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@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