MDEV-14378 - Allow on to drop orphaned #sql- tables

DROP TABLE now also works on empty or short .frm files

mysql-test/suite/innodb/t/alter_crash.test

@@ -95,7 +95,7 @@ FLUSH TABLES;
 
 --echo # Drop the orphaned original table.
 --disable_query_log
-eval DROP TABLE `#mysql50#$temp_table_name`;
+eval DROP TABLE `$temp_table_name`;
 --enable_query_log
 
 --echo # Files in datadir after manual recovery.

sql/datadict.cc

@@ -24,7 +24,7 @@ static int read_string(File file, uchar**to, size_t length)
 {
   DBUG_ENTER("read_string");
 
-  my_free(*to);
+  /* This can't use MY_THREAD_SPECIFIC as it's used on server start */
   if (!(*to= (uchar*) my_malloc(length+1,MYF(MY_WME))) ||
       mysql_file_read(file, *to, length, MYF(MY_NABP)))
   {
@@ -51,7 +51,7 @@ static int read_string(File file, uchar**to, size_t length)
 
   @param[out] is_sequence  1 if table is a SEQUENCE, 0 otherwise
 
-  @retval  TABLE_TYPE_UNKNOWN   error
+  @retval  TABLE_TYPE_UNKNOWN   error  - file can't be opened
   @retval  TABLE_TYPE_NORMAL    table
   @retval  TABLE_TYPE_SEQUENCE  sequence table
   @retval  TABLE_TYPE_VIEW      view
@@ -72,32 +72,35 @@ Table_type dd_frm_type(THD *thd, char *path, LEX_CSTRING *engine_name,
   if ((file= mysql_file_open(key_file_frm, path, O_RDONLY | O_SHARE, MYF(0)))
       < 0)
     DBUG_RETURN(TABLE_TYPE_UNKNOWN);
-  error= mysql_file_read(file, (uchar*) header, sizeof(header), MYF(MY_NABP));
-
-  if (error)
-    goto err;
-  if (!strncmp((char*) header, "TYPE=VIEW\n", 10))
-  {
-    type= TABLE_TYPE_VIEW;
-    goto err;
-  }
 
   /*
-    We return TABLE_TYPE_NORMAL if we can read the .frm file. This allows us
+    We return TABLE_TYPE_NORMAL if we can open the .frm file. This allows us
     to drop a bad .frm file with DROP TABLE
   */
   type= TABLE_TYPE_NORMAL;
 
-  /* engine_name is 0 if we only want to know if table is view or not */
-  if (!engine_name)
-    goto err;
-
   /*
     Initialize engine name in case we are not able to find it out
     The cast is safe, as engine_name->str points to a usable buffer.
    */
+  if (engine_name)
+  {
     engine_name->length= 0;
     ((char*) (engine_name->str))[0]= 0;
+  }
+
+  if ((error= mysql_file_read(file, (uchar*) header, sizeof(header), MYF(MY_NABP))))
+    goto err;
+
+  if (!strncmp((char*) header, "TYPE=VIEW\n", 10))
+  {
+    type= TABLE_TYPE_VIEW;
+    goto err;
+  }
+
+  /* engine_name is 0 if we only want to know if table is view or not */
+  if (!engine_name)
+    goto err;
 
   if (!is_binary_frm_header(header))
     goto err;

sql/sql_table.cc

@@ -438,6 +438,13 @@ uint check_n_cut_mysql50_prefix(const char *from, char *to, uint to_length)
 }
 
 
+static bool check_if_frm_exists(char *path, const char *db, const char *table)
+{
+  fn_format(path, table, db, reg_ext, MYF(0));
+  return !access(path, F_OK);
+}
+
+
 /*
   Translate a table name to a file name (WL #1324).
 
@@ -528,13 +535,18 @@ uint build_table_filename(char *buff, size_t bufflen, const char *db,
   DBUG_PRINT("enter", ("db: '%s'  table_name: '%s'  ext: '%s'  flags: %x",
                        db, table_name, ext, flags));
 
+  (void) tablename_to_filename(db, dbbuff, sizeof(dbbuff));
+
+  /* Check if this is a temporary table name. Allow it if a corresponding .frm file exists */
+  if (is_prefix(table_name, tmp_file_prefix) && strlen(table_name) < NAME_CHAR_LEN &&
+      check_if_frm_exists(tbbuff, dbbuff, table_name))
+    flags|= FN_IS_TMP;
+
   if (flags & FN_IS_TMP) // FN_FROM_IS_TMP | FN_TO_IS_TMP
     strmake(tbbuff, table_name, sizeof(tbbuff)-1);
   else
     (void) tablename_to_filename(table_name, tbbuff, sizeof(tbbuff));
 
-  (void) tablename_to_filename(db, dbbuff, sizeof(dbbuff));
-
   char *end = buff + bufflen;
   /* Don't add FN_ROOTDIR if mysql_data_home already includes it */
   char *pos = strnmov(buff, mysql_data_home, bufflen);