MDEV-17401: LOAD DATA from very big file into MyISAM table results in EOF error and corrupt index

my_read fixed as in higher versions.
my_pread made as my_read aware of partial read of huge chunks of files
MY_FULL_IO enabled for file operations

1 files changed, 19 insertions, 7 deletions

diff --git a/mysys/my_pread.c b/mysys/my_pread.c
index 51b4c5f5599..52d5c382960 100644
--- a/mysys/my_pread.c
+++ b/mysys/my_pread.c
@@ -47,8 +47,7 @@
 size_t my_pread(File Filedes, uchar *Buffer, size_t Count, my_off_t offset,
                 myf MyFlags)
 {
-  size_t readbytes;
-  int error= 0;
+  size_t readbytes, save_count= 0;
 
   DBUG_ENTER("my_pread");
 
@@ -66,11 +65,10 @@ size_t my_pread(File Filedes, uchar *Buffer, size_t Count, my_off_t offset,
 #else
     readbytes= pread(Filedes, Buffer, Count, offset);
 #endif
-    error = (readbytes != Count);
 
-    if (error)
+    if (readbytes != Count)
     {
-      my_errno= errno ? errno : -1;
+      my_errno= errno;
       if (errno == 0 || (readbytes != (size_t) -1 &&
                          (MyFlags & (MY_NABP | MY_FNABP))))
         my_errno= HA_ERR_FILE_TOO_SHORT;
@@ -82,6 +80,18 @@ size_t my_pread(File Filedes, uchar *Buffer, size_t Count, my_off_t offset,
                              (int) readbytes));
         continue;                              /* Interrupted */
       }
+
+      /* Do a read retry if we didn't get enough data on first read */
+      if (readbytes != (size_t) -1 && readbytes != 0 &&
+          (MyFlags & MY_FULL_IO))
+      {
+        Buffer+= readbytes;
+        Count-= readbytes;
+        save_count+= readbytes;
+        offset+= readbytes;
+        continue;
+      }
+
       if (MyFlags & (MY_WME | MY_FAE | MY_FNABP))
       {
 	if (readbytes == (size_t) -1)
@@ -97,8 +107,10 @@ size_t my_pread(File Filedes, uchar *Buffer, size_t Count, my_off_t offset,
         DBUG_RETURN(MY_FILE_ERROR);         /* Return with error */
     }
     if (MyFlags & (MY_NABP | MY_FNABP))
-      DBUG_RETURN(0);                      /* Read went ok; Return 0 */
-    DBUG_RETURN(readbytes);                /* purecov: inspected */
+      readbytes= 0;                       /* Read went ok; Return 0 */
+    else
+      readbytes+= save_count;
+    DBUG_RETURN(readbytes);
   }
 } /* my_pread */