libminixfs: add block I/O routines
The new functionality aims to save each file system server from having to implement its own block I/O routines just so that it can serve as a root file system. The new source file (bio.c) lists the requirements that file system servers have to fulfill in order to use the routines. Change-Id: Ia0190fd5c30e8c2097ed8f4b0e3ccde1827e0b92
This commit is contained in:
David van Moolenbroek
parent
c5beebb68d
commit
ebd3c0673d
@ -6,6 +6,7 @@
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#include <minix/safecopies.h>
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#include <minix/sef.h>
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#include <minix/vfsif.h>
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#include <minix/fsdriver.h>
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struct buf {
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/* Data portion of the buffer. */
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@ -40,6 +41,7 @@ int lmfs_bytes(struct buf *bp);
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int lmfs_bufs_in_use(void);
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int lmfs_nr_bufs(void);
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void lmfs_flushall(void);
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void lmfs_flushdev(dev_t dev);
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int lmfs_fs_block_size(void);
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void lmfs_may_use_vmcache(int);
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void lmfs_set_blocksize(int blocksize, int major);
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@ -77,5 +79,11 @@ void fs_blockstats(u64_t *blocks, u64_t *free, u64_t *used);
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#define END_OF_FILE (-104) /* eof detected */
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/* Block I/O helper functions. */
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void lmfs_driver(dev_t dev, char *label);
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ssize_t lmfs_bio(dev_t dev, struct fsdriver_data *data, size_t bytes,
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off_t pos, int call);
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void lmfs_bflush(dev_t dev);
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#endif /* _MINIX_FSLIB_H */
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@ -6,6 +6,6 @@ CPPFLAGS+= -D_MINIX_SYSTEM
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.include <bsd.own.mk>
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LIB= minixfs
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SRCS= fetch_credentials.c cache.c
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SRCS= fetch_credentials.c cache.c bio.c
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.include <bsd.lib.mk>
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211
minix/lib/libminixfs/bio.c
Normal file
211
minix/lib/libminixfs/bio.c
Normal file
@ -0,0 +1,211 @@
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/*
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* This file provides an implementation for block I/O functions as expected by
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* libfsdriver for root file systems. In particular, the lmfs_driver function
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* can be used to implement fdr_driver, the lmfs_bio function can be used to
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* implement the fdr_bread, fdr_bwrite, and fdr_bpeek hooks, and the the
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* lmfs_bflush function can be used to implement the fdr_bflush hook. At the
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* very least, a file system that makes use of the provided functionality
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* must adhere to the following rules:
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*
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* o it must initialize this library in order to set up a buffer pool for
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* use by these functions, using the lmfs_buf_pool function; the
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* recommended number of blocks for *non*-disk-backed file systems is
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* NR_IOREQS buffers (disk-backed file systems typically use many more);
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* o it must enable VM caching in order to support memory mapping of block
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* devices, using the lmfs_may_use_vmcache function;
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* o it must either use lmfs_flushall as implementation for the fdr_sync
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* hook, or call lmfs_flushall as part of its own fdr_sync implementation.
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*
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* In addition, a disk-backed file system (as opposed to e.g. a networked file
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* system that intends to be able to serve as a root file system) should
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* consider the following points:
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*
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* o it may restrict calls to fdr_bwrite on the mounted partition, for
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* example to the partition's first 1024 bytes; it should generally not
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* prevent that area from being written even if the file system is mounted
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* read-only;
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* o it is free to set its own block size, although the default block size
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* works fine for raw block I/O as well.
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*/
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#include <minix/drivers.h>
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#include <minix/libminixfs.h>
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#include <minix/fsdriver.h>
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#include <minix/bdev.h>
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#include <assert.h>
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/*
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* Set the driver label of the device identified by 'dev' to 'label'. While
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* 'dev' is a full device number, only its major device number is to be used.
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* This is a very thin wrapper right now, but eventually we will want to hide
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* all of libbdev from file systems that use this library, so it is a start.
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*/
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void
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lmfs_driver(dev_t dev, char *label)
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{
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bdev_driver(dev, label);
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}
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/*
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* Prefetch up to "nblocks" blocks on "dev" starting from block number "block".
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* Stop early when either the I/O request fills up or when a block is already
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* found to be in the cache. The latter is likely to happen often, since this
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* function is called before getting each block for reading. Prefetching is a
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* strictly best-effort operation, and may fail silently.
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* TODO: limit according to the number of available buffers.
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*/
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static void
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block_prefetch(dev_t dev, block_t block, block_t nblocks)
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{
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struct buf *bp, *bufs[NR_IOREQS];
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unsigned int count;
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for (count = 0; count < nblocks; count++) {
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bp = lmfs_get_block(dev, block + count, PREFETCH);
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assert(bp != NULL);
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if (lmfs_dev(bp) != NO_DEV) {
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lmfs_put_block(bp, FULL_DATA_BLOCK);
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break;
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}
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bufs[count] = bp;
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}
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if (count > 0)
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lmfs_rw_scattered(dev, bufs, count, READING);
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}
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/*
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* Perform block I/O, on "dev", starting from offset "pos", for a total of
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* "bytes" bytes. Reading, writing, and peeking are highly similar, and thus,
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* this function implements all of them. The "call" parameter indicates the
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* call type (one of FSC_READ, FSC_WRITE, FSC_PEEK). For read and write calls,
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* "data" will identify the user buffer to use; for peek calls, "data" is set
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* to NULL. In all cases, this function returns the number of bytes
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* successfully transferred, 0 on end-of-file conditions, and a negative error
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* code if no bytes could be transferred due to an error. Dirty data is not
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* flushed immediately, and thus, a successful write only indicates that the
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* data have been taken in by the cache (for immediate I/O, a character device
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* would have to be used, but MINIX3 no longer supports this), which may be
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* follwed later by silent failures, including undetected end-of-file cases.
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* In particular, write requests may or may not return 0 (EOF) immediately when
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* writing at or beyond the block device's size. i Since block I/O takes place
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* at block granularity, block-unaligned writes have to read a block from disk
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* before updating it, and that is the only possible source of actual I/O
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* errors for write calls.
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* TODO: reconsider the buffering-only approach, or see if we can at least
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* somehow throw accurate EOF errors without reading in each block first.
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*/
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ssize_t
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lmfs_bio(dev_t dev, struct fsdriver_data * data, size_t bytes, off_t pos,
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int call)
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{
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block_t block, blocks_left;
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size_t block_size, off, block_off, chunk;
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struct buf *bp;
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int r, write, how;
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if (dev == NO_DEV)
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return EINVAL;
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block_size = lmfs_fs_block_size();
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write = (call == FSC_WRITE);
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assert(block_size > 0);
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/* FIXME: block_t is 32-bit, so we have to impose a limit here. */
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if (pos < 0 || pos / block_size > UINT32_MAX || bytes > SSIZE_MAX)
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return EINVAL;
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off = 0;
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block = pos / block_size;
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block_off = (size_t)(pos % block_size);
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blocks_left = howmany(block_off + bytes, block_size);
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lmfs_reset_rdwt_err();
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r = OK;
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for (off = 0; off < bytes; off += chunk) {
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chunk = block_size - block_off;
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if (chunk > bytes - off)
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chunk = bytes - off;
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/*
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* For read requests, help the block driver form larger I/O
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* requests.
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*/
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if (!write)
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block_prefetch(dev, block, blocks_left);
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/*
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* Do not read the block from disk if we will end up
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* overwriting all of its contents.
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*/
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how = (write && chunk == block_size) ? NO_READ : NORMAL;
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bp = lmfs_get_block(dev, block, how);
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assert(bp);
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r = lmfs_rdwt_err();
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if (r == OK && data != NULL) {
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assert(lmfs_dev(bp) != NO_DEV);
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if (write) {
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r = fsdriver_copyin(data, off,
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(char *)bp->data + block_off, chunk);
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/*
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* Mark the block as dirty even if the copy
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* failed, since the copy may in fact have
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* succeeded partially. This is an interface
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* issue that should be resolved at some point,
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* but for now we do not want the cache to be
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* desynchronized from the disk contents.
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*/
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lmfs_markdirty(bp);
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} else
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r = fsdriver_copyout(data, off,
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(char *)bp->data + block_off, chunk);
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}
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lmfs_put_block(bp, FULL_DATA_BLOCK);
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if (r != OK)
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break;
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block++;
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block_off = 0;
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blocks_left--;
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}
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/*
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* If we were not able to do any I/O, return the error (or EOF, even
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* for writes). Otherwise, return how many bytes we did manage to
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* transfer.
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*/
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if (r != OK && off == 0)
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return (r == END_OF_FILE) ? 0 : r;
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return off;
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}
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/*
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* Perform a flush request on a block device, flushing and invalidating all
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* blocks associated with this device, both in the local cache and in VM.
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* This operation is called after a block device is closed and must prevent
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* that stale copies of blocks remain in any cache.
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*/
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void
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lmfs_bflush(dev_t dev)
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{
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/* First flush any dirty blocks on this device to disk. */
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lmfs_flushdev(dev);
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/* Then purge any blocks associated with the device. */
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lmfs_invalidate(dev);
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}
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@ -29,7 +29,6 @@ static unsigned int bufs_in_use;/* # bufs currently in use (not on free list)*/
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static void rm_lru(struct buf *bp);
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static void read_block(struct buf *);
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static void flushall(dev_t dev);
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static void freeblock(struct buf *bp);
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static void cache_heuristic_check(int major);
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@ -226,7 +225,7 @@ static void freeblock(struct buf *bp)
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* Avoid hysteresis by flushing all other dirty blocks for the same device.
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*/
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if (bp->lmfs_dev != NO_DEV) {
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if (!lmfs_isclean(bp)) flushall(bp->lmfs_dev);
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if (!lmfs_isclean(bp)) lmfs_flushdev(bp->lmfs_dev);
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assert(bp->lmfs_bytes == fs_block_size);
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bp->lmfs_dev = NO_DEV;
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}
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@ -579,9 +578,9 @@ void lmfs_invalidate(
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}
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/*===========================================================================*
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* flushall *
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* lmfs_flushdev *
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*===========================================================================*/
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static void flushall(dev_t dev)
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void lmfs_flushdev(dev_t dev)
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{
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/* Flush all dirty blocks for one device. */
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@ -910,7 +909,7 @@ void lmfs_flushall(void)
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struct buf *bp;
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for(bp = &buf[0]; bp < &buf[nr_bufs]; bp++)
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if(bp->lmfs_dev != NO_DEV && !lmfs_isclean(bp))
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flushall(bp->lmfs_dev);
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lmfs_flushdev(bp->lmfs_dev);
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}
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int lmfs_fs_block_size(void)
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@ -5,7 +5,6 @@
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#define _MINIX_SYSTEM
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#include <minix/libminixfs.h>
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#include <minix/sysutil.h>
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#include <minix/syslib.h>
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#include <minix/vm.h>
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@ -21,6 +20,7 @@
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#include <unistd.h>
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#include <fcntl.h>
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#include <math.h>
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#include <minix/libminixfs.h>
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int max_error = 0;
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@ -6,7 +6,6 @@
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#define _MINIX_SYSTEM 1
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#include <minix/libminixfs.h>
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#include <minix/sysutil.h>
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#include <minix/syslib.h>
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#include <minix/vm.h>
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@ -23,6 +22,7 @@
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#include <unistd.h>
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#include <fcntl.h>
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#include <math.h>
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#include <minix/libminixfs.h>
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#include "testvm.h"
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