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 11:01:48 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: 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

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
> 
> s/display/displayed/

Will fix.

> 
>> is displayed by default.
>>
>> 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/fs/configfs/file.c b/fs/configfs/file.c
>> index 0ad32150611e..a976c183756c 100644
>> --- a/fs/configfs/file.c
>> +++ b/fs/configfs/file.c
>> @@ -451,6 +451,9 @@ int configfs_create_file(struct config_item * item, const struct configfs_attrib
>>   	umode_t mode = (attr->ca_mode & S_IALLUGO) | S_IFREG;
>>   	int error = 0;
>>   
>> +	if (attr->is_visible && !attr->is_visible(item, attr))
>> +		return 0;
>> +
>>   	inode_lock_nested(d_inode(dir), I_MUTEX_NORMAL);
>>   	error = configfs_make_dirent(parent_sd, NULL, (void *) attr, mode,
>>   				     CONFIGFS_ITEM_ATTR, parent_sd->s_frag);
>> @@ -470,9 +473,13 @@ int configfs_create_bin_file(struct config_item *item,
>>   {
>>   	struct dentry *dir = item->ci_dentry;
>>   	struct configfs_dirent *parent_sd = dir->d_fsdata;
>> +	const struct configfs_attribute *attr = &bin_attr->cb_attr;
>>   	umode_t mode = (bin_attr->cb_attr.ca_mode & S_IALLUGO) | S_IFREG;
>>   	int error = 0;
>>   
>> +	if (attr->is_visible && !attr->is_visible(item, attr))
>> +		return 0;
>> +
>>   	inode_lock_nested(dir->d_inode, I_MUTEX_NORMAL);
>>   	error = configfs_make_dirent(parent_sd, NULL, (void *) bin_attr, mode,
>>   				     CONFIGFS_ITEM_BIN_ATTR, parent_sd->s_frag);
>> 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.

Thanks,
Tom