postreview fixes

fixed bug in the pagecache which lead to assertion in multithread test


include/pagecache.h:
  post review fixes:
   - comments fixed
   - types fixed
   - keyword 'extern' added to all interface functions
mysys/mf_pagecache.c:
  postreview fixes:
   - comments fixed and added
   - types fixed
   - typo fixed
  Added write locking flag set when we took a block from LRU and going to free it (to prevent locking/using it for write)
mysys/test_pagecache_consist.c:
  pagecache size reduced (to be able reproduce problems found by Guilhem)
  typo in the comment fixed

include/pagecache.h

@@ -119,14 +119,14 @@ typedef struct st_pagecache
   ulonglong time;                /* total number of block link operations    */
   uint hash_entries;             /* max number of entries in the hash table  */
   int hash_links;                /* max number of hash links                 */
-  int hash_links_used;           /* number of hash links currently used      */
+  int hash_links_used;    /* number of hash links taken from free links pool */
   int disk_blocks;               /* max number of blocks in the cache        */
   ulong blocks_used;           /* maximum number of concurrently used blocks */
   ulong blocks_unused;           /* number of currently unused blocks        */
   ulong blocks_changed;          /* number of currently dirty blocks         */
   ulong warm_blocks;             /* number of blocks in warm sub-chain       */
   ulong cnt_for_resize_op;       /* counter to block resize operation        */
-  long blocks_available;      /* number of blocks available in the LRU chain */
+  ulong blocks_available;     /* number of blocks available in the LRU chain */
   PAGECACHE_HASH_LINK **hash_root;/* arr. of entries into hash table buckets */
   PAGECACHE_HASH_LINK *hash_link_root;/* memory for hash table links         */
   PAGECACHE_HASH_LINK *free_hash_list;/* list of free hash links             */
@@ -194,28 +194,28 @@ extern my_bool pagecache_write(PAGECACHE *pagecache,
                                enum pagecache_page_pin pin,
                                enum pagecache_write_mode write_mode,
                                PAGECACHE_PAGE_LINK *link);
-void pagecache_unlock_page(PAGECACHE *pagecache,
+extern void pagecache_unlock_page(PAGECACHE *pagecache,
                                   PAGECACHE_FILE *file,
                                   maria_page_no_t pageno,
                                   enum pagecache_page_lock lock,
                                   enum pagecache_page_pin pin,
                                   my_bool stamp_this_page,
                                   LSN first_REDO_LSN_for_page);
-void pagecache_unlock(PAGECACHE *pagecache,
+extern void pagecache_unlock(PAGECACHE *pagecache,
                              PAGECACHE_PAGE_LINK *link,
                              enum pagecache_page_lock lock,
                              enum pagecache_page_pin pin,
                              my_bool stamp_this_page,
                              LSN first_REDO_LSN_for_page);
-void pagecache_unpin_page(PAGECACHE *pagecache,
+extern void pagecache_unpin_page(PAGECACHE *pagecache,
                                  PAGECACHE_FILE *file,
                                  maria_page_no_t pageno);
-void pagecache_unpin(PAGECACHE *pagecache,
+extern void pagecache_unpin(PAGECACHE *pagecache,
                             PAGECACHE_PAGE_LINK *link);
 extern int flush_pagecache_blocks(PAGECACHE *keycache,
                                   PAGECACHE_FILE *file,
                                   enum flush_type type);
-my_bool pagecache_delete_page(PAGECACHE *pagecache,
+extern my_bool pagecache_delete_page(PAGECACHE *pagecache,
                                      PAGECACHE_FILE *file,
                                      maria_page_no_t pageno,
                                      enum pagecache_page_lock lock,

mysys/test_pagecache_consist.c

@@ -11,7 +11,7 @@
 #include <my_pthread.h>
 
 /*#define PAGE_SIZE 65536*/
-#define PCACHE_SIZE (PAGE_SIZE*1024*20)
+#define PCACHE_SIZE (PAGE_SIZE*1024*8)
 
 #ifndef DBUG_OFF
 static const char* default_dbug_option;
@@ -59,7 +59,7 @@ static uint flush_divider= 1000;
 #endif /*TEST_HIGH_CONCURENCY*/
 
 
-/* check page consistemcy */
+/* check page consistency */
 uint check_page(uchar *buff, ulong offset, int page_locked, int page_no,
                 int tag)
 {