Bug#22828 _my_b_read() ignores return values for my_seek() calls

- Because my_seek actually is capable of returning an error code we should
  exploit that in the best possible way.
- There might be kernel errors or other errors we can't predict and capturing
  the return value of all system calls gives us better understanding of
  possible errors.


mysys/mf_iocache.c:
  - Added check on return value for my_seek
  - Added comments
mysys/my_chsize.c:
  - Added check on return value for my_seek
  - Added comments
mysys/my_lock.c:
  - Added check on return value for my_seek
  - Added comments
mysys/my_seek.c:
  - Added comments

1 files changed, 24 insertions, 2 deletions

diff --git a/mysys/my_seek.c b/mysys/my_seek.c
index 6af65d70fd0..a9ae68cd5f0 100644
--- a/mysys/my_seek.c
+++ b/mysys/my_seek.c
@@ -16,8 +16,30 @@
 
 #include "mysys_priv.h"
 
-	/* Seek to position in file */
-	/*ARGSUSED*/
+/* 
+  Seek to a position in a file.
+
+  ARGUMENTS
+  File fd          The file descriptor
+  my_off_t pos     The expected position (absolute or relative)
+  int whence       A direction parameter and one of 
+                   {SEEK_SET, SEEK_CUR, SEEK_END}
+  myf MyFlags      Not used.
+
+  DESCRIPTION
+    The my_seek  function  is a wrapper around the system call lseek and
+    repositions  the  offset of the file descriptor fd to the argument 
+    offset according to the directive whence as follows:
+      SEEK_SET    The offset is set to offset bytes.
+      SEEK_CUR    The offset is set to its current location plus offset bytes
+      SEEK_END    The offset is set to the size of the file plus offset bytes
+
+  RETURN VALUE
+    my_off_t newpos    The new position in the file.
+    MY_FILEPOS_ERROR   An error was encountered while performing 
+                       the seek. my_errno is set to indicate the
+                       actual error.
+*/
 
 my_off_t my_seek(File fd, my_off_t pos, int whence,
 		 myf MyFlags __attribute__((unused)))