?? buf.h
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/* * Each buffer in the pool is usually doubly linked into 2 lists: * the device with which it is currently associated (always) * and also on a list of blocks available for allocation * for other use (usually). * The latter list is kept in last-used order, and the two * lists are doubly linked to make it easy to remove * a buffer from one list when it was found by * looking through the other. * A buffer is on the available list, and is liable * to be reassigned to another disk block, if and only * if it is not marked BUSY. When a buffer is busy, the * available-list pointers can be used for other purposes. * Most drivers use the forward ptr as a link in their I/O * active queue. * A buffer header contains all the information required * to perform I/O. * Most of the routines which manipulate these things * are in bio.c. */struct buf{ int b_flags; /* see defines below */ struct buf *b_forw; /* headed by d_tab of conf.c */ struct buf *b_back; /* " */ struct buf *av_forw; /* position on free list, */ struct buf *av_back; /* if not BUSY*/ dev_t b_dev; /* major+minor device name */ unsigned b_bcount; /* transfer count */ union { caddr_t b_addr; /* low order core address */ int *b_words; /* words for clearing */ struct filsys *b_filsys; /* superblocks */ struct dinode *b_dino; /* ilist */ daddr_t *b_daddr; /* indirect block */ } b_un; daddr_t b_blkno; /* block # on device */ char b_xmem; /* high order core address */ char b_error; /* returned after I/O */ unsigned int b_resid; /* words not transferred after error */};extern struct buf buf[]; /* The buffer pool itself */extern struct buf bfreelist; /* head of available list *//* * These flags are kept in b_flags. */#define B_WRITE 0 /* non-read pseudo-flag */#define B_READ 01 /* read when I/O occurs */#define B_DONE 02 /* transaction finished */#define B_ERROR 04 /* transaction aborted */#define B_BUSY 010 /* not on av_forw/back list */#define B_PHYS 020 /* Physical IO potentially using UNIBUS map */#define B_MAP 040 /* This block has the UNIBUS map allocated */#define B_WANTED 0100 /* issue wakeup when BUSY goes off */#define B_AGE 0200 /* delayed write for correct aging */#define B_ASYNC 0400 /* don't wait for I/O completion */#define B_DELWRI 01000 /* don't write till block leaves available list */#define B_TAPE 02000 /* this is a magtape (no bdwrite) */#define B_PBUSY 04000#define B_PACK 010000/* * special redeclarations for * the head of the queue per * device driver. */#define b_actf av_forw#define b_actl av_back#define b_active b_bcount#define b_errcnt b_resid
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