text: // SPDX-License-Identifier: GPL-2.0
  /*
   * Copyright (c) 2003-2006, Cluster File Systems, Inc, info@clusterfs.com
   * Written by Alex Tomas <alex@clusterfs.com>
   */
  
  #ifndef _EXT4_EXTENTS
  #define _EXT4_EXTENTS
  
  #include "ext4.h"
  
  /*
   * With AGGRESSIVE_TEST defined, the capacity of index/leaf blocks
   * becomes very small, so index split, in-depth growing and
   * other hard changes happen much more often.
   * This is for debug purposes only.
   */
  #define AGGRESSIVE_TEST_
  
  /*
   * With EXTENTS_STATS defined, the number of blocks and extents
   * are collected in the truncate path. They'll be shown at
   * umount time.
   */
  #define EXTENTS_STATS__
  
  /*
   * If CHECK_BINSEARCH is defined, then the results of the binary search
   * will also be checked by linear search.
   */
  #define CHECK_BINSEARCH__
  
  /*
   * If EXT_STATS is defined then stats numbers are collected.
   * These number will be displayed at umount time.
   */
  #define EXT_STATS_
  
  
  /*
   * ext4_inode has i_block array (60 bytes total).
   * The first 12 bytes store ext4_extent_header;
   * the remainder stores an array of ext4_extent.
   * For non-inode extent blocks, ext4_extent_tail
   * follows the array.
   */
  
  /*
   * This is the extent tail on-disk structure.
   * All other extent structures are 12 bytes long.  It turns out that
   * block_size % 12 >= 4 for at least all powers of 2 greater than 512, which
   * covers all valid ext4 block sizes.  Therefore, this tail structure can be
   * crammed into the end of the block without having to rebalance the tree.
   */
  struct ext4_extent_tail {
  	__le32	et_checksum;	/* crc32c(uuid+inum+extent_block) */
  };
  
  /*
   * This is the extent on-disk structure.
   * It's used at the bottom of the tree.
   */
  struct ext4_extent {
  	__le32	ee_block;	/* first logical block extent covers */
  	__le16	ee_len;		/* number of blocks covered by extent */
  	__le16	ee_start_hi;	/* high 16 bits of physical block */
  	__le32	ee_start_lo;	/* low 32 bits of physical block */
  };
  
  /*
   * This is index on-disk structure.
   * It's used at all the levels except the bottom.
   */
  struct ext4_extent_idx {
  	__le32	ei_block;	/* index covers logical blocks from 'block' */
  	__le32	ei_leaf_lo;	/* pointer to the physical block of the next *
  				 * level. leaf or next index could be there */
  	__le16	ei_leaf_hi;	/* high 16 bits of physical block */
  	__u16	ei_unused;
  };
  
  /*
   * Each block (leaves and indexes), even inode-stored has header.
   */
  struct ext4_extent_header {
  	__le16	eh_magic;	/* probably will support different formats */
  	__le16	eh_entries;	/* number of valid entries */
  	__le16	eh_max;		/* capacity of store in entries */
  	__le16	eh_depth;	/* has tree real underlying blocks? */
  	__le32	eh_generation;	/* generation of the tree */
  };
  
  #define EXT4_EXT_MAGIC		cpu_to_le16(0xf30a)
  #define EXT4_MAX_EXTENT_DEPTH 5
  
  #define EXT4_EXTENT_TAIL_OFFSET(hdr) \
  	(sizeof(struct ext4_extent_header) + \
  	 (sizeof(struct ext4_extent) * le16_to_cpu((hdr)->eh_max)))
  
  static inline struct ext4_extent_tail *
  find_ext4_extent_tail(struct ext4_extent_header *eh)
  {
  	return (struct ext4_extent_tail *)(((void *)eh) +
  					   EXT4_EXTENT_TAIL_OFFSET(eh));
  }
  
  /*
   * Array of ext4_ext_path contains path to some extent.
   * Creation/lookup routines use it for traversal/splitting/etc.
   * Truncate uses it to simulate recursive walking.
   */
  struct ext4_ext_path {
  	ext4_fsblk_t			p_block;
  	__u16				p_depth;
  	__u16				p_maxdepth;
  	struct ext4_extent		*p_ext;
  	struct ext4_extent_idx		*p_idx;
  	struct ext4_extent_header	*p_hdr;
  	struct buffer_head		*p_bh;
  };
  
  /*
   * Used to record a portion of a cluster found at the beginning or end
   * of an extent while traversing the extent tree during space removal.
   * A partial cluster may be removed if it does not contain blocks shared
   * with extents that aren't being deleted (tofree state).  Otherwise,
   * it cannot be removed (nofree state).
   */
  struct partial_cluster {
  	ext4_fsblk_t pclu;  /* physical cluster number */
  	ext4_lblk_t lblk;   /* logical block number within logical cluster */
  	enum {initial, tofree, nofree} state;
  };
  
  /*
   * structure for external API
   */
  
  /*
   * EXT_INIT_MAX_LEN is the maximum number of blocks we can have in an
   * initialized extent. This is 2^15 and not (2^16 - 1), since we use the
   * MSB of ee_len field in the extent datastructure to signify if this
   * particular extent is an initialized extent or an unwritten (i.e.
   * preallocated).
   * EXT_UNWRITTEN_MAX_LEN is the maximum number of blocks we can have in an
   * unwritten extent.
   * If ee_len is <= 0x8000, it is an initialized extent. Otherwise, it is an
   * unwritten one. In other words, if MSB of ee_len is set, it is an
   * unwritten extent with only one special scenario when ee_len = 0x8000.
   * In this case we can not have an unwritten extent of zero length and
   * thus we make it as a special case of initialized extent with 0x8000 length.
   * This way we get better extent-to-group alignment for initialized extents.
   * Hence, the maximum number of blocks we can have in an *initialized*
   * extent is 2^15 (32768) and in an *unwritten* extent is 2^15-1 (32767).
   */
  #define EXT_INIT_MAX_LEN	(1UL << 15)
  #define EXT_UNWRITTEN_MAX_LEN	(EXT_INIT_MAX_LEN - 1)
  
  
  #define EXT_FIRST_EXTENT(__hdr__) \
  	((struct ext4_extent *) (((char *) (__hdr__)) +		\
  				 sizeof(struct ext4_extent_header)))
  #define EXT_FIRST_INDEX(__hdr__) \
  	((struct ext4_extent_idx *) (((char *) (__hdr__)) +	\
  				     sizeof(struct ext4_extent_header)))
  #define EXT_HAS_FREE_INDEX(__path__) \
  	(le16_to_cpu((__path__)->p_hdr->eh_entries) \
  				     < le16_to_cpu((__path__)->p_hdr->eh_max))
  #define EXT_LAST_EXTENT(__hdr__) \
  	(EXT_FIRST_EXTENT((__hdr__)) + le16_to_cpu((__hdr__)->eh_entries) - 1)
  #define EXT_LAST_INDEX(__hdr__) \
  	(EXT_FIRST_INDEX((__hdr__)) + le16_to_cpu((__hdr__)->eh_entries) - 1)
  #define EXT_MAX_EXTENT(__hdr__)	\
  	((le16_to_cpu((__hdr__)->eh_max)) ? \
  	((EXT_FIRST_EXTENT((__hdr__)) + le16_to_cpu((__hdr__)->eh_max) - 1)) \
  					: 0)
  #define EXT_MAX_INDEX(__hdr__) \
  	((le16_to_cpu((__hdr__)->eh_max)) ? \
  	((EXT_FIRST_INDEX((__hdr__)) + le16_to_cpu((__hdr__)->eh_max) - 1)) : 0)
  
  static inline struct ext4_extent_header *ext_inode_hdr(struct inode *inode)
  {
  	return (struct ext4_extent_header *) EXT4_I(inode)->i_data;
  }
  
  static inline struct ext4_extent_header *ext_block_hdr(struct buffer_head *bh)
  {
  	return (struct ext4_extent_header *) bh->b_data;
  }
  
  static inline unsigned short ext_depth(struct inode *inode)
  {
  	return le16_to_cpu(ext_inode_hdr(inode)->eh_depth);
  }
  
  static inline void ext4_ext_mark_unwritten(struct ext4_extent *ext)
  {
  	/* We can not have an unwritten extent of zero length! */
  	BUG_ON((le16_to_cpu(ext->ee_len) & ~EXT_INIT_MAX_LEN) == 0);
  	ext->ee_len |= cpu_to_le16(EXT_INIT_MAX_LEN);
  }
  
  static inline int ext4_ext_is_unwritten(struct ext4_extent *ext)
  {
  	/* Extent with ee_len of 0x8000 is treated as an initialized extent */
  	return (le16_to_cpu(ext->ee_len) > EXT_INIT_MAX_LEN);
  }
  
  static inline int ext4_ext_get_actual_len(struct ext4_extent *ext)
  {
  	return (le16_to_cpu(ext->ee_len) <= EXT_INIT_MAX_LEN ?
  		le16_to_cpu(ext->ee_len) :
  		(le16_to_cpu(ext->ee_len) - EXT_INIT_MAX_LEN));
  }
  
  static inline void ext4_ext_mark_initialized(struct ext4_extent *ext)
  {
  	ext->ee_len = cpu_to_le16(ext4_ext_get_actual_len(ext));
  }
  
  /*
   * ext4_ext_pblock:
   * combine low and high parts of physical block number into ext4_fsblk_t
   */
  static inline ext4_fsblk_t ext4_ext_pblock(struct ext4_extent *ex)
  {
  	ext4_fsblk_t block;
  
  	block = le32_to_cpu(ex->ee_start_lo);
  	block |= ((ext4_fsblk_t) le16_to_cpu(ex->ee_start_hi) << 31) << 1;
  	return block;
  }
  
  /*
   * ext4_idx_pblock:
   * combine low and high parts of a leaf physical block number into ext4_fsblk_t
   */
  static inline ext4_fsblk_t ext4_idx_pblock(struct ext4_extent_idx *ix)
  {
  	ext4_fsblk_t block;
  
  	block = le32_to_cpu(ix->ei_leaf_lo);
  	block |= ((ext4_fsblk_t) le16_to_cpu(ix->ei_leaf_hi) << 31) << 1;
  	return block;
  }
  
  /*
   * ext4_ext_store_pblock:
   * stores a large physical block number into an extent struct,
   * breaking it into parts
   */
  static inline void ext4_ext_store_pblock(struct ext4_extent *ex,
  					 ext4_fsblk_t pb)
  {
  	ex->ee_start_lo = cpu_to_le32((unsigned long) (pb & 0xffffffff));
  	ex->ee_start_hi = cpu_to_le16((unsigned long) ((pb >> 31) >> 1) &
  				      0xffff);
  }
  
  /*
   * ext4_idx_store_pblock:
   * stores a large physical block number into an index struct,
   * breaking it into parts
   */
  static inline void ext4_idx_store_pblock(struct ext4_extent_idx *ix,
  					 ext4_fsblk_t pb)
  {
  	ix->ei_leaf_lo = cpu_to_le32((unsigned long) (pb & 0xffffffff));
  	ix->ei_leaf_hi = cpu_to_le16((unsigned long) ((pb >> 31) >> 1) &
  				     0xffff);
  }
  
  #endif /* _EXT4_EXTENTS */
  
  