pstore/blk: Provide way to query pstore configuration

In order to configure itself, the MTD backend needs to be able to query
the current pstore configuration. Introduce pstore_blk_get_config() for
this purpose.
Signed-off-by: WeiXiong Liao <liaoweixiong@allwinnertech.com>
Link: https://lore.kernel.org/lkml/20200511233229.27745-9-keescook@chromium.org/Co-developed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>

fs/pstore/blk.c

@@ -94,6 +94,17 @@ struct bdev_info {
 	sector_t start_sect;
 };
 
+#define check_size(name, alignsize) ({				\
+	long _##name_ = (name);					\
+	_##name_ = _##name_ <= 0 ? 0 : (_##name_ * 1024);	\
+	if (_##name_ & ((alignsize) - 1)) {			\
+		pr_info(#name " must align to %d\n",		\
+				(alignsize));			\
+		_##name_ = ALIGN(name, (alignsize));		\
+	}							\
+	_##name_;						\
+})
+
 /**
  * struct pstore_device_info - back-end pstore/blk driver structure.
  *
@@ -149,13 +160,11 @@ static int psblk_register_do(struct pstore_device_info *dev)
 		dev->flags = UINT_MAX;
 
 #define verify_size(name, alignsize, enabled) {				\
-		long _##name_ = (enabled) ? (name) : 0;			\
-		_##name_ = _##name_ <= 0 ? 0 : (_##name_ * 1024);	\
-		if (_##name_ & ((alignsize) - 1)) {			\
-			pr_info(#name " must align to %d\n",		\
-					(alignsize));			\
-			_##name_ = ALIGN(name, (alignsize));		\
-		}							\
+		long _##name_;						\
+		if (enabled)						\
+			_##name_ = check_size(name, alignsize);		\
+		else							\
+			_##name_ = 0;					\
 		name = _##name_ / 1024;					\
 		pstore_zone_info->name = _##name_;			\
 	}
@@ -453,6 +462,20 @@ void unregister_pstore_blk(unsigned int major)
 }
 EXPORT_SYMBOL_GPL(unregister_pstore_blk);
 
+/* get information of pstore/blk */
+int pstore_blk_get_config(struct pstore_blk_config *info)
+{
+	strncpy(info->device, blkdev, 80);
+	info->max_reason = max_reason;
+	info->kmsg_size = check_size(kmsg_size, 4096);
+	info->pmsg_size = check_size(pmsg_size, 4096);
+	info->ftrace_size = check_size(ftrace_size, 4096);
+	info->console_size = check_size(console_size, 4096);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(pstore_blk_get_config);
+
 static void __exit pstore_blk_exit(void)
 {
 	mutex_lock(&pstore_blk_lock);

include/linux/pstore_blk.h

@@ -49,4 +49,32 @@ struct pstore_blk_info {
 int  register_pstore_blk(struct pstore_blk_info *info);
 void unregister_pstore_blk(unsigned int major);
 
+/**
+ * struct pstore_blk_config - the pstore_blk backend configuration
+ *
+ * @device:		Name of the desired block device
+ * @max_reason:		Maximum kmsg dump reason to store to block device
+ * @kmsg_size:		Total size of for kmsg dumps
+ * @pmsg_size:		Total size of the pmsg storage area
+ * @console_size:	Total size of the console storage area
+ * @ftrace_size:	Total size for ftrace logging data (for all CPUs)
+ */
+struct pstore_blk_config {
+	char device[80];
+	enum kmsg_dump_reason max_reason;
+	unsigned long kmsg_size;
+	unsigned long pmsg_size;
+	unsigned long console_size;
+	unsigned long ftrace_size;
+};
+
+/**
+ * pstore_blk_get_config - get a copy of the pstore_blk backend configuration
+ *
+ * @info:	The sturct pstore_blk_config to be filled in
+ *
+ * Failure returns negative error code, and success returns 0.
+ */
+int pstore_blk_get_config(struct pstore_blk_config *info);
+
 #endif