_##_name = {	\
> >>>>    	.ca_name	= __stringify(_name),		\
> >>>>    	.ca_mode	= S_IRUGO | S_IWUSR,		\
> >>>>    	.ca_owner	= THIS_MODULE,			\
> >>>> +	.is_visible	= _vis,				\
> >>>>    	.show		= _pfx##_name##_show,		\
> >>>>    	.store		= _pfx##_name##_store,		\
> >>>
> >>> Shouldn't this operation live in configfs_group_operations? That would
> >>> mirror the sysfs organization, and likely saves some memory.
> >>
> >> I suppose it can, but then you lose the grouping of attributes within
> >> the same directory, right? A configfs group will result in moving the
> >> entries into a subdirectory, right? If we go with the group level, then
> >> we will be moving the existing TSM extra attributes and the new TSM SVSM
> >> attributes into new, separate sub-directories.
> > 
> > I am not following the concern about "losing the grouping"? Here is what
> > I was thinking with having the visibility routines in group operations.
> > This is just the broard strokes, it compiles, but still needs the finer
> > detail work to make tdx-guest skip all the attributes that do not apply
> > to it.  Might need to be broken up a bit more, but hopefully conveys the
> > idea. Does this address your grouping concern?
> 
> Yes and no. Basically the is_visible()/is_bin_visible() callback will 
> have to check every index value for a "group" against the passed in 
> value. I was trying to group the values together using an enum in order 
> to make it a bit easier and more readable in the callback. Adding 
> another attribute to the group requires updates in multiple places. But 
> thats just how I was looking at it. I can also see where you might want 
> to selectively hide/show entries and this method works well for that.
> 
> I'll follow this approach (add you as Co-developed-by: or Suggested-by:, 
> whichever you prefer) and submit a v4.

Sure, you can add:

Co-developed-by: Dan Williams <dan.j.williams@...el.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>

..if you want to reuse any of this sample patch.