/*
* Unlike its sync counterpart, this function issues ios even for cached blocks.
*/
static errcode_t io_cache_vec_read_blocks(io_channel *channel,
struct io_vec_unit *ivus,
int count, bool nocache)
{
struct io_cache *ic = channel->io_cache;
struct io_cache_block *icb;
errcode_t ret = 0;
int i, j, blksize = channel->io_blksize;
uint64_t blkno;
uint32_t numblks;
char *buf;
/*
* Read all blocks. We could extend this to not issue ios for already
* cached blocks. But is it worth the effort?
*/
ret = unix_vec_read_blocks(channel, ivus, count);
if (ret)
goto out;
/* refresh cache */
for (i = 0; i < count; i++) {
blkno = ivus[i].ivu_blkno;
numblks = ivus[i].ivu_buflen / blksize;
buf = ivus[i].ivu_buf;
for (j = 0; j < numblks; ++j, ++blkno, buf += blksize) {
icb = io_cache_lookup(ic, blkno);
if (!icb) {
if (nocache)
continue;
icb = io_cache_pop_lru(ic);
icb->icb_blkno = blkno;
io_cache_insert(ic, icb);
}
memcpy(icb->icb_buf, buf, blksize);
if (nocache)
io_cache_unsee(ic, icb);
else
io_cache_seen(ic, icb);
}
}
out:
return ret;
}
/*
* This relies on the fact that our cache is always up to date. If a
* block is in the cache, the same thing is on disk. So here we'll write
* a whole stream and update the cache as needed.
*/
static errcode_t io_cache_write_blocks(io_channel *channel, int64_t blkno,
int count, const char *data,
bool nocache)
{
int i, completed = 0;
errcode_t ret;
struct io_cache *ic = channel->io_cache;
struct io_cache_block *icb;
/* Get the write out of the way */
ret = unix_io_write_block_full(channel, blkno, count, data,
&completed);
/*
* Now we sync up the cache with the data buffer. We have
* to sync up I/O that completed, even if the entire I/O did not.
*
* In the nocache case, we want to skip blocks that weren't in the
* cache, but we want to update blocks that where. Even though
* the caller specified "don't cache this", it's already in the
* cache. We don't want stale data.
*/
for (i = 0; i < completed; i++, data += channel->io_blksize) {
icb = io_cache_lookup(ic, blkno + i);
if (!icb) {
if (nocache)
continue;
/*
* Steal the LRU buffer. We can't error here, so
* we can safely insert it before we copy the data.
*/
icb = io_cache_pop_lru(ic);
icb->icb_blkno = blkno + i;
io_cache_insert(ic, icb);
}
memcpy(icb->icb_buf, data, channel->io_blksize);
if (nocache)
io_cache_unsee(ic, icb);
else
io_cache_seen(ic, icb);
}
return ret;
}
/*
* This relies on the fact that our cache is always up to date. If a
* block is in the cache, the same thing is on disk. Even if we re-read
* the disk block, we don't need to update the cache. This allows us
* to look for optimal I/O sizes; it's better to call one read 1MB of
* half-cached blocks than to read every other block.
*
* If the caller specifies "nocache", we still want to give them anything
* we found in the cache, but we want cached blocks moved to the front
* of the LRU. That way they get stolen first.
*/
static errcode_t io_cache_read_blocks(io_channel *channel, int64_t blkno,
int count, char *data, bool nocache)
{
int i, good_blocks;
errcode_t ret = 0;
struct io_cache *ic = channel->io_cache;
struct io_cache_block *icb;
/*
* Here we check two things:
*
* 1) Are all the blocks cached? If so, we can skip I/O.
* 2) If they are not all cached, we want to start our read at the
* first uncached blkno.
*/
for (good_blocks = 0; good_blocks < count; good_blocks++) {
icb = io_cache_lookup(ic, blkno + good_blocks);
if (!icb)
break;
}
/* Read any blocks not in the cache */
if (good_blocks < count) {
ret = unix_io_read_block(channel, blkno + good_blocks,
count - good_blocks,
data + (channel->io_blksize *
good_blocks));
if (ret)
goto out;
}
/* Now we sync up the cache with the data buffer */
for (i = 0; i < count; i++, data += channel->io_blksize) {
icb = io_cache_lookup(ic, blkno + i);
if (i < good_blocks) {
/*
* We skipped reading this because it was in the
* cache. Copy it to the data buffer.
*/
assert(icb);
memcpy(data, icb->icb_buf, channel->io_blksize);
} else if (!icb) {
if (nocache)
continue;
/* Steal the LRU buffer */
icb = io_cache_pop_lru(ic);
icb->icb_blkno = blkno + i;
io_cache_insert(ic, icb);
/*
* We did I/O into the data buffer, now update
* the cache.
*/
memcpy(icb->icb_buf, data, channel->io_blksize);
}
/*
* What about if ((i >= good_blocks) && icb)? That means
* we had the buffer in the cache, but we read it anyway
* to get a single I/O. Our cache guarantees that the
* contents will match, so we just skip to marking the
* buffer seen.
*/
if (nocache)
io_cache_unsee(ic, icb);
else
io_cache_seen(ic, icb);
}
out:
return ret;
}
