  bi_vcnt .   ,    -
  ,    bi_idx,   -
    .  . 13.2   
 bio, bio_vec  page.

 bi_idx     bio_vec  ,  -
   -    
 -.       , 
  ,  RAID (Redundant Array of Inexpensive/Independent
Disks,  /      -
    ,     
         -
  ),    bio,   
  ,    ,  -
   RAID . ,     RAID,
      bio,  
 ,        bi_idx,  
    ,       
-.

 bio   ,    
bi_cnt.       ,  , 
  .      -
 .

void bio_get(struct bio *bio)
void bio put(struct bio *bio)

      ,   
      ,    
 ,    bio.    
   bio,    , 
,         . 
     .

 ,  bio_private      () -
.  ,        , 
    bio.

    

      bio   -
.  bio   -,   
      .   ,  
    ,       -
.        
 -  ,    ,   ,   -
  .    bio  ,  -
          
 -  .

   struct buffer_head   struct bio 
    .

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