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

[Dan Williams <dan.j.williams@intel.com>]

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@evilplan.org>
> >> Cc: Christoph Hellwig <hch@lst.de>
> >> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.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?

diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
index 87f241825bc3..39b8455f0ba5 100644
--- a/drivers/virt/coco/sev-guest/sev-guest.c
+++ b/drivers/virt/coco/sev-guest/sev-guest.c
@@ -968,7 +968,7 @@ static int __init sev_guest_probe(struct platform_device *pdev)
 	snp_dev->input.resp_gpa = __pa(snp_dev->response);
 	snp_dev->input.data_gpa = __pa(snp_dev->certs_data);
 
-	ret = tsm_register(&sev_tsm_ops, snp_dev, &tsm_report_extra_type);
+	ret = tsm_register(&sev_tsm_ops, snp_dev);
 	if (ret)
 		goto e_free_cert_data;
 
diff --git a/drivers/virt/coco/tdx-guest/tdx-guest.c b/drivers/virt/coco/tdx-guest/tdx-guest.c
index 1253bf76b570..654d20ea524a 100644
--- a/drivers/virt/coco/tdx-guest/tdx-guest.c
+++ b/drivers/virt/coco/tdx-guest/tdx-guest.c
@@ -301,7 +301,7 @@ static int __init tdx_guest_init(void)
 		goto free_misc;
 	}
 
-	ret = tsm_register(&tdx_tsm_ops, NULL, NULL);
+	ret = tsm_register(&tdx_tsm_ops, NULL);
 	if (ret)
 		goto free_quote;
 
diff --git a/drivers/virt/coco/tsm.c b/drivers/virt/coco/tsm.c
index d1c2db83a8ca..b31be0e61728 100644
--- a/drivers/virt/coco/tsm.c
+++ b/drivers/virt/coco/tsm.c
@@ -14,7 +14,6 @@
 
 static struct tsm_provider {
 	const struct tsm_ops *ops;
-	const struct config_item_type *type;
 	void *data;
 } provider;
 static DECLARE_RWSEM(tsm_rwsem);
@@ -252,34 +251,18 @@ static ssize_t tsm_report_auxblob_read(struct config_item *cfg, void *buf,
 }
 CONFIGFS_BIN_ATTR_RO(tsm_report_, auxblob, NULL, TSM_OUTBLOB_MAX);
 
-#define TSM_DEFAULT_ATTRS() \
-	&tsm_report_attr_generation, \
-	&tsm_report_attr_provider
-
 static struct configfs_attribute *tsm_report_attrs[] = {
-	TSM_DEFAULT_ATTRS(),
-	NULL,
-};
-
-static struct configfs_attribute *tsm_report_extra_attrs[] = {
-	TSM_DEFAULT_ATTRS(),
-	&tsm_report_attr_privlevel,
-	&tsm_report_attr_privlevel_floor,
+	[TSM_REPORT_GENERATION] = &tsm_report_attr_generation,
+	[TSM_REPORT_PROVIDER] = &tsm_report_attr_provider,
+	[TSM_REPORT_PRIVLEVEL] = &tsm_report_attr_privlevel,
+	[TSM_REPORT_PRIVLEVEL_FLOOR] = &tsm_report_attr_privlevel_floor,
 	NULL,
 };
 
-#define TSM_DEFAULT_BIN_ATTRS() \
-	&tsm_report_attr_inblob, \
-	&tsm_report_attr_outblob
-
 static struct configfs_bin_attribute *tsm_report_bin_attrs[] = {
-	TSM_DEFAULT_BIN_ATTRS(),
-	NULL,
-};
-
-static struct configfs_bin_attribute *tsm_report_bin_extra_attrs[] = {
-	TSM_DEFAULT_BIN_ATTRS(),
-	&tsm_report_attr_auxblob,
+	[TSM_REPORT_INBLOB] = &tsm_report_attr_inblob,
+	[TSM_REPORT_OUTBLOB] = &tsm_report_attr_outblob,
+	[TSM_REPORT_AUXBLOB] = &tsm_report_attr_auxblob,
 	NULL,
 };
 
@@ -297,21 +280,12 @@ static struct configfs_item_operations tsm_report_item_ops = {
 	.release = tsm_report_item_release,
 };
 
-const struct config_item_type tsm_report_default_type = {
+static const struct config_item_type tsm_report_type = {
 	.ct_owner = THIS_MODULE,
 	.ct_bin_attrs = tsm_report_bin_attrs,
 	.ct_attrs = tsm_report_attrs,
 	.ct_item_ops = &tsm_report_item_ops,
 };
-EXPORT_SYMBOL_GPL(tsm_report_default_type);
-
-const struct config_item_type tsm_report_extra_type = {
-	.ct_owner = THIS_MODULE,
-	.ct_bin_attrs = tsm_report_bin_extra_attrs,
-	.ct_attrs = tsm_report_extra_attrs,
-	.ct_item_ops = &tsm_report_item_ops,
-};
-EXPORT_SYMBOL_GPL(tsm_report_extra_type);
 
 static struct config_item *tsm_report_make_item(struct config_group *group,
 						const char *name)
@@ -326,12 +300,38 @@ static struct config_item *tsm_report_make_item(struct config_group *group,
 	if (!state)
 		return ERR_PTR(-ENOMEM);
 
-	config_item_init_type_name(&state->cfg, name, provider.type);
+	config_item_init_type_name(&state->cfg, name, &tsm_report_type);
 	return &state->cfg;
 }
 
+static bool tsm_report_attr_visible(struct configfs_attribute *attr, int n)
+{
+	guard(rwsem_read)(&tsm_rwsem);
+	if (!provider.ops)
+		return false;
+
+	if (!provider.ops->is_visible)
+		return true;
+
+	return provider.ops->is_visible(n);
+}
+
+static bool tsm_report_bin_attr_visible(struct configfs_bin_attribute *attr,
+					int n)
+{
+	if (!provider.ops)
+		return false;
+
+	if (!provider.ops->is_bin_visible)
+		return true;
+
+	return provider.ops->is_bin_visible(n);
+}
+
 static struct configfs_group_operations tsm_report_group_ops = {
 	.make_item = tsm_report_make_item,
+	.is_visible = tsm_report_attr_visible,
+	.is_bin_visible = tsm_report_bin_attr_visible,
 };
 
 static const struct config_item_type tsm_reports_type = {
@@ -353,16 +353,10 @@ static struct configfs_subsystem tsm_configfs = {
 	.su_mutex = __MUTEX_INITIALIZER(tsm_configfs.su_mutex),
 };
 
-int tsm_register(const struct tsm_ops *ops, void *priv,
-		 const struct config_item_type *type)
+int tsm_register(const struct tsm_ops *ops, void *priv)
 {
 	const struct tsm_ops *conflict;
 
-	if (!type)
-		type = &tsm_report_default_type;
-	if (!(type == &tsm_report_default_type || type == &tsm_report_extra_type))
-		return -EINVAL;
-
 	guard(rwsem_write)(&tsm_rwsem);
 	conflict = provider.ops;
 	if (conflict) {
@@ -372,7 +366,6 @@ int tsm_register(const struct tsm_ops *ops, void *priv,
 
 	provider.ops = ops;
 	provider.data = priv;
-	provider.type = type;
 	return 0;
 }
 EXPORT_SYMBOL_GPL(tsm_register);
@@ -384,7 +377,6 @@ int tsm_unregister(const struct tsm_ops *ops)
 		return -EBUSY;
 	provider.ops = NULL;
 	provider.data = NULL;
-	provider.type = NULL;
 	return 0;
 }
 EXPORT_SYMBOL_GPL(tsm_unregister);
diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index 18677cd4e62f..213e88f4cec2 100644
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -580,6 +580,7 @@ static void detach_attrs(struct config_item * item)
 static int populate_attrs(struct config_item *item)
 {
 	const struct config_item_type *t = item->ci_type;
+	struct configfs_group_operations *ops = t->ct_group_ops;
 	struct configfs_attribute *attr;
 	struct configfs_bin_attribute *bin_attr;
 	int error = 0;
@@ -589,12 +590,17 @@ static int populate_attrs(struct config_item *item)
 		return -EINVAL;
 	if (t->ct_attrs) {
 		for (i = 0; (attr = t->ct_attrs[i]) != NULL; i++) {
+			if (ops && ops->is_visible && !ops->is_visible(attr, i))
+				continue;
 			if ((error = configfs_create_file(item, attr)))
 				break;
 		}
 	}
 	if (t->ct_bin_attrs) {
 		for (i = 0; (bin_attr = t->ct_bin_attrs[i]) != NULL; i++) {
+			if (ops && ops->is_bin_visible &&
+			    !ops->is_bin_visible(bin_attr, i))
+				continue;
 			error = configfs_create_bin_file(item, bin_attr);
 			if (error)
 				break;
diff --git a/fs/configfs/file.c b/fs/configfs/file.c
index 0ad32150611e..356d23b6b9cf 100644
--- a/fs/configfs/file.c
+++ b/fs/configfs/file.c
@@ -444,7 +444,8 @@ const struct file_operations configfs_bin_file_operations = {
  *	@attr:	atrribute descriptor.
  */
 
-int configfs_create_file(struct config_item * item, const struct configfs_attribute * attr)
+int configfs_create_file(struct config_item *item,
+			 const struct configfs_attribute *attr)
 {
 	struct dentry *dir = item->ci_dentry;
 	struct configfs_dirent *parent_sd = dir->d_fsdata;
diff --git a/include/linux/configfs.h b/include/linux/configfs.h
index 2606711adb18..31553f12db7c 100644
--- a/include/linux/configfs.h
+++ b/include/linux/configfs.h
@@ -216,6 +216,8 @@ struct configfs_group_operations {
 	struct config_group *(*make_group)(struct config_group *group, const char *name);
 	void (*disconnect_notify)(struct config_group *group, struct config_item *item);
 	void (*drop_item)(struct config_group *group, struct config_item *item);
+	bool (*is_visible)(struct configfs_attribute *attr, int n);
+	bool (*is_bin_visible)(struct configfs_bin_attribute *attr, int n);
 };
 
 struct configfs_subsystem {
diff --git a/include/linux/tsm.h b/include/linux/tsm.h
index de8324a2223c..a45b12943223 100644
--- a/include/linux/tsm.h
+++ b/include/linux/tsm.h
@@ -42,6 +42,19 @@ struct tsm_report {
 	u8 *auxblob;
 };
 
+enum tsm_attr_index {
+	TSM_REPORT_GENERATION,
+	TSM_REPORT_PROVIDER,
+	TSM_REPORT_PRIVLEVEL,
+	TSM_REPORT_PRIVLEVEL_FLOOR,
+};
+
+enum tsm_bin_attr_index {
+	TSM_REPORT_INBLOB,
+	TSM_REPORT_OUTBLOB,
+	TSM_REPORT_AUXBLOB,
+};
+
 /**
  * struct tsm_ops - attributes and operations for tsm instances
  * @name: tsm id reflected in /sys/kernel/config/tsm/report/$report/provider
@@ -55,15 +68,11 @@ struct tsm_report {
 struct tsm_ops {
 	const char *name;
 	const unsigned int privlevel_floor;
+	bool (*is_visible)(enum tsm_attr_index index);
+	bool (*is_bin_visible)(enum tsm_bin_attr_index index);
 	int (*report_new)(struct tsm_report *report, void *data);
 };
 
-extern const struct config_item_type tsm_report_default_type;
-
-/* publish @privlevel, @privlevel_floor, and @auxblob attributes */
-extern const struct config_item_type tsm_report_extra_type;
-
-int tsm_register(const struct tsm_ops *ops, void *priv,
-		 const struct config_item_type *type);
+int tsm_register(const struct tsm_ops *ops, void *priv);
 int tsm_unregister(const struct tsm_ops *ops);
 #endif /* __TSM_H */