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device: Remove some data copying between buffers.

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Callers that read larger amounts of data now get a pointer to read-only
data directly without copying it through an intermediate buffer.  This
data is owned by the device layer so the callers no longer free it.
This commit is contained in:
Alasdair G Kergon
2018-01-10 13:18:56 +00:00
parent 4d568b709c
commit dcb2a5a611
5 changed files with 21 additions and 30 deletions
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38
lib/device/dev-io.c
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@@ -284,7 +284,7 @@ static int _aligned_io(struct device_area *where, char *buffer,
where->size, (uint64_t) where->start, widened.size, (uint64_t) widened.start, dev_name(where->dev), _reason_text(reason));
}
if (!buffer_was_widened && !((uintptr_t) buffer & mask))
if (should_write && !buffer_was_widened && !((uintptr_t) buffer & mask))
/* Perform the I/O directly. */
bounce = buffer;
#ifndef DEBUG_MEM
@@ -308,7 +308,7 @@ static int _aligned_io(struct device_area *where, char *buffer,
}
#endif
devbuf = EXTRA_IO(reason) ? &where->dev->last_extra_devbuf : &where->dev->last_devbuf;
devbuf = DEV_DEVBUF(where->dev, reason);
_release_devbuf(devbuf);
devbuf->malloc_address = bounce_buf;
devbuf->buf = bounce;
@@ -345,9 +345,6 @@ static int _aligned_io(struct device_area *where, char *buffer,
}
/* read */
if (bounce_buf)
memcpy(buffer, bounce + (where->start - widened.start),
(size_t) where->size);
/* We store what we just read as it often also satisfies the next request */
devbuf->data = bounce + (where->start - widened.start);
@@ -782,7 +779,10 @@ static void _dev_inc_error_count(struct device *dev)
dev->max_error_count, dev_name(dev));
}
static int _dev_read(struct device *dev, uint64_t offset, size_t len, dev_io_reason_t reason, char *buf)
/*
* Data is returned (read-only) at dev->last_[extra_]devbuf->data
*/
static int _dev_read(struct device *dev, uint64_t offset, size_t len, dev_io_reason_t reason)
{
struct device_area where;
int ret;
@@ -797,7 +797,7 @@ static int _dev_read(struct device *dev, uint64_t offset, size_t len, dev_io_rea
where.start = offset;
where.size = len;
ret = _aligned_io(&where, buf, 0, reason);
ret = _aligned_io(&where, NULL, 0, reason);
if (!ret)
_dev_inc_error_count(dev);
@@ -814,30 +814,24 @@ char *dev_read(struct device *dev, uint64_t offset, size_t len, dev_io_reason_t
return NULL;
}
if (!_dev_read(dev, offset, len, reason, buf)) {
if (!_dev_read(dev, offset, len, reason)) {
log_error("Read from %s failed", dev_name(dev));
dm_free(buf);
return NULL;
}
memcpy(buf, DEV_DEVBUF(dev, reason)->data, len);
return buf;
}
/* Callback fn is responsible for dm_free */
int dev_read_callback(struct device *dev, uint64_t offset, size_t len, dev_io_reason_t reason,
lvm_callback_fn_t dev_read_callback_fn, void *callback_context)
{
char *buf;
int r = 0;
if (!(buf = dm_malloc(len))) {
log_error("Buffer allocation failed for device read.");
goto out;
}
if (!_dev_read(dev, offset, len, reason, buf)) {
if (!_dev_read(dev, offset, len, reason)) {
log_error("Read from %s failed", dev_name(dev));
dm_free(buf);
goto out;
}
@@ -845,7 +839,7 @@ int dev_read_callback(struct device *dev, uint64_t offset, size_t len, dev_io_re
out:
if (dev_read_callback_fn)
dev_read_callback_fn(!r, callback_context, buf);
dev_read_callback_fn(!r, callback_context, DEV_DEVBUF(dev, reason)->data);
return r;
}
@@ -879,18 +873,22 @@ char *dev_read_circular(struct device *dev, uint64_t offset, size_t len,
return NULL;
}
if (!_dev_read(dev, offset, len, reason, buf)) {
if (!_dev_read(dev, offset, len, reason)) {
log_error("Read from %s failed", dev_name(dev));
dm_free(buf);
return NULL;
}
if (!_dev_read(dev, offset2, len2, reason, buf + len)) {
memcpy(buf, DEV_DEVBUF(dev, reason)->data, len);
if (!_dev_read(dev, offset2, len2, reason)) {
log_error("Circular read from %s failed", dev_name(dev));
dm_free(buf);
return NULL;
}
memcpy(buf + len, DEV_DEVBUF(dev, reason)->data, len2);
return buf;
}