/* * 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 */ #ifdef vax 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; #define paddr(X) (paddr_t)(X->b_un.b_addr) #else paddr_t b_paddr; /* physical address */ #define paddr(X) X->b_paddr #endif daddr_t b_blkno; /* block # on device */ char b_error; /* returned after I/O */ unsigned int b_resid; /* words not transferred after error */ #ifdef vax struct proc *b_proc; /* process doing physical or swap I/O */ #endif }; extern struct buf buf[]; /* The buffer pool itself */ extern struct buf bfreelist; /* head of available list */ #ifdef vax extern char buffers[][BSIZE]; #else extern char sabuf[][BSIZE]; #endif #ifdef pdp11 long bigetl(); paddr_t bufbase; #endif paddr_t ubmaddr(); /* * 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_OPEN 02000 /* open routine called */ #define B_STALE 04000 #define B_UAREA 0100000 /* add u-area to a swap operation */ /* * Fast access to buffers in cache by hashing. */ #define bhash(d,b) ((struct buf *)&hbuf[((int)d+(int)b)&v.v_hmask]) struct hbuf { int b_flags; struct buf *b_forw; struct buf *b_back; }; extern struct hbuf hbuf[];