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

4 files changed, 153 insertions, 20 deletions

diff --git a/mysys/mf_iocache.c b/mysys/mf_iocache.c
index 0007784c2b2..709a3250f39 100644
--- a/mysys/mf_iocache.c
+++ b/mysys/mf_iocache.c
@@ -440,11 +440,24 @@ int _my_b_read(register IO_CACHE *info, byte *Buffer, uint Count)
 
   /* pos_in_file always point on where info->buffer was read */
   pos_in_file=info->pos_in_file+(uint) (info->read_end - info->buffer);
+
+  /* 
+    Whenever a function which operates on IO_CACHE flushes/writes
+    some part of the IO_CACHE to disk it will set the property
+    "seek_not_done" to indicate this to other functions operating
+    on the IO_CACHE.
+  */
   if (info->seek_not_done)
-  {					/* File touched, do seek */
-    VOID(my_seek(info->file,pos_in_file,MY_SEEK_SET,MYF(0)));
+  {
+    if (my_seek(info->file,pos_in_file,MY_SEEK_SET,MYF(0)) 
+        == MY_FILEPOS_ERROR)
+    {
+        info->error= -1;
+        DBUG_RETURN(1);
+    }
     info->seek_not_done=0;
   }
+
   diff_length=(uint) (pos_in_file & (IO_SIZE-1));
   if (Count >= (uint) (IO_SIZE+(IO_SIZE-diff_length)))
   {					/* Fill first intern buffer */
@@ -633,8 +646,22 @@ int _my_b_read_r(register IO_CACHE *info, byte *Buffer, uint Count)
     if (lock_io_cache(info, pos_in_file))
     {
       info->share->active=info;
-      if (info->seek_not_done)             /* File touched, do seek */
-        VOID(my_seek(info->file,pos_in_file,MY_SEEK_SET,MYF(0)));
+      /*
+        Whenever a function which operates on IO_CACHE flushes/writes
+        some part of the IO_CACHE to disk it will set the property
+        "seek_not_done" to indicate this to other functions operating
+        on the IO_CACHE.
+      */
+      if (info->seek_not_done)
+      {
+        if (my_seek(info->file,pos_in_file,MY_SEEK_SET,MYF(0))
+            == MY_FILEPOS_ERROR)
+        {
+          info->error= -1;
+          unlock_io_cache(info);
+          DBUG_RETURN(1);
+        }
+      }
       len=(int)my_read(info->file,info->buffer, length, info->myflags);
       info->read_end=info->buffer + (len == -1 ? 0 : len);
       info->error=(len == (int)length ? 0 : len);
@@ -668,11 +695,16 @@ int _my_b_read_r(register IO_CACHE *info, byte *Buffer, uint Count)
 
 
 /*
-  Do sequential read from the SEQ_READ_APPEND cache
-  we do this in three stages:
+  Do sequential read from the SEQ_READ_APPEND cache.
+  
+  We do this in three stages:
    - first read from info->buffer
    - then if there are still data to read, try the file descriptor
    - afterwards, if there are still data to read, try append buffer
+
+  RETURNS
+    0  Success
+    1  Failed to read
 */
 
 int _my_b_seq_read(register IO_CACHE *info, byte *Buffer, uint Count)
@@ -700,7 +732,13 @@ int _my_b_seq_read(register IO_CACHE *info, byte *Buffer, uint Count)
     With read-append cache we must always do a seek before we read,
     because the write could have moved the file pointer astray
   */
-  VOID(my_seek(info->file,pos_in_file,MY_SEEK_SET,MYF(0)));
+  if (my_seek(info->file,pos_in_file,MY_SEEK_SET,MYF(0))
+      == MY_FILEPOS_ERROR)
+  {
+   info->error= -1;
+   unlock_append_buffer(info);
+   return (1);
+  }
   info->seek_not_done=0;
 
   diff_length=(uint) (pos_in_file & (IO_SIZE-1));
@@ -816,6 +854,21 @@ read_append_buffer:
 
 #ifdef HAVE_AIOWAIT
 
+/*
+  Read from the IO_CACHE into a buffer and feed asynchronously
+  from disk when needed.
+
+  SYNOPSIS
+    _my_b_async_read()
+      info                      IO_CACHE pointer
+      Buffer                    Buffer to retrieve count bytes from file
+      Count                     Number of bytes to read into Buffer
+
+  RETURN VALUE
+    -1          An error has occurred; my_errno is set.
+     0          Success
+     1          An error has occurred; IO_CACHE to error state.
+*/
 int _my_b_async_read(register IO_CACHE *info, byte *Buffer, uint Count)
 {
   uint length,read_length,diff_length,left_length,use_length,org_Count;
@@ -906,13 +959,20 @@ int _my_b_async_read(register IO_CACHE *info, byte *Buffer, uint Count)
       info->error=(int) (read_length+left_length);
       return 1;
     }
-    VOID(my_seek(info->file,next_pos_in_file,MY_SEEK_SET,MYF(0)));
+    
+    if (my_seek(info->file,next_pos_in_file,MY_SEEK_SET,MYF(0))
+        == MY_FILEPOS_ERROR)
+    {
+      info->error= -1;
+      return (1);
+    }
+
     read_length=IO_SIZE*2- (uint) (next_pos_in_file & (IO_SIZE-1));
     if (Count < read_length)
     {					/* Small block, read to cache */
       if ((read_length=my_read(info->file,info->request_pos,
 			       read_length, info->myflags)) == (uint) -1)
-	return info->error= -1;
+        return info->error= -1;
       use_length=min(Count,read_length);
       memcpy(Buffer,info->request_pos,(size_t) use_length);
       info->read_pos=info->request_pos+Count;
@@ -999,7 +1059,15 @@ int _my_b_get(IO_CACHE *info)
   return (int) (uchar) buff;
 }
 
-	/* Returns != 0 if error on write */
+/* 
+   Write a byte buffer to IO_CACHE and flush to disk
+   if IO_CACHE is full.
+
+   RETURN VALUE
+    1 On error on write
+    0 On success
+   -1 On error; my_errno contains error code.
+*/
 
 int _my_b_write(register IO_CACHE *info, const byte *Buffer, uint Count)
 {
@@ -1022,8 +1090,18 @@ int _my_b_write(register IO_CACHE *info, const byte *Buffer, uint Count)
   {					/* Fill first intern buffer */
     length=Count & (uint) ~(IO_SIZE-1);
     if (info->seek_not_done)
-    {					/* File touched, do seek */
-      VOID(my_seek(info->file,info->pos_in_file,MY_SEEK_SET,MYF(0)));
+    {
+      /*
+        Whenever a function which operates on IO_CACHE flushes/writes
+        some part of the IO_CACHE to disk it will set the property
+        "seek_not_done" to indicate this to other functions operating
+        on the IO_CACHE.
+      */
+      if (my_seek(info->file,info->pos_in_file,MY_SEEK_SET,MYF(0)))
+      {
+        info->error= -1;
+        return (1);
+      }
       info->seek_not_done=0;
     }
     if (my_write(info->file,Buffer,(uint) length,info->myflags | MY_NABP))
diff --git a/mysys/my_chsize.c b/mysys/my_chsize.c
index cf26428d65f..b925b52ac03 100644
--- a/mysys/my_chsize.c
+++ b/mysys/my_chsize.c
@@ -88,7 +88,11 @@ int my_chsize(File fd, my_off_t newlength, int filler, myf MyFlags)
       Fill space between requested length and true length with 'filler'
       We should never come here on any modern machine
     */
-    VOID(my_seek(fd, newlength, MY_SEEK_SET, MYF(MY_WME+MY_FAE)));
+    if (my_seek(fd, newlength, MY_SEEK_SET, MYF(MY_WME+MY_FAE))
+        == MY_FILEPOS_ERROR)
+    {
+      goto err;
+    }
     swap_variables(my_off_t, newlength, oldsize);
   }
 #endif
diff --git a/mysys/my_lock.c b/mysys/my_lock.c
index 8f915d6003a..c9641f46f5c 100644
--- a/mysys/my_lock.c
+++ b/mysys/my_lock.c
@@ -35,7 +35,14 @@
 #include <nks/fsio.h>
 #endif
 
-	/* Lock a part of a file */
+/* 
+  Lock a part of a file 
+
+  RETURN VALUE
+    0   Success
+    -1  An error has occured and 'my_errno' is set
+        to indicate the actual error code.
+*/
 
 int my_lock(File fd, int locktype, my_off_t start, my_off_t length,
 	    myf MyFlags)
@@ -104,10 +111,22 @@ int my_lock(File fd, int locktype, my_off_t start, my_off_t length,
 #elif defined(HAVE_LOCKING)
   /* Windows */
   {
-    my_bool error;
+    my_bool error= false;
     pthread_mutex_lock(&my_file_info[fd].mutex);
-    if (MyFlags & MY_SEEK_NOT_DONE)
-      VOID(my_seek(fd,start,MY_SEEK_SET,MYF(MyFlags & ~MY_SEEK_NOT_DONE)));
+    if (MyFlags & MY_SEEK_NOT_DONE) 
+    {
+      if( my_seek(fd,start,MY_SEEK_SET,MYF(MyFlags & ~MY_SEEK_NOT_DONE))
+           == MY_FILEPOS_ERROR )
+      {
+        /*
+          If my_seek fails my_errno will already contain an error code;
+          just unlock and return error code.
+         */
+        DBUG_PRINT("error",("my_errno: %d (%d)",my_errno,errno));
+        pthread_mutex_unlock(&my_file_info[fd].mutex);
+        DBUG_RETURN(-1);
+      }
+    }
     error= locking(fd,locktype,(ulong) length) && errno != EINVAL;
     pthread_mutex_unlock(&my_file_info[fd].mutex);
     if (!error)
@@ -145,7 +164,17 @@ int my_lock(File fd, int locktype, my_off_t start, my_off_t length,
   }
 #else
   if (MyFlags & MY_SEEK_NOT_DONE)
-    VOID(my_seek(fd,start,MY_SEEK_SET,MYF(MyFlags & ~MY_SEEK_NOT_DONE)));
+  {
+    if (my_seek(fd,start,MY_SEEK_SET,MYF(MyFlags & ~MY_SEEK_NOT_DONE))
+        == MY_FILEPOS_ERROR)
+    {
+      /*
+        If an error has occured in my_seek then we will already
+        have an error code in my_errno; Just return error code.
+      */
+      DBUG_RETURN(-1);
+    }
+  }
   if (lockf(fd,locktype,length) != -1)
     DBUG_RETURN(0);
 #endif /* HAVE_FCNTL */
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)))