4:33 p.m.
If the destination server supports the zero operation, and a request
includes only zeroes, use nbd_zero instead of nbd_pwrite.
To keep the example standalone, don't use common/include/iszero.h.
Implement is_zero based on Rusty Russell's blog:
https://rusty.ozlabs.org/?p=560
Signed-off-by: Nir Soffer <nsoffer(a)redhat.com>
---
examples/copy-libev.c | 94 ++++++++++++++++++++++++++++++++++++-------
1 file changed, 80 insertions(+), 14 deletions(-)
diff --git a/examples/copy-libev.c b/examples/copy-libev.c
index ca1bf3c..1b1e9df 100644
--- a/examples/copy-libev.c
+++ b/examples/copy-libev.c
@@ -61,6 +61,7 @@
struct connection {
ev_io watcher;
struct nbd_handle *nbd;
+ bool can_zero;
};
struct request {
@@ -79,9 +80,35 @@ static int64_t offset;
static int64_t written;
static bool debug;
+static void start_request(struct request *r);
static void start_read(struct request *r);
+static void start_write(struct request *r);
+static void start_zero(struct request *r);
static int read_completed(void *user_data, int *error);
-static int write_completed(void *user_data, int *error);
+static int request_completed(void *user_data, int *error);
+
+/* Return true iff data is all zero bytes.
+ *
+ * Based on Rusty Russell's memeqzero:
+ * https://rusty.ozlabs.org/?p=560
+ */
+static bool
+is_zero (const unsigned char *data, size_t len)
+{
+ const unsigned char *p = data;
+ size_t i;
+
+ for (i = 0; i < 16; i++) {
+ if (len == 0)
+ return true;
+ if (*p)
+ return false;
+ p++;
+ len--;
+ }
+
+ return memcmp (data, p, len) == 0;
+}
static inline int
get_fd(struct connection *c)
@@ -104,16 +131,25 @@ get_events(struct connection *c)
return events;
}
+/* Start async copy or zero request. */
static void
-start_read(struct request *r)
+start_request(struct request *r)
{
- int64_t cookie;
-
assert (offset < size);
r->length = MIN (REQUEST_SIZE, size - offset);
r->offset = offset;
+ start_read (r);
+
+ offset += r->length;
+}
+
+static void
+start_read(struct request *r)
+{
+ int64_t cookie;
+
DEBUG ("start read offset=%ld len=%ld", r->offset, r->length);
cookie = nbd_aio_pread (
@@ -123,38 +159,64 @@ start_read(struct request *r)
0);
if (cookie == -1)
FAIL ("Cannot start read: %s", nbd_get_error ());
-
- offset += r->length;
}
static int
read_completed (void *user_data, int *error)
{
struct request *r = (struct request *)user_data;
+
+ DEBUG ("read completed offset=%ld len=%ld", r->offset, r->length);
+
+ if (dst.can_zero && is_zero (r->data, r->length))
+ start_zero (r);
+ else
+ start_write (r);
+
+ return 1;
+}
+
+static void
+start_write(struct request *r)
+{
int64_t cookie;
- DEBUG ("read completed, starting write offset=%ld len=%ld",
- r->offset, r->length);
+ DEBUG ("start write offset=%ld len=%ld", r->offset, r->length);
cookie = nbd_aio_pwrite (
dst.nbd, r->data, r->length, r->offset,
- (nbd_completion_callback) { .callback=write_completed,
+ (nbd_completion_callback) { .callback=request_completed,
.user_data=r },
0);
if (cookie == -1)
FAIL ("Cannot start write: %s", nbd_get_error ());
+}
- return 1;
+static void
+start_zero(struct request *r)
+{
+ int64_t cookie;
+
+ DEBUG ("start zero offset=%ld len=%ld", r->offset, r->length);
+
+ cookie = nbd_aio_zero (
+ dst.nbd, r->length, r->offset,
+ (nbd_completion_callback) { .callback=request_completed,
+ .user_data=r },
+ 0);
+ if (cookie == -1)
+ FAIL ("Cannot start zero: %s", nbd_get_error ());
}
+/* Called when async copy or zero request completed. */
static int
-write_completed (void *user_data, int *error)
+request_completed (void *user_data, int *error)
{
struct request *r = (struct request *)user_data;
written += r->length;
- DEBUG ("write completed offset=%ld len=%ld", r->offset, r->length);
+ DEBUG ("request completed offset=%ld len=%ld", r->offset,
r->length);
if (written == size) {
/* The last write completed. Stop all watchers and break out
@@ -168,7 +230,7 @@ write_completed (void *user_data, int *error)
/* If we have data to read, start a new read. */
if (offset < size)
- start_read(r);
+ start_request(r);
return 1;
}
@@ -239,6 +301,10 @@ main (int argc, char *argv[])
if (size > nbd_get_size (dst.nbd))
FAIL ("Destinatio is not large enough\n");
+ /* Check destination server capabilities. */
+
+ dst.can_zero = nbd_can_zero (dst.nbd) > 0;
+
/* Start the copy "loop". When request completes, it starts the
* next request, until entire image was copied. */
@@ -249,7 +315,7 @@ main (int argc, char *argv[])
if (r->data == NULL)
FAIL ("Cannot allocate buffer: %s", strerror (errno));
- start_read(r);
+ start_request(r);
}
/* Start watching events on src and dst handles. */
--
2.26.2