File:buf.h - ikarishinjieva/unixV6-code-analyze-chs GitHub Wiki

4561

4562 /*

4563  * This is the head of the queue of available

4564  * buffers-- all unused except for the 2 list heads.

4565  */

4566

4567 struct buf bfreelist;

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4568

• 以下是struct buf结构中 b_flags 使用的定义常量

4569 /*

4570  * These flags are kept in b_flags.

4571  */

4572 #define B_WRITE 0 /* non-read pseudo-flag */

4573 #define B_READ 01 /* read when I/O occurs */

4574 #define B_DONE 02 /* transaction finished */

• 该缓存块读/写设备完成

4575 #define B_ERROR 04 /* transaction aborted */

• 该缓存块读/写设备出错

4576 #define B_BUSY 010 /* not on av_forw/back list */

• 该缓存块正在读/写设备，设备忙

4577 #define B_PHYS 020 /* Physical IO potentially

4578                              using the Unibus map */

4579 #define B_MAP 040 /* This block has the UNIBUS

4580                              map allocated */

4581 #define B_WANTED 0100 /* issue wakeup when

4582                              BUSY goes off */

• 有进程正在请求该缓存块

4583 #define B_RELOC 0200 /* no longer used */

4584 #define B_ASYNC 0400 /* don’t wait wait for I/O

• 该缓存块 进行异步写

4585                              completion */

4586 #define B_DELWRI 01000 /* don’t write till block

4587                              leaves available list */

• 该缓存块 进行延迟写

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• 设备缓存管理