save time when creating a slab from another slab

the dns_rdataslab_fromrdataset() function creates a slab
from an rdataset. if the source rdataset already uses a slab,
then no processing is necessary; we can just copy the existing
slab to a new location.

diff --git a/lib/dns/rdataslab.c b/lib/dns/rdataslab.c
index e4fce867bae02fd89665b9a7df00be093a02592c..1aaafd0ba20a6f7e2d18fd1b458896ccdf66162e 100644 (file)
--- a/lib/dns/rdataslab.c
+++ b/lib/dns/rdataslab.c
@@ -119,6 +119,24 @@ static bool
 rdataset_equals(const dns_rdataset_t *rdataset1,
                const dns_rdataset_t *rdataset2);
 
+dns_rdatasetmethods_t dns_rdataslab_rdatasetmethods = {
+       .disassociate = rdataset_disassociate,
+       .first = rdataset_first,
+       .next = rdataset_next,
+       .current = rdataset_current,
+       .clone = rdataset_clone,
+       .count = rdataset_count,
+       .getnoqname = rdataset_getnoqname,
+       .getclosest = rdataset_getclosest,
+       .settrust = rdataset_settrust,
+       .expire = rdataset_expire,
+       .clearprefetch = rdataset_clearprefetch,
+       .setownercase = rdataset_setownercase,
+       .getownercase = rdataset_getownercase,
+       .getheader = rdataset_getheader,
+       .equals = rdataset_equals,
+};
+
 /*% Note: the "const void *" are just to make qsort happy.  */
 static int
 compare_rdata(const void *p1, const void *p2) {
@@ -136,7 +154,7 @@ makeslab(dns_rdataset_t *rdataset, isc_mem_t *mctx, isc_region_t *region,
        dns_rdata_t *rdata = NULL;
        unsigned char *rawbuf = NULL;
        unsigned int headerlen = sizeof(dns_slabheader_t);
-       unsigned int buflen;
+       unsigned int buflen = headerlen + 2;
        isc_result_t result;
        unsigned int nitems;
        unsigned int nalloc;
@@ -144,14 +162,28 @@ makeslab(dns_rdataset_t *rdataset, isc_mem_t *mctx, isc_region_t *region,
        size_t i;
        size_t rdatasize;
 
-       buflen = headerlen + 2;
+       /*
+        * If the source rdataset is also a slab, we don't need
+        * to do anything special, just copy the whole slab to a
+        * new buffer.
+        */
+       if (rdataset->methods == &dns_rdataslab_rdatasetmethods) {
+               dns_slabheader_t *header = dns_rdataset_getheader(rdataset);
+               buflen = dns_rdataslab_size(header);
 
-       nitems = dns_rdataset_count(rdataset);
+               rawbuf = isc_mem_get(mctx, buflen);
+               region->base = rawbuf;
+               region->length = buflen;
+
+               memmove(rawbuf, header, buflen);
+               return ISC_R_SUCCESS;
+       }
 
        /*
-        * If there are no rdata then we can just need to allocate a header
-        * with zero a record count.
+        * If there are no rdata then we just need to allocate a header
+        * with a zero record count.
         */
+       nitems = dns_rdataset_count(rdataset);
        if (nitems == 0) {
                if (rdataset->type != 0) {
                        return ISC_R_FAILURE;
@@ -160,8 +192,7 @@ makeslab(dns_rdataset_t *rdataset, isc_mem_t *mctx, isc_region_t *region,
                region->base = rawbuf;
                region->length = buflen;
                rawbuf += headerlen;
-               *rawbuf++ = 0;
-               *rawbuf = 0;
+               put_uint16(rawbuf, 0);
                return ISC_R_SUCCESS;
        }
 
@@ -269,9 +300,7 @@ makeslab(dns_rdataset_t *rdataset, isc_mem_t *mctx, isc_region_t *region,
 
        region->base = rawbuf;
        region->length = buflen;
-
        rawbuf += headerlen;
-
        put_uint16(rawbuf, nitems);
 
        for (i = 0; i < nalloc; i++) {
@@ -931,24 +960,6 @@ dns_slabheader_top(dns_slabheader_t *header) {
        return header;
 }
 
-dns_rdatasetmethods_t dns_rdataslab_rdatasetmethods = {
-       .disassociate = rdataset_disassociate,
-       .first = rdataset_first,
-       .next = rdataset_next,
-       .current = rdataset_current,
-       .clone = rdataset_clone,
-       .count = rdataset_count,
-       .getnoqname = rdataset_getnoqname,
-       .getclosest = rdataset_getclosest,
-       .settrust = rdataset_settrust,
-       .expire = rdataset_expire,
-       .clearprefetch = rdataset_clearprefetch,
-       .setownercase = rdataset_setownercase,
-       .getownercase = rdataset_getownercase,
-       .getheader = rdataset_getheader,
-       .equals = rdataset_equals,
-};
-
 /* Fixed RRSet helper macros */
 
 #define DNS_RDATASET_LENGTH 2;