pstore/zone,blk: Add support for pmsg frontend

Add pmsg support to pstore/blk (through pstore/zone). To enable, pmsg_size
must be greater than 0 and a multiple of 4096.
Signed-off-by: WeiXiong Liao <liaoweixiong@allwinnertech.com>
Link: https://lore.kernel.org/lkml/20200511233229.27745-4-keescook@chromium.org/Co-developed-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/lkml/20200512171932.222102-1-colin.king@canonical.comCo-developed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>

fs/pstore/Kconfig

@@ -224,3 +224,15 @@ config PSTORE_BLK_MAX_REASON
 
 	  NOTE that, both Kconfig and module parameters can configure
 	  pstore/blk, but module parameters have priority over Kconfig.
+
+config PSTORE_BLK_PMSG_SIZE
+	int "Size in Kbytes of pmsg to store"
+	depends on PSTORE_BLK
+	depends on PSTORE_PMSG
+	default 64
+	help
+	  This just sets size of pmsg (pmsg_size) for pstore/blk. The size is
+	  in KB and must be a multiple of 4.
+
+	  NOTE that, both Kconfig and module parameters can configure
+	  pstore/blk, but module parameters have priority over Kconfig.

fs/pstore/blk.c

@@ -27,6 +27,14 @@ module_param(max_reason, int, 0400);
 MODULE_PARM_DESC(max_reason,
 		 "maximum reason for kmsg dump (default 2: Oops and Panic)");
 
+#if IS_ENABLED(CONFIG_PSTORE_PMSG)
+static long pmsg_size = CONFIG_PSTORE_BLK_PMSG_SIZE;
+#else
+static long pmsg_size = -1;
+#endif
+module_param(pmsg_size, long, 0400);
+MODULE_PARM_DESC(pmsg_size, "pmsg size in kbytes");
+
 /*
  * blkdev - the block device to use for pstore storage
  *
@@ -133,6 +141,7 @@ static int psblk_register_do(struct pstore_device_info *dev)
 	}
 
 	verify_size(kmsg_size, 4096, dev->flags & PSTORE_FLAGS_DMESG);
+	verify_size(pmsg_size, 4096, dev->flags & PSTORE_FLAGS_PMSG);
 #undef verify_size
 
 	pstore_zone_info->total_size = dev->total_size;

include/linux/pstore_zone.h

@@ -17,6 +17,7 @@ typedef ssize_t (*pstore_zone_write_op)(const char *, size_t, loff_t);
  * @kmsg_size:	The size of oops/panic zone. Zero means disabled, otherwise,
  *		it must be multiple of SECTOR_SIZE(512 Bytes).
  * @max_reason: Maximum kmsg dump reason to store.
+ * @pmsg_size:	The size of pmsg zone which is the same as @kmsg_size.
  * @read:	The general read operation. Both of the function parameters
  *		@size and @offset are relative value to storage.
  *		On success, the number of bytes should be returned, others
@@ -33,6 +34,7 @@ struct pstore_zone_info {
 	unsigned long total_size;
 	unsigned long kmsg_size;
 	int max_reason;
+	unsigned long pmsg_size;
 	pstore_zone_read_op read;
 	pstore_zone_write_op write;
 	pstore_zone_write_op panic_write;