super.h

一个简单的操作系统minix的核心代码

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				src/fs/super.h	 	 
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20700	/* Super block table.  The root file system and every mounted file system
20701	 * has an entry here.  The entry holds information about the sizes of the bit
20702	 * maps and inodes.  The s_ninodes field gives the number of inodes available
20703	 * for files and directories, including the root directory.  Inode 0 is 
20704	 * on the disk, but not used.  Thus s_ninodes = 4 means that 5 bits will be
20705	 * used in the bit map, bit 0, which is always 1 and not used, and bits 1-4
20706	 * for files and directories.  The disk layout is:
20707	 *
20708	 *      Item        # blocks
20709	 *    boot block      1
20710	 *    super block     1
20711	 *    inode map     s_imap_blocks
20712	 *    zone map      s_zmap_blocks
20713	 *    inodes        (s_ninodes + 'inodes per block' - 1)/'inodes per block'
20714	 *    unused        whatever is needed to fill out the current zone
20715	 *    data zones    (s_zones - s_firstdatazone) << s_log_zone_size
20716	 *
20717	 * A super_block slot is free if s_dev == NO_DEV. 
20718	 */
20719	
20720	
20721	EXTERN struct super_block {
20722	  ino_t s_ninodes;              /* # usable inodes on the minor device */
20723	  zone1_t  s_nzones;            /* total device size, including bit maps etc */
20724	  short s_imap_blocks;          /* # of blocks used by inode bit map */
20725	  short s_zmap_blocks;          /* # of blocks used by zone bit map */
20726	  zone1_t s_firstdatazone;      /* number of first data zone */
20727	  short s_log_zone_size;        /* log2 of blocks/zone */
20728	  off_t s_max_size;             /* maximum file size on this device */
20729	  short s_magic;                /* magic number to recognize super-blocks */
20730	  short s_pad;                  /* try to avoid compiler-dependent padding */
20731	  zone_t s_zones;               /* number of zones (replaces s_nzones in V2) */
20732	
20733	  /* The following items are only used when the super_block is in memory. */
20734	  struct inode *s_isup;         /* inode for root dir of mounted file sys */
20735	  struct inode *s_imount;       /* inode mounted on */
20736	  unsigned s_inodes_per_block;  /* precalculated from magic number */
20737	  dev_t s_dev;                  /* whose super block is this? */
20738	  int s_rd_only;                /* set to 1 iff file sys mounted read only */
20739	  int s_native;                 /* set to 1 iff not byte swapped file system */
20740	  int s_version;                /* file system version, zero means bad magic */
20741	  int s_ndzones;                /* # direct zones in an inode */
20742	  int s_nindirs;                /* # indirect zones per indirect block */
20743	  bit_t s_isearch;              /* inodes below this bit number are in use */
20744	  bit_t s_zsearch;              /* all zones below this bit number are in use*/
20745	} super_block[NR_SUPERS];
20746	
20747	#define NIL_SUPER (struct super_block *) 0
20748	#define IMAP            0       /* operating on the inode bit map */
20749	#define ZMAP            1       /* operating on the zone bit map */