b4d909d415
This patch separates the character and block driver communication protocols. The old character protocol remains the same, but a new block protocol is introduced. The libdriver library is replaced by two new libraries: libchardriver and libblockdriver. Their exposed API, and drivers that use them, have been updated accordingly. Together, libbdev and libblockdriver now completely abstract away the message format used by the block protocol. As the memory driver is both a character and a block device driver, it now implements its own message loop. The most important semantic change made to the block protocol is that it is no longer possible to return both partial results and an error for a single transfer. This simplifies the interaction between the caller and the driver, as the I/O vector no longer needs to be copied back. Also, drivers are now no longer supposed to decide based on the layout of the I/O vector when a transfer should be cut short. Put simply, transfers are now supposed to either succeed completely, or result in an error. After this patch, the state of the various pieces is as follows: - block protocol: stable - libbdev API: stable for synchronous communication - libblockdriver API: needs slight revision (the drvlib/partition API in particular; the threading API will also change shortly) - character protocol: needs cleanup - libchardriver API: needs cleanup accordingly - driver restarts: largely unsupported until endpoint changes are reintroduced As a side effect, this patch eliminates several bugs, hacks, and gcc -Wall and -W warnings all over the place. It probably introduces a few new ones, too. Update warning: this patch changes the protocol between MFS and disk drivers, so in order to use old/new images, the MFS from the ramdisk must be used to mount all file systems.
115 lines
3.2 KiB
C
115 lines
3.2 KiB
C
/* The file system maintains a buffer cache to reduce the number of disk
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* accesses needed. Whenever a read or write to the disk is done, a check is
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* first made to see if the block is in the cache. This file manages the
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* cache.
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*
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* The entry points into this file are:
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* get_block: request to fetch a block for reading or writing from cache
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* put_block: return a block previously requested with get_block
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*
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* Private functions:
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* read_block: read physically the block
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*/
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#include "inc.h"
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#include <minix/com.h>
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#include <minix/u64.h>
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#include <minix/bdev.h>
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#include "buf.h"
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FORWARD _PROTOTYPE(int read_block, (struct buf *));
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PUBLIC struct buf *bp_to_pickup = buf; /* This is a pointer to the next node in the
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* buffer cache to pick up*/
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/*===========================================================================*
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* get_block *
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*===========================================================================*/
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PUBLIC struct buf *get_block(block)
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register block_t block; /* which block is wanted? */
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{
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register struct buf *bp, *free_bp;
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free_bp = NULL;
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/* Find if the block is already loaded */
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for (bp = &buf[0]; bp < &buf[NR_BUFS]; bp++)
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if (bp->b_blocknr == block) {
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/* Block found. Increment count and return it */
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bp->b_count++;
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return bp;
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} else
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if (bp == bp_to_pickup) {
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if (bp->b_count == 0)
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free_bp = bp;
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else /* Increment the node to pickup */
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if (bp_to_pickup < &buf[NR_BUFS] - 1)
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bp_to_pickup++;
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else
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bp_to_pickup = buf;
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}
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if (free_bp == NULL &&
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bp_to_pickup == buf &&
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bp_to_pickup->b_count == 0)
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free_bp = bp_to_pickup;
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if (free_bp != NULL) {
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/* Set fields of data structure */
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free_bp->b_blocknr = block;
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if (read_block(free_bp) != OK) return NULL;
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free_bp->b_count = 1;
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if (bp_to_pickup < &buf[NR_BUFS] - 1)
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bp_to_pickup++;
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else
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bp_to_pickup = buf;
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return free_bp;
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} else {
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/* No free blocks. Return NULL */
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return NULL;
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}
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}
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/*===========================================================================*
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* put_block *
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*===========================================================================*/
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PUBLIC void put_block(bp)
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register struct buf *bp; /* pointer to the buffer to be released */
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{
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if (bp == NULL) return; /* it is easier to check here than in caller */
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bp->b_count--; /* there is one use fewer now */
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}
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/*===========================================================================*
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* read_block *
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*===========================================================================*/
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PRIVATE int read_block(bp)
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register struct buf *bp; /* buffer pointer */
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{
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int r;
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u64_t pos;
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vir_bytes block_size;
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block_size = v_pri.logical_block_size_l; /* The block size is indicated by
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* the superblock */
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pos = mul64u(bp->b_blocknr, block_size); /* get absolute position */
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r = bdev_read(fs_dev, pos, bp->b_data, block_size, BDEV_NOFLAGS);
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if (r != (ssize_t) block_size) {
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if (r == OK) r = END_OF_FILE;
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else printf("ISOFS(%d) I/O error on device %d/%d, block %u\n",
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SELF_E, (fs_dev>>MAJOR)&BYTE, (fs_dev>>MINOR)&BYTE,
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bp->b_blocknr);
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rdwt_err = r;
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return EINVAL;
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}
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return OK;
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}
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