pstore: Add priv field to pstore_record for backend specific use

The EFI pstore backend will need to store per-record variable name data
when we switch away from the efivars layer. Add a priv field to struct
pstore_record, and document it as holding a backend specific pointer
that is assumed to be a kmalloc()d buffer, and will be kfree()d when the
entire record is freed.
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

fs/pstore/inode.c

@@ -55,6 +55,7 @@ static void free_pstore_private(struct pstore_private *private)
 		return;
 	if (private->record) {
 		kfree(private->record->buf);
+		kfree(private->record->priv);
 		kfree(private->record);
 	}
 	kfree(private);

fs/pstore/platform.c

@@ -769,6 +769,7 @@ void pstore_get_backend_records(struct pstore_info *psi,
 		if (rc) {
 			/* pstore_mkfile() did not take record, so free it. */
 			kfree(record->buf);
+			kfree(record->priv);
 			kfree(record);
 			if (rc != -EEXIST || !quiet)
 				failed++;

include/linux/pstore.h

@@ -57,6 +57,9 @@ struct pstore_info;
  * @size:	size of @buf
  * @ecc_notice_size:
  *		ECC information for @buf
+ * @priv:	pointer for backend specific use, will be
+ *		kfree()d by the pstore core if non-NULL
+ *		when the record is freed.
  *
  * Valid for PSTORE_TYPE_DMESG @type:
  *
@@ -74,6 +77,7 @@ struct pstore_record {
 	char			*buf;
 	ssize_t			size;
 	ssize_t			ecc_notice_size;
+	void			*priv;
 
 	int			count;
 	enum kmsg_dump_reason	reason;