resolve: update sd-resolve to match the other APIs in style and functionality

1 files changed, 575 insertions, 444 deletions

diff --git a/src/libsystemd/sd-resolve/sd-resolve.c b/src/libsystemd/sd-resolve/sd-resolve.c
index 464967b362..803190f02b 100644
--- a/src/libsystemd/sd-resolve/sd-resolve.c
+++ b/src/libsystemd/sd-resolve/sd-resolve.c
@@ -40,13 +40,17 @@
 #include <stdint.h>
 #include <pthread.h>
 #include <sys/prctl.h>
+#include <sys/poll.h>
 
-#include "sd-resolve.h"
 #include "util.h"
+#include "list.h"
+#include "socket-util.h"
+#include "sd-resolve.h"
 
-#define MAX_WORKERS 16
-#define MAX_QUERIES 256
-#define BUFSIZE (10240)
+#define WORKERS_MIN 1
+#define WORKERS_MAX 16
+#define QUERIES_MAX 256
+#define BUFSIZE 10240
 
 typedef enum {
         REQUEST_ADDRINFO,
@@ -61,40 +65,46 @@ typedef enum {
 } QueryType;
 
 enum {
-        REQUEST_RECV_FD = 0,
-        REQUEST_SEND_FD = 1,
-        RESPONSE_RECV_FD = 2,
-        RESPONSE_SEND_FD = 3,
-        MESSAGE_FD_MAX = 4
+        REQUEST_RECV_FD,
+        REQUEST_SEND_FD,
+        RESPONSE_RECV_FD,
+        RESPONSE_SEND_FD,
+        _FD_MAX
 };
 
 struct sd_resolve {
-        int fds[MESSAGE_FD_MAX];
+        bool dead:1;
+        pid_t original_pid;
 
-        pthread_t workers[MAX_WORKERS];
-        unsigned valid_workers;
+        int fds[_FD_MAX];
 
-        unsigned current_id, current_index;
-        sd_resolve_query* queries[MAX_QUERIES];
+        pthread_t workers[WORKERS_MAX];
+        unsigned n_valid_workers;
 
-        sd_resolve_query *done_head, *done_tail;
+        unsigned current_id, current_index;
+        sd_resolve_query* queries[QUERIES_MAX];
+        unsigned n_queries;
 
-        int n_queries;
-        int dead;
+        LIST_HEAD(sd_resolve_query, done);
+        sd_resolve_query *done_tail;
+        unsigned n_done;
 };
 
 struct sd_resolve_query {
         sd_resolve *resolve;
-        int done;
+        bool done:1;
         unsigned id;
         QueryType type;
-        sd_resolve_query *done_next, *done_prev;
+
         int ret;
         int _errno;
         int _h_errno;
         struct addrinfo *addrinfo;
         char *serv, *host;
+
         void *userdata;
+
+        LIST_FIELDS(sd_resolve_query, done);
 };
 
 typedef struct RHeader {
@@ -105,7 +115,7 @@ typedef struct RHeader {
 
 typedef struct AddrInfoRequest {
         struct RHeader header;
-        int hints_is_null;
+        bool hints_valid;
         int ai_flags;
         int ai_family;
         int ai_socktype;
@@ -135,7 +145,7 @@ typedef struct NameInfoRequest {
         struct RHeader header;
         int flags;
         socklen_t sockaddr_len;
-        int gethost, getserv;
+        bool gethost:1, getserv:1;
 } NameInfoRequest;
 
 typedef struct NameInfoResponse {
@@ -172,24 +182,28 @@ typedef union Packet {
 
 static int send_died(int out_fd) {
         RHeader rh = {};
-        assert(out_fd > 0);
+
+        assert(out_fd >= 0);
 
         rh.type = RESPONSE_DIED;
-        rh.id = 0;
         rh.length = sizeof(rh);
 
-        return send(out_fd, &rh, rh.length, MSG_NOSIGNAL);
+        if (send(out_fd, &rh, rh.length, MSG_NOSIGNAL) < 0)
+                return -errno;
+
+        return 0;
 }
 
 static void *serialize_addrinfo(void *p, const struct addrinfo *ai, size_t *length, size_t maxlength) {
         AddrInfoSerialization s;
         size_t cnl, l;
+
         assert(p);
         assert(ai);
         assert(length);
         assert(*length <= maxlength);
 
-        cnl = (ai->ai_canonname ? strlen(ai->ai_canonname)+1 : 0);
+        cnl = ai->ai_canonname ? strlen(ai->ai_canonname)+1 : 0;
         l = sizeof(AddrInfoSerialization) + ai->ai_addrlen + cnl;
 
         if (*length + l > maxlength)
@@ -206,33 +220,46 @@ static void *serialize_addrinfo(void *p, const struct addrinfo *ai, size_t *leng
         memcpy((uint8_t*) p + sizeof(AddrInfoSerialization), ai->ai_addr, ai->ai_addrlen);
 
         if (ai->ai_canonname)
-                strcpy((char*) p + sizeof(AddrInfoSerialization) + ai->ai_addrlen, ai->ai_canonname);
+                memcpy((char*) p + sizeof(AddrInfoSerialization) + ai->ai_addrlen, ai->ai_canonname, cnl);
 
         *length += l;
         return (uint8_t*) p + l;
 }
 
-static int send_addrinfo_reply(int out_fd, unsigned id, int ret, struct addrinfo *ai, int _errno, int _h_errno) {
-        AddrInfoResponse data[BUFSIZE/sizeof(AddrInfoResponse) + 1] = {};
-        AddrInfoResponse *resp = data;
+static int send_addrinfo_reply(
+                int out_fd,
+                unsigned id,
+                int ret,
+                struct addrinfo *ai,
+                int _errno,
+                int _h_errno) {
+
+        AddrInfoResponse resp = {};
+        struct msghdr mh = {};
+        struct iovec iov[2];
+        union {
+                AddrInfoSerialization ais;
+                uint8_t space[BUFSIZE];
+        } buffer;
+
         assert(out_fd >= 0);
 
-        resp->header.type = RESPONSE_ADDRINFO;
-        resp->header.id = id;
-        resp->header.length = sizeof(AddrInfoResponse);
-        resp->ret = ret;
-        resp->_errno = _errno;
-        resp->_h_errno = _h_errno;
+        resp.header.type = RESPONSE_ADDRINFO;
+        resp.header.id = id;
+        resp.header.length = sizeof(AddrInfoResponse);
+        resp.ret = ret;
+        resp._errno = _errno;
+        resp._h_errno = _h_errno;
 
         if (ret == 0 && ai) {
-                void *p = data + 1;
+                void *p = &buffer;
                 struct addrinfo *k;
 
                 for (k = ai; k; k = k->ai_next) {
-                        p = serialize_addrinfo(p, k, &resp->header.length, (char*) data + BUFSIZE - (char*) p);
+                        p = serialize_addrinfo(p, k, &resp.header.length, (uint8_t*) &buffer + BUFSIZE - (uint8_t*) p);
                         if (!p) {
-                                resp->ret = EAI_MEMORY;
-                                break;
+                                freeaddrinfo(ai);
+                                return -ENOBUFS;
                         }
                 }
         }
@@ -240,89 +267,121 @@ static int send_addrinfo_reply(int out_fd, unsigned id, int ret, struct addrinfo
         if (ai)
                 freeaddrinfo(ai);
 
-        return send(out_fd, resp, resp->header.length, MSG_NOSIGNAL);
+        iov[0] = (struct iovec) { .iov_base = &resp, .iov_len = sizeof(AddrInfoResponse) };
+        iov[1] = (struct iovec) { .iov_base = &buffer, .iov_len = resp.header.length - sizeof(AddrInfoResponse) };
+
+        mh.msg_iov = iov;
+        mh.msg_iovlen = ELEMENTSOF(iov);
+
+        if (sendmsg(out_fd, &mh, MSG_NOSIGNAL) < 0)
+                return -errno;
+
+        return 0;
 }
 
-static int send_nameinfo_reply(int out_fd, unsigned id, int ret, const char *host, const char *serv, int _errno, int _h_errno) {
-        NameInfoResponse data[BUFSIZE/sizeof(NameInfoResponse) + 1] = {};
+static int send_nameinfo_reply(
+                int out_fd,
+                unsigned id,
+                int ret,
+                const char *host,
+                const char *serv,
+                int _errno,
+                int _h_errno) {
+
+        NameInfoResponse resp = {};
+        struct msghdr mh = {};
+        struct iovec iov[3];
         size_t hl, sl;
-        NameInfoResponse *resp = data;
 
         assert(out_fd >= 0);
 
         sl = serv ? strlen(serv)+1 : 0;
         hl = host ? strlen(host)+1 : 0;
 
-        resp->header.type = RESPONSE_NAMEINFO;
-        resp->header.id = id;
-        resp->header.length = sizeof(NameInfoResponse) + hl + sl;
-        resp->ret = ret;
-        resp->_errno = _errno;
-        resp->_h_errno = _h_errno;
-        resp->hostlen = hl;
-        resp->servlen = sl;
+        resp.header.type = RESPONSE_NAMEINFO;
+        resp.header.id = id;
+        resp.header.length = sizeof(NameInfoResponse) + hl + sl;
+        resp.ret = ret;
+        resp._errno = _errno;
+        resp._h_errno = _h_errno;
+        resp.hostlen = hl;
+        resp.servlen = sl;
 
-        assert(sizeof(data) >= resp->header.length);
+        iov[0] = (struct iovec) { .iov_base = &resp, .iov_len = sizeof(NameInfoResponse) };
+        iov[1] = (struct iovec) { .iov_base = (void*) host, .iov_len = hl };
+        iov[2] = (struct iovec) { .iov_base = (void*) serv, .iov_len = sl };
 
-        if (host)
-                memcpy((uint8_t *)data + sizeof(NameInfoResponse), host, hl);
+        mh.msg_iov = iov;
+        mh.msg_iovlen = ELEMENTSOF(iov);
 
-        if (serv)
-                memcpy((uint8_t *)data + sizeof(NameInfoResponse) + hl, serv, sl);
+        if (sendmsg(out_fd, &mh, MSG_NOSIGNAL) < 0)
+                return -errno;
 
-        return send(out_fd, resp, resp->header.length, MSG_NOSIGNAL);
+        return 0;
 }
 
 static int send_res_reply(int out_fd, unsigned id, const unsigned char *answer, int ret, int _errno, int _h_errno) {
-        ResResponse data[BUFSIZE/sizeof(ResResponse) + 1] = {};
-        ResResponse *resp = data;
+        struct msghdr mh = {};
+        struct iovec iov[2];
+        ResResponse resp = {};
+        size_t l;
 
         assert(out_fd >= 0);
 
-        resp->header.type = RESPONSE_RES;
-        resp->header.id = id;
-        resp->header.length = sizeof(ResResponse) + (ret < 0 ? 0 : ret);
-        resp->ret = ret;
-        resp->_errno = _errno;
-        resp->_h_errno = _h_errno;
+        l = ret > 0 ? (size_t) ret : 0;
+
+        resp.header.type = RESPONSE_RES;
+        resp.header.id = id;
+        resp.header.length = sizeof(ResResponse) + l;
+        resp.ret = ret;
+        resp._errno = _errno;
+        resp._h_errno = _h_errno;
 
-        assert(sizeof(data) >= resp->header.length);
+        iov[0] = (struct iovec) { .iov_base = &resp, .iov_len = sizeof(ResResponse) };
+        iov[1] = (struct iovec) { .iov_base = (void*) answer, .iov_len = l };
 
-        if (ret > 0)
-                memcpy((uint8_t *)data + sizeof(ResResponse), answer, ret);
+        mh.msg_iov = iov;
+        mh.msg_iovlen = ELEMENTSOF(iov);
 
-        return send(out_fd, resp, resp->header.length, MSG_NOSIGNAL);
+        if (sendmsg(out_fd, &mh, MSG_NOSIGNAL) < 0)
+                return -errno;
+
+        return 0;
 }
 
 static int handle_request(int out_fd, const Packet *packet, size_t length) {
         const RHeader *req;
+
         assert(out_fd >= 0);
+        assert(packet);
 
         req = &packet->rheader;
-        assert(req);
+
         assert(length >= sizeof(RHeader));
         assert(length == req->length);
 
         switch (req->type) {
+
         case REQUEST_ADDRINFO: {
-               struct addrinfo ai = {}, *result = NULL;
                const AddrInfoRequest *ai_req = &packet->addrinfo_request;
+               struct addrinfo hints = {}, *result = NULL;
                const char *node, *service;
                int ret;
 
                assert(length >= sizeof(AddrInfoRequest));
                assert(length == sizeof(AddrInfoRequest) + ai_req->node_len + ai_req->service_len);
 
-               ai.ai_flags = ai_req->ai_flags;
-               ai.ai_family = ai_req->ai_family;
-               ai.ai_socktype = ai_req->ai_socktype;
-               ai.ai_protocol = ai_req->ai_protocol;
+               hints.ai_flags = ai_req->ai_flags;
+               hints.ai_family = ai_req->ai_family;
+               hints.ai_socktype = ai_req->ai_socktype;
+               hints.ai_protocol = ai_req->ai_protocol;
 
                node = ai_req->node_len ? (const char*) ai_req + sizeof(AddrInfoRequest) : NULL;
                service = ai_req->service_len ? (const char*) ai_req + sizeof(AddrInfoRequest) + ai_req->node_len : NULL;
 
-               ret = getaddrinfo(node, service,
-                               ai_req->hints_is_null ? NULL : &ai,
+               ret = getaddrinfo(
+                               node, service,
+                               ai_req->hints_valid ? &hints : NULL,
                                &result);
 
                /* send_addrinfo_reply() frees result */
@@ -330,17 +389,18 @@ static int handle_request(int out_fd, const Packet *packet, size_t length) {
         }
 
         case REQUEST_NAMEINFO: {
-               int ret;
                const NameInfoRequest *ni_req = &packet->nameinfo_request;
                char hostbuf[NI_MAXHOST], servbuf[NI_MAXSERV];
-               struct sockaddr_storage sa;
+               union sockaddr_union sa;
+               int ret;
 
                assert(length >= sizeof(NameInfoRequest));
                assert(length == sizeof(NameInfoRequest) + ni_req->sockaddr_len);
+               assert(sizeof(sa) >= ni_req->sockaddr_len);
 
                memcpy(&sa, (const uint8_t *) ni_req + sizeof(NameInfoRequest), ni_req->sockaddr_len);
 
-               ret = getnameinfo((struct sockaddr *)&sa, ni_req->sockaddr_len,
+               ret = getnameinfo(&sa.sa, ni_req->sockaddr_len,
                                ni_req->gethost ? hostbuf : NULL, ni_req->gethost ? sizeof(hostbuf) : 0,
                                ni_req->getserv ? servbuf : NULL, ni_req->getserv ? sizeof(servbuf) : 0,
                                ni_req->flags);
@@ -353,10 +413,13 @@ static int handle_request(int out_fd, const Packet *packet, size_t length) {
 
         case REQUEST_RES_QUERY:
         case REQUEST_RES_SEARCH: {
-                 int ret;
-                 HEADER answer[BUFSIZE/sizeof(HEADER) + 1];
                  const ResRequest *res_req = &packet->res_request;
+                 union {
+                         HEADER header;
+                         uint8_t space[BUFSIZE];
+                 } answer;
                  const char *dname;
+                 int ret;
 
                  assert(length >= sizeof(ResRequest));
                  assert(length == sizeof(ResRequest) + res_req->dname_len);
@@ -364,19 +427,19 @@ static int handle_request(int out_fd, const Packet *packet, size_t length) {
                  dname = (const char *) req + sizeof(ResRequest);
 
                  if (req->type == REQUEST_RES_QUERY)
-                         ret = res_query(dname, res_req->class, res_req->type, (unsigned char *) answer, BUFSIZE);
+                         ret = res_query(dname, res_req->class, res_req->type, (unsigned char *) &answer, BUFSIZE);
                  else
-                         ret = res_search(dname, res_req->class, res_req->type, (unsigned char *) answer, BUFSIZE);
+                         ret = res_search(dname, res_req->class, res_req->type, (unsigned char *) &answer, BUFSIZE);
 
-                 return send_res_reply(out_fd, req->id, (unsigned char *) answer, ret, errno, h_errno);
+                 return send_res_reply(out_fd, req->id, (unsigned char *) &answer, ret, errno, h_errno);
         }
 
         case REQUEST_TERMINATE:
                  /* Quit */
-                 return -1;
+                 return -ECONNRESET;
 
         default:
-                 ;
+                assert_not_reached("Unknown request");
         }
 
         return 0;
@@ -387,25 +450,33 @@ static void* thread_worker(void *p) {
         sigset_t fullset;
 
         /* No signals in this thread please */
-        sigfillset(&fullset);
-        pthread_sigmask(SIG_BLOCK, &fullset, NULL);
+        assert_se(sigfillset(&fullset) == 0);
+        assert_se(pthread_sigmask(SIG_BLOCK, &fullset, NULL) == 0);
+
+        /* Assign a pretty name to this thread */
+        prctl(PR_SET_NAME, (unsigned long) "sd-resolve");
 
         while (!resolve->dead) {
-                Packet buf[BUFSIZE/sizeof(Packet) + 1];
+                union {
+                        Packet packet;
+                        uint8_t space[BUFSIZE];
+                } buf;
                 ssize_t length;
 
-                length = recv(resolve->fds[REQUEST_RECV_FD], buf, sizeof(buf), 0);
-
-                if (length <= 0) {
-                        if (length < 0 && (errno == EAGAIN || errno == EINTR))
+                length = recv(resolve->fds[REQUEST_RECV_FD], &buf, sizeof(buf), 0);
+                if (length < 0) {
+                        if (errno == EINTR)
                                 continue;
+
                         break;
                 }
+                if (length == 0)
+                        break;
 
                 if (resolve->dead)
                         break;
 
-                if (handle_request(resolve->fds[RESPONSE_SEND_FD], buf, (size_t) length) < 0)
+                if (handle_request(resolve->fds[RESPONSE_SEND_FD], &buf.packet, (size_t) length) < 0)
                         break;
         }
 
@@ -414,114 +485,154 @@ static void* thread_worker(void *p) {
         return NULL;
 }
 
-_public_ sd_resolve* sd_resolve_new(unsigned n_proc) {
-        sd_resolve *resolve = NULL;
-        int i, r;
+static int start_threads(sd_resolve *resolve, unsigned extra) {
+        unsigned n;
+        int r;
 
-        assert(n_proc >= 1);
+        n = resolve->n_queries - resolve->n_done + extra;
 
-        if (n_proc > MAX_WORKERS)
-                n_proc = MAX_WORKERS;
+        if (n < WORKERS_MIN)
+                n = WORKERS_MIN;
+        if (n > WORKERS_MAX)
+                n = WORKERS_MAX;
 
-        resolve = new(sd_resolve, 1);
-        if (!resolve) {
-                errno = ENOMEM;
-                goto fail;
+        while (resolve->n_valid_workers < n) {
+
+                r = pthread_create(&resolve->workers[resolve->n_valid_workers], NULL, thread_worker, resolve);
+                if (r != 0)
+                        return -r;
+
+                resolve->n_valid_workers ++;
         }
 
-        resolve->dead = 0;
-        resolve->valid_workers = 0;
+        return 0;
+}
+
+static bool resolve_pid_changed(sd_resolve *r) {
+        assert(r);
+
+        /* We don't support people creating a resolver and keeping it
+         * around after fork(). Let's complain. */
+
+        return r->original_pid != getpid();
+}
 
-        for (i = 0; i < MESSAGE_FD_MAX; i++)
+_public_ int sd_resolve_new(sd_resolve **ret) {
+        sd_resolve *resolve = NULL;
+        int i, r;
+
+        assert_return(ret, -EINVAL);
+
+        resolve = new0(sd_resolve, 1);
+        if (!resolve)
+                return -ENOMEM;
+
+        for (i = 0; i < _FD_MAX; i++)
                 resolve->fds[i] = -1;
 
-        memset(resolve->queries, 0, sizeof(resolve->queries));
+        resolve->original_pid = getpid();
 
-        r = socketpair(PF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0, resolve->fds);
-        if (r < 0)
+        r = socketpair(PF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0, resolve->fds + REQUEST_RECV_FD);
+        if (r < 0) {
+                r = -errno;
                 goto fail;
+        }
 
-        r = socketpair(PF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0, resolve->fds+2);
-        if (r < 0)
+        r = socketpair(PF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0, resolve->fds + RESPONSE_RECV_FD);
+        if (r < 0) {
+                r = -errno;
                 goto fail;
-
-        for (resolve->valid_workers = 0; resolve->valid_workers < n_proc; resolve->valid_workers++) {
-                r = pthread_create(&resolve->workers[resolve->valid_workers], NULL, thread_worker, resolve);
-                if (r) {
-                        errno = r;
-                        goto fail;
-                }
         }
 
-        resolve->current_index = resolve->current_id = 0;
-        resolve->done_head = resolve->done_tail = NULL;
-        resolve->n_queries = 0;
+        fd_inc_sndbuf(resolve->fds[REQUEST_SEND_FD], QUERIES_MAX * BUFSIZE);
+        fd_inc_rcvbuf(resolve->fds[REQUEST_RECV_FD], QUERIES_MAX * BUFSIZE);
+        fd_inc_sndbuf(resolve->fds[RESPONSE_SEND_FD], QUERIES_MAX * BUFSIZE);
+        fd_inc_rcvbuf(resolve->fds[RESPONSE_RECV_FD], QUERIES_MAX * BUFSIZE);
 
         fd_nonblock(resolve->fds[RESPONSE_RECV_FD], true);
 
-        return resolve;
+        *ret = resolve;
+        return 0;
 
 fail:
         if (resolve)
-                sd_resolve_free(resolve);
+                sd_resolve_unref(resolve);
 
-        return NULL;
+        return r;
 }
 
-_public_ void sd_resolve_free(sd_resolve *resolve) {
-        int i;
-        int saved_errno = errno;
-        unsigned p;
+_public_ sd_resolve* sd_resolve_unref(sd_resolve *resolve) {
+        PROTECT_ERRNO;
 
-        assert(resolve);
+        unsigned i;
 
-        resolve->dead = 1;
+        assert_return(resolve, NULL);
+        assert_return(!resolve_pid_changed(resolve), NULL);
+
+        resolve->dead = true;
 
         if (resolve->fds[REQUEST_SEND_FD] >= 0) {
-                RHeader req = {};
 
-                req.type = REQUEST_TERMINATE;
-                req.length = sizeof(req);
-                req.id = 0;
+                RHeader req = {
+                        .type = REQUEST_TERMINATE,
+                        .length = sizeof(req)
+                };
 
                 /* Send one termination packet for each worker */
-                for (p = 0; p < resolve->valid_workers; p++)
+                for (i = 0; i < resolve->n_valid_workers; i++)
                         send(resolve->fds[REQUEST_SEND_FD], &req, req.length, MSG_NOSIGNAL);
         }
 
         /* Now terminate them and wait until they are gone. */
-        for (p = 0; p < resolve->valid_workers; p++) {
+        for (i = 0; i < resolve->n_valid_workers; i++) {
                 for (;;) {
-                        if (pthread_join(resolve->workers[p], NULL) != EINTR)
+                        if (pthread_join(resolve->workers[i], NULL) != EINTR)
                                 break;
                 }
         }
 
         /* Close all communication channels */
-        for (i = 0; i < MESSAGE_FD_MAX; i++)
+        for (i = 0; i < _FD_MAX; i++)
                 if (resolve->fds[i] >= 0)
-                        close(resolve->fds[i]);
+                        close_nointr_nofail(resolve->fds[i]);
 
-        for (p = 0; p < MAX_QUERIES; p++)
-                if (resolve->queries[p])
-                        sd_resolve_cancel(resolve, resolve->queries[p]);
+        for (i = 0; i < QUERIES_MAX && resolve->n_queries > 0; i++)
+                if (resolve->queries[i])
+                        sd_resolve_cancel(resolve->queries[i]);
 
         free(resolve);
-
-        errno = saved_errno;
+        return NULL;
 }
 
-_public_ int sd_resolve_fd(sd_resolve *resolve) {
-        assert(resolve);
+_public_ int sd_resolve_get_fd(sd_resolve *resolve) {
+        assert_return(resolve, -EINVAL);
+        assert_return(!resolve_pid_changed(resolve), -ECHILD);
 
         return resolve->fds[RESPONSE_RECV_FD];
 }
 
+_public_ int sd_resolve_get_events(sd_resolve *resolve) {
+        assert_return(resolve, -EINVAL);
+        assert_return(!resolve_pid_changed(resolve), -ECHILD);
+
+        return resolve->n_queries > resolve->n_done ? POLLIN : 0;
+}
+
+_public_ int sd_resolve_get_timeout(sd_resolve *resolve, uint64_t *usec) {
+        assert_return(resolve, -EINVAL);
+        assert_return(usec, -EINVAL);
+        assert_return(!resolve_pid_changed(resolve), -ECHILD);
+
+        *usec = (uint64_t) -1;
+        return 0;
+}
+
 static sd_resolve_query *lookup_query(sd_resolve *resolve, unsigned id) {
         sd_resolve_query *q;
+
         assert(resolve);
 
-        q = resolve->queries[id % MAX_QUERIES];
+        q = resolve->queries[id % QUERIES_MAX];
         if (q)
                 if (q->id == id)
                         return q;
@@ -529,52 +640,37 @@ static sd_resolve_query *lookup_query(sd_resolve *resolve, unsigned id) {
         return NULL;
 }
 
-static void complete_query(sd_resolve *resolve, sd_resolve_query *q) {
-        assert(resolve);
+static void complete_query(sd_resolve_query *q) {
         assert(q);
         assert(!q->done);
 
-        q->done = 1;
-
-        if ((q->done_prev = resolve->done_tail))
-                resolve->done_tail->done_next = q;
-        else
-                resolve->done_head = q;
-
-        resolve->done_tail = q;
-        q->done_next = NULL;
+        q->done = true;
+        LIST_PREPEND(done, q->resolve->done, q);
+        q->resolve->n_done ++;
 }
 
-static const void *unserialize_addrinfo(const void *p, struct addrinfo **ret_ai, size_t *length) {
+static int unserialize_addrinfo(const void **p, size_t *length, struct addrinfo **ret_ai) {
         AddrInfoSerialization s;
         size_t l;
         struct addrinfo *ai;
+
         assert(p);
+        assert(*p);
         assert(ret_ai);
         assert(length);
 
         if (*length < sizeof(AddrInfoSerialization))
-                return NULL;
+                return -EBADMSG;
 
-        memcpy(&s, p, sizeof(s));
+        memcpy(&s, *p, sizeof(s));
 
         l = sizeof(AddrInfoSerialization) + s.ai_addrlen + s.canonname_len;
         if (*length < l)
-                return NULL;
+                return -EBADMSG;
 
-        ai = new(struct addrinfo, 1);
+        ai = new0(struct addrinfo, 1);
         if (!ai)
-                goto fail;
-
-        ai->ai_addr = NULL;
-        ai->ai_canonname = NULL;
-        ai->ai_next = NULL;
-
-        if (s.ai_addrlen && !(ai->ai_addr = malloc(s.ai_addrlen)))
-                goto fail;
-
-        if (s.canonname_len && !(ai->ai_canonname = malloc(s.canonname_len)))
-                goto fail;
+                return -ENOMEM;
 
         ai->ai_flags = s.ai_flags;
         ai->ai_family = s.ai_family;
@@ -582,28 +678,34 @@ static const void *unserialize_addrinfo(const void *p, struct addrinfo **ret_ai,
         ai->ai_protocol = s.ai_protocol;
         ai->ai_addrlen = s.ai_addrlen;
 
-        if (ai->ai_addr)
-                memcpy(ai->ai_addr, (const uint8_t*) p + sizeof(AddrInfoSerialization), s.ai_addrlen);
+        if (s.ai_addrlen > 0) {
+                ai->ai_addr = memdup((const uint8_t*) *p + sizeof(AddrInfoSerialization), s.ai_addrlen);
+                if (!ai->ai_addr) {
+                        free(ai);
+                        return -ENOMEM;
+                }
+        }
 
-        if (ai->ai_canonname)
-                memcpy(ai->ai_canonname, (const uint8_t*) p + sizeof(AddrInfoSerialization) + s.ai_addrlen, s.canonname_len);
+        if (s.canonname_len > 0) {
+                ai->ai_canonname = memdup((const uint8_t*) *p + sizeof(AddrInfoSerialization) + s.ai_addrlen, s.canonname_len);
+                if (!ai->ai_canonname) {
+                        free(ai->ai_addr);
+                        free(ai);
+                        return -ENOMEM;
+                }
+        }
 
         *length -= l;
         *ret_ai = ai;
+        *p = ((const uint8_t*) *p) + l;
 
-        return (const uint8_t*) p + l;
-
-
-fail:
-        if (ai)
-                sd_resolve_freeaddrinfo(ai);
-
-        return NULL;
+        return 0;
 }
 
 static int handle_response(sd_resolve *resolve, const Packet *packet, size_t length) {
         const RHeader *resp;
         sd_resolve_query *q;
+        int r;
 
         assert(resolve);
 
@@ -613,7 +715,7 @@ static int handle_response(sd_resolve *resolve, const Packet *packet, size_t len
         assert(length == resp->length);
 
         if (resp->type == RESPONSE_DIED) {
-                resolve->dead = 1;
+                resolve->dead = true;
                 return 0;
         }
 
@@ -622,6 +724,7 @@ static int handle_response(sd_resolve *resolve, const Packet *packet, size_t len
                 return 0;
 
         switch (resp->type) {
+
         case RESPONSE_ADDRINFO: {
                 const AddrInfoResponse *ai_resp = &packet->addrinfo_response;
                 const void *p;
@@ -634,15 +737,20 @@ static int handle_response(sd_resolve *resolve, const Packet *packet, size_t len
                 q->ret = ai_resp->ret;
                 q->_errno = ai_resp->_errno;
                 q->_h_errno = ai_resp->_h_errno;
+
                 l = length - sizeof(AddrInfoResponse);
                 p = (const uint8_t*) resp + sizeof(AddrInfoResponse);
 
                 while (l > 0 && p) {
                         struct addrinfo *ai = NULL;
-                        p = unserialize_addrinfo(p, &ai, &l);
 
-                        if (!p || !ai) {
-                                q->ret = EAI_MEMORY;
+                        r = unserialize_addrinfo(&p, &l, &ai);
+                        if (r < 0) {
+                                q->ret = EAI_SYSTEM;
+                                q->_errno = -r;
+                                q->_h_errno = 0;
+                                freeaddrinfo(q->addrinfo);
+                                q->addrinfo = NULL;
                                 break;
                         }
 
@@ -654,7 +762,7 @@ static int handle_response(sd_resolve *resolve, const Packet *packet, size_t len
                         prev = ai;
                 }
 
-                complete_query(resolve, q);
+                complete_query(q);
                 break;
         }
 
@@ -668,15 +776,25 @@ static int handle_response(sd_resolve *resolve, const Packet *packet, size_t len
                 q->_errno = ni_resp->_errno;
                 q->_h_errno = ni_resp->_h_errno;
 
-                if (ni_resp->hostlen)
-                        if (!(q->host = strndup((const char*) ni_resp + sizeof(NameInfoResponse), ni_resp->hostlen-1)))
+                if (ni_resp->hostlen > 0) {
+                        q->host = strndup((const char*) ni_resp + sizeof(NameInfoResponse), ni_resp->hostlen-1);
+                        if (!q->host) {
                                 q->ret = EAI_MEMORY;
+                                q->_errno = ENOMEM;
+                                q->_h_errno = 0;
+                        }
+                }
 
-                if (ni_resp->servlen)
-                        if (!(q->serv = strndup((const char*) ni_resp + sizeof(NameInfoResponse) + ni_resp->hostlen, ni_resp->servlen-1)))
+                if (ni_resp->servlen > 0) {
+                        q->serv = strndup((const char*) ni_resp + sizeof(NameInfoResponse) + ni_resp->hostlen, ni_resp->servlen-1);
+                        if (!q->serv) {
                                 q->ret = EAI_MEMORY;
+                                q->_errno = ENOMEM;
+                                q->_h_errno = 0;
+                        }
+                }
 
-                complete_query(resolve, q);
+                complete_query(q);
                 break;
         }
 
@@ -691,14 +809,15 @@ static int handle_response(sd_resolve *resolve, const Packet *packet, size_t len
                 q->_h_errno = res_resp->_h_errno;
 
                 if (res_resp->ret >= 0)  {
-                        if (!(q->serv = malloc(res_resp->ret))) {
+                        q->serv = memdup((const char *)resp + sizeof(ResResponse), res_resp->ret);
+                        if (!q->serv) {
                                 q->ret = -1;
                                 q->_errno = ENOMEM;
-                        } else
-                                memcpy(q->serv, (const char *)resp + sizeof(ResResponse), res_resp->ret);
+                                q->_h_errno = 0;
+                        }
                 }
 
-                complete_query(resolve, q);
+                complete_query(q);
                 break;
         }
 
@@ -709,224 +828,245 @@ static int handle_response(sd_resolve *resolve, const Packet *packet, size_t len
         return 0;
 }
 
-_public_ int sd_resolve_wait(sd_resolve *resolve, int block) {
-        int handled = 0;
-        assert(resolve);
+_public_ int sd_resolve_process(sd_resolve *resolve) {
+        int n_processed = 0, r;
+
+        assert_return(resolve, -EINVAL);
+        assert_return(!resolve_pid_changed(resolve), -ECHILD);
 
         for (;;) {
-                Packet buf[BUFSIZE/sizeof(Packet) + 1];
                 ssize_t l;
+                union {
+                        Packet packet;
+                        uint8_t space[BUFSIZE];
+                } buf;
 
-                if (resolve->dead) {
-                        errno = ECHILD;
-                        return -1;
+                l = recv(resolve->fds[RESPONSE_RECV_FD], &buf, sizeof(buf), 0);
+                if (l < 0) {
+                        if (errno == EAGAIN)
+                                return n_processed;
+
+                        return -errno;
                 }
+                if (l == 0)
+                        return -ECONNREFUSED;
 
-                l = recv(resolve->fds[RESPONSE_RECV_FD], buf, sizeof(buf), 0);
-                if (l < 0) {
-                        fd_set fds;
+                r = handle_response(resolve, &buf.packet, (size_t) l);
+                if (r < 0)
+                        return r;
 
-                        if (errno != EAGAIN)
-                                return -1;
+                n_processed++;
+        }
+}
 
-                        if (!block || handled)
-                                return 0;
+_public_ int sd_resolve_wait(sd_resolve *resolve, uint64_t timeout_usec) {
+        int r;
 
-                        FD_ZERO(&fds);
-                        FD_SET(resolve->fds[RESPONSE_RECV_FD], &fds);
+        assert_return(resolve, -EINVAL);
+        assert_return(!resolve_pid_changed(resolve), -ECHILD);
 
-                        if (select(resolve->fds[RESPONSE_RECV_FD]+1, &fds, NULL, NULL, NULL) < 0)
-                                return -1;
+        if (resolve->n_queries <= 0)
+                return 0;
 
-                        continue;
-                }
+        do {
+                r = fd_wait_for_event(resolve->fds[RESPONSE_RECV_FD], POLLIN, timeout_usec);
+        } while (r == -EINTR);
 
-                if (handle_response(resolve, buf, (size_t) l) < 0)
-                        return -1;
+        if (r < 0)
+                return r;
 
-                handled = 1;
-        }
+        return sd_resolve_process(resolve);
 }
 
-static sd_resolve_query *alloc_query(sd_resolve *resolve) {
+static int alloc_query(sd_resolve *resolve, sd_resolve_query **_q) {
         sd_resolve_query *q;
+        int r;
+
         assert(resolve);
+        assert(_q);
 
-        if (resolve->n_queries >= MAX_QUERIES) {
-                errno = ENOMEM;
-                return NULL;
-        }
+        if (resolve->n_queries >= QUERIES_MAX)
+                return -ENOBUFS;
+
+        r = start_threads(resolve, 1);
+        if (r < 0)
+                return r;
 
         while (resolve->queries[resolve->current_index]) {
                 resolve->current_index++;
                 resolve->current_id++;
 
-                while (resolve->current_index >= MAX_QUERIES)
-                        resolve->current_index -= MAX_QUERIES;
+                resolve->current_index %= QUERIES_MAX;
         }
 
-        q = resolve->queries[resolve->current_index] = new(sd_resolve_query, 1);
-        if (!q) {
-                errno = ENOMEM;
-                return NULL;
-        }
+        q = resolve->queries[resolve->current_index] = new0(sd_resolve_query, 1);
+        if (!q)
+                return -ENOMEM;
 
         resolve->n_queries++;
 
         q->resolve = resolve;
-        q->done = 0;
         q->id = resolve->current_id;
-        q->done_next = q->done_prev = NULL;
-        q->ret = 0;
-        q->_errno = 0;
-        q->_h_errno = 0;
-        q->addrinfo = NULL;
-        q->userdata = NULL;
-        q->host = q->serv = NULL;
-
-        return q;
+
+        *_q = q;
+        return 0;
 }
 
-_public_ sd_resolve_query* sd_resolve_getaddrinfo(sd_resolve *resolve, const char *node, const char *service, const struct addrinfo *hints) {
-        AddrInfoRequest data[BUFSIZE/sizeof(AddrInfoRequest) + 1] = {};
-        AddrInfoRequest *req = data;
+_public_ int sd_resolve_getaddrinfo(
+                sd_resolve *resolve,
+                const char *node,
+                const char *service,
+                const struct addrinfo *hints,
+                sd_resolve_query **_q) {
+
+        AddrInfoRequest req = {};
+        struct msghdr mh = {};
+        struct iovec iov[3];
         sd_resolve_query *q;
-        assert(resolve);
-        assert(node || service);
+        int r;
 
-        if (resolve->dead) {
-                errno = ECHILD;
-                return NULL;
-        }
+        assert_return(resolve, -EINVAL);
+        assert_return(node || service, -EINVAL);
+        assert_return(_q, -EINVAL);
+        assert_return(!resolve_pid_changed(resolve), -ECHILD);
 
-        q = alloc_query(resolve);
-        if (!q)
-                return NULL;
+        r = alloc_query(resolve, &q);
+        if (r < 0)
+                return r;
 
-        req->node_len = node ? strlen(node)+1 : 0;
-        req->service_len = service ? strlen(service)+1 : 0;
+        req.node_len = node ? strlen(node)+1 : 0;
+        req.service_len = service ? strlen(service)+1 : 0;
 
-        req->header.id = q->id;
-        req->header.type = q->type = REQUEST_ADDRINFO;
-        req->header.length = sizeof(AddrInfoRequest) + req->node_len + req->service_len;
+        req.header.id = q->id;
+        req.header.type = q->type = REQUEST_ADDRINFO;
+        req.header.length = sizeof(AddrInfoRequest) + req.node_len + req.service_len;
 
-        if (req->header.length > BUFSIZE) {
-                errno = ENOMEM;
-                goto fail;
+        if (hints) {
+                req.hints_valid = true;
+                req.ai_flags = hints->ai_flags;
+                req.ai_family = hints->ai_family;
+                req.ai_socktype = hints->ai_socktype;
+                req.ai_protocol = hints->ai_protocol;
         }
 
-        if (!(req->hints_is_null = !hints)) {
-                req->ai_flags = hints->ai_flags;
-                req->ai_family = hints->ai_family;
-                req->ai_socktype = hints->ai_socktype;
-                req->ai_protocol = hints->ai_protocol;
-        }
+        iov[mh.msg_iovlen++] = (struct iovec) { .iov_base = &req, .iov_len = sizeof(AddrInfoRequest) };
 
         if (node)
-                strcpy((char*) req + sizeof(AddrInfoRequest), node);
+                iov[mh.msg_iovlen++] = (struct iovec) { .iov_base = (void*) node, .iov_len = req.node_len };
 
         if (service)
-                strcpy((char*) req + sizeof(AddrInfoRequest) + req->node_len, service);
+                iov[mh.msg_iovlen++] = (struct iovec) { .iov_base = (void*) service, .iov_len = req.service_len };
 
-        if (send(resolve->fds[REQUEST_SEND_FD], req, req->header.length, MSG_NOSIGNAL) < 0)
-                goto fail;
-
-        return q;
+        mh.msg_iov = iov;
 
-fail:
-        if (q)
-                sd_resolve_cancel(resolve, q);
+        if (sendmsg(resolve->fds[REQUEST_SEND_FD], &mh, MSG_NOSIGNAL) < 0) {
+                sd_resolve_cancel(q);
+                return -errno;
+        }
 
-        return NULL;
+        *_q = q;
+        return 0;
 }
 
-_public_ int sd_resolve_getaddrinfo_done(sd_resolve *resolve, sd_resolve_query* q, struct addrinfo **ret_res) {
+_public_ int sd_resolve_getaddrinfo_done(sd_resolve_query* q, struct addrinfo **ret_res) {
         int ret;
-        assert(resolve);
-        assert(q);
-        assert(q->resolve == resolve);
-        assert(q->type == REQUEST_ADDRINFO);
 
-        if (resolve->dead) {
-                errno = ECHILD;
+        if (!q) {
+                errno = EINVAL;
                 return EAI_SYSTEM;
         }
 
+        if (q->type != REQUEST_ADDRINFO) {
+                errno = ENOTTY;
+                return EAI_SYSTEM;
+        }
+
+        if (resolve_pid_changed(q->resolve)) {
+                errno = ECHILD;
+                return EAI_SYSTEM;
+        }
         if (!q->done)
                 return EAI_AGAIN;
 
-        *ret_res = q->addrinfo;
-        q->addrinfo = NULL;
+        if (ret_res) {
+                *ret_res = q->addrinfo;
+                q->addrinfo = NULL;
+        }
 
         ret = q->ret;
 
-        if (ret == EAI_SYSTEM)
+        if (ret != 0) {
                 errno = q->_errno;
-
-        if (ret != 0)
                 h_errno = q->_h_errno;
+        }
 
-        sd_resolve_cancel(resolve, q);
+        sd_resolve_cancel(q);
 
         return ret;
 }
 
-_public_ sd_resolve_query* sd_resolve_getnameinfo(sd_resolve *resolve, const struct sockaddr *sa, socklen_t salen, int flags, int gethost, int getserv) {
-        NameInfoRequest data[BUFSIZE/sizeof(NameInfoRequest) + 1] = {};
-        NameInfoRequest *req = data;
-        sd_resolve_query *q;
-
-        assert(resolve);
-        assert(sa);
-        assert(salen > 0);
+_public_ int sd_resolve_getnameinfo(
+                sd_resolve *resolve,
+                const struct sockaddr *sa, socklen_t salen,
+                int flags,
+                int gethost, int getserv,
+                sd_resolve_query**_q) {
 
-        if (resolve->dead) {
-                errno = ECHILD;
-                return NULL;
-        }
-
-        q = alloc_query(resolve);
-        if (!q)
-                return NULL;
+        NameInfoRequest req = {};
+        struct msghdr mh = {};
+        struct iovec iov[2];
+        sd_resolve_query *q;
+        int r;
 
-        req->header.id = q->id;
-        req->header.type = q->type = REQUEST_NAMEINFO;
-        req->header.length = sizeof(NameInfoRequest) + salen;
+        assert_return(resolve, -EINVAL);
+        assert_return(sa, -EINVAL);
+        assert_return(salen >= sizeof(struct sockaddr), -EINVAL);
+        assert_return(salen <= sizeof(union sockaddr_union), -EINVAL);
+        assert_return(_q, -EINVAL);
+        assert_return(!resolve_pid_changed(resolve), -ECHILD);
 
-        if (req->header.length > BUFSIZE) {
-                errno = ENOMEM;
-                goto fail;
-        }
+        r = alloc_query(resolve, &q);
+        if (r < 0)
+                return r;
 
-        req->flags = flags;
-        req->sockaddr_len = salen;
-        req->gethost = gethost;
-        req->getserv = getserv;
+        req.header.id = q->id;
+        req.header.type = q->type = REQUEST_NAMEINFO;
+        req.header.length = sizeof(NameInfoRequest) + salen;
 
-        memcpy((uint8_t*) req + sizeof(NameInfoRequest), sa, salen);
+        req.flags = flags;
+        req.sockaddr_len = salen;
+        req.gethost = !!gethost;
+        req.getserv = !!getserv;
 
-        if (send(resolve->fds[REQUEST_SEND_FD], req, req->header.length, MSG_NOSIGNAL) < 0)
-                goto fail;
+        iov[0] = (struct iovec) { .iov_base = &req, .iov_len = sizeof(NameInfoRequest) };
+        iov[1] = (struct iovec) { .iov_base = (void*) sa, .iov_len = salen };
 
-        return q;
+        mh.msg_iov = iov;
+        mh.msg_iovlen = 2;
 
-fail:
-        if (q)
-                sd_resolve_cancel(resolve, q);
+        if (sendmsg(resolve->fds[REQUEST_SEND_FD], &mh, MSG_NOSIGNAL) < 0) {
+                sd_resolve_cancel(q);
+                return -errno;
+        }
 
-        return NULL;
+        *_q = q;
+        return 0;
 }
 
-_public_ int sd_resolve_getnameinfo_done(sd_resolve *resolve, sd_resolve_query* q, char *ret_host, size_t hostlen, char *ret_serv, size_t servlen) {
+_public_ int sd_resolve_getnameinfo_done(sd_resolve_query* q, char **ret_host, char **ret_serv) {
         int ret;
-        assert(resolve);
-        assert(q);
-        assert(q->resolve == resolve);
-        assert(q->type == REQUEST_NAMEINFO);
-        assert(!ret_host || hostlen);
-        assert(!ret_serv || servlen);
 
-        if (resolve->dead) {
+        if (!q) {
+                errno = EINVAL;
+                return EAI_SYSTEM;
+        }
+
+        if (q->type != REQUEST_NAMEINFO) {
+                errno = ENOTTY;
+                return EAI_SYSTEM;
+        }
+
+        if (resolve_pid_changed(q->resolve)) {
                 errno = ECHILD;
                 return EAI_SYSTEM;
         }
@@ -934,163 +1074,154 @@ _public_ int sd_resolve_getnameinfo_done(sd_resolve *resolve, sd_resolve_query*
         if (!q->done)
                 return EAI_AGAIN;
 
-        if (ret_host && q->host) {
-                strncpy(ret_host, q->host, hostlen);
-                ret_host[hostlen-1] = 0;
+        if (ret_host) {
+                *ret_host = q->host;
+                q->host = NULL;
         }
 
-        if (ret_serv && q->serv) {
-                strncpy(ret_serv, q->serv, servlen);
-                ret_serv[servlen-1] = 0;
+        if (ret_serv) {
+                *ret_serv = q->serv;
+                q->serv = NULL;
         }
 
         ret = q->ret;
 
-        if (ret == EAI_SYSTEM)
+        if (ret != 0) {
                 errno = q->_errno;
-
-        if (ret != 0)
                 h_errno = q->_h_errno;
+        }
 
-        sd_resolve_cancel(resolve, q);
+        sd_resolve_cancel(q);
 
         return ret;
 }
 
-static sd_resolve_query * resolve_res(sd_resolve *resolve, QueryType qtype, const char *dname, int class, int type) {
-        ResRequest data[BUFSIZE/sizeof(ResRequest) + 1];
-        ResRequest *req = data;
-        sd_resolve_query *q;
+static int resolve_res(
+                sd_resolve *resolve,
+                QueryType qtype,
+                const char *dname,
+                int class, int type,
+                sd_resolve_query **_q) {
 
-        assert(resolve);
-        assert(dname);
-
-        if (resolve->dead) {
-                errno = ECHILD;
-                return NULL;
-        }
-
-        q = alloc_query(resolve);
-        if (!q)
-                return NULL;
-
-        req->dname_len = strlen(dname) + 1;
+        struct msghdr mh = {};
+        struct iovec iov[2];
+        ResRequest req = {};
+        sd_resolve_query *q;
+        int r;
 
-        req->header.id = q->id;
-        req->header.type = q->type = qtype;
-        req->header.length = sizeof(ResRequest) + req->dname_len;
+        assert_return(resolve, -EINVAL);
+        assert_return(dname, -EINVAL);
+        assert_return(_q, -EINVAL);
+        assert_return(!resolve_pid_changed(resolve), -ECHILD);
 
-        if (req->header.length > BUFSIZE) {
-                errno = ENOMEM;
-                goto fail;
-        }
+        r = alloc_query(resolve, &q);
+        if (r < 0)
+                return r;
 
-        req->class = class;
-        req->type = type;
+        req.dname_len = strlen(dname) + 1;
+        req.class = class;
+        req.type = type;
 
-        strcpy((char*) req + sizeof(ResRequest), dname);
+        req.header.id = q->id;
+        req.header.type = q->type = qtype;
+        req.header.length = sizeof(ResRequest) + req.dname_len;
 
-        if (send(resolve->fds[REQUEST_SEND_FD], req, req->header.length, MSG_NOSIGNAL) < 0)
-                goto fail;
+        iov[0] = (struct iovec) { .iov_base = &req, .iov_len = sizeof(ResRequest) };
+        iov[1] = (struct iovec) { .iov_base = (void*) dname, .iov_len = req.dname_len };
 
-        return q;
+        mh.msg_iov = iov;
+        mh.msg_iovlen = 2;
 
-fail:
-        if (q)
-                sd_resolve_cancel(resolve, q);
+        if (sendmsg(resolve->fds[REQUEST_SEND_FD], &mh, MSG_NOSIGNAL) < 0) {
+                sd_resolve_cancel(q);
+                return -errno;
+        }
 
-        return NULL;
+        *_q = q;
+        return 0;
 }
 
-_public_ sd_resolve_query* sd_resolve_res_query(sd_resolve *resolve, const char *dname, int class, int type) {
-        return resolve_res(resolve, REQUEST_RES_QUERY, dname, class, type);
+_public_ int sd_resolve_res_query(sd_resolve *resolve, const char *dname, int class, int type, sd_resolve_query** q) {
+        return resolve_res(resolve, REQUEST_RES_QUERY, dname, class, type, q);
 }
 
-_public_ sd_resolve_query* sd_resolve_res_search(sd_resolve *resolve, const char *dname, int class, int type) {
-        return resolve_res(resolve, REQUEST_RES_SEARCH, dname, class, type);
+_public_ int sd_resolve_res_search(sd_resolve *resolve, const char *dname, int class, int type, sd_resolve_query** q) {
+        return resolve_res(resolve, REQUEST_RES_SEARCH, dname, class, type, q);
 }
 
-_public_ int sd_resolve_res_done(sd_resolve *resolve, sd_resolve_query* q, unsigned char **answer) {
+_public_ int sd_resolve_res_done(sd_resolve_query* q, unsigned char **answer) {
         int ret;
-        assert(resolve);
-        assert(q);
-        assert(q->resolve == resolve);
-        assert(q->type == REQUEST_RES_QUERY || q->type == REQUEST_RES_SEARCH);
-        assert(answer);
 
-        if (resolve->dead) {
-                errno = ECHILD;
-                return -ECHILD;
-        }
+        assert_return(q, -EINVAL);
+        assert_return(answer, -EINVAL);
+        assert_return(q->type == REQUEST_RES_QUERY || q->type == REQUEST_RES_SEARCH, -ENOTTY);
+        assert_return(!resolve_pid_changed(q->resolve), -ECHILD);
 
-        if (!q->done) {
-                errno = EAGAIN;
+        if (!q->done)
                 return -EAGAIN;
-        }
 
-        *answer = (unsigned char *)q->serv;
+        *answer = (unsigned char *) q->serv;
         q->serv = NULL;
 
         ret = q->ret;
 
-        if (ret < 0) {
+        if (ret != 0) {
                 errno = q->_errno;
                 h_errno = q->_h_errno;
         }
 
-        sd_resolve_cancel(resolve, q);
+        sd_resolve_cancel(q);
 
         return ret < 0 ? -errno : ret;
 }
 
-_public_ sd_resolve_query* sd_resolve_get_next(sd_resolve *resolve) {
-        assert(resolve);
-        return resolve->done_head;
+_public_ int sd_resolve_get_next(sd_resolve *resolve, sd_resolve_query **q) {
+        assert_return(resolve, -EINVAL);
+        assert_return(q, -EINVAL);
+        assert_return(!resolve_pid_changed(resolve), -ECHILD);
+
+        *q = resolve->done;
+        return !!resolve->done;
 }
 
 _public_ int sd_resolve_get_n_queries(sd_resolve *resolve) {
-        assert(resolve);
+        assert_return(resolve, -EINVAL);
+        assert_return(!resolve_pid_changed(resolve), -ECHILD);
+
         return resolve->n_queries;
 }
 
-_public_ void sd_resolve_cancel(sd_resolve *resolve, sd_resolve_query* q) {
+_public_ int sd_resolve_cancel(sd_resolve_query* q) {
+        PROTECT_ERRNO;
         int i;
-        int saved_errno = errno;
 
-        assert(resolve);
-        assert(q);
-        assert(q->resolve == resolve);
-        assert(resolve->n_queries > 0);
+        if (!q)
+                return 0;
 
-        if (q->done) {
+        assert_return(!resolve_pid_changed(q->resolve), -ECHILD);
 
-                if (q->done_prev)
-                        q->done_prev->done_next = q->done_next;
-                else
-                        resolve->done_head = q->done_next;
+        assert(q->resolve);
+        assert(q->resolve->n_queries > 0);
 
-                if (q->done_next)
-                        q->done_next->done_prev = q->done_prev;
-                else
-                        resolve->done_tail = q->done_prev;
+        if (q->done) {
+                LIST_REMOVE(done, q->resolve->done, q);
+                q->resolve->n_done--;
         }
 
-        i = q->id % MAX_QUERIES;
-        assert(resolve->queries[i] == q);
-        resolve->queries[i] = NULL;
+        i = q->id % QUERIES_MAX;
+        assert(q->resolve->queries[i] == q);
+        q->resolve->queries[i] = NULL;
+        q->resolve->n_queries--;
 
         sd_resolve_freeaddrinfo(q->addrinfo);
         free(q->host);
         free(q->serv);
-
-        resolve->n_queries--;
         free(q);
 
-        errno = saved_errno;
+        return 0;
 }
 
 _public_ void sd_resolve_freeaddrinfo(struct addrinfo *ai) {
-        int saved_errno = errno;
 
         while (ai) {
                 struct addrinfo *next = ai->ai_next;
@@ -1101,30 +1232,30 @@ _public_ void sd_resolve_freeaddrinfo(struct addrinfo *ai) {
 
                 ai = next;
         }
-
-        errno = saved_errno;
 }
 
-_public_ int sd_resolve_isdone(sd_resolve *resolve, sd_resolve_query*q) {
-        assert(resolve);
-        assert(q);
-        assert(q->resolve == resolve);
+_public_ int sd_resolve_is_done(sd_resolve_query *q) {
+        assert_return(q, -EINVAL);
+        assert_return(!resolve_pid_changed(q->resolve), -ECHILD);
 
         return q->done;
 }
 
-_public_ void sd_resolve_setuserdata(sd_resolve *resolve, sd_resolve_query *q, void *userdata) {
-        assert(q);
-        assert(resolve);
-        assert(q->resolve = resolve);
+_public_ void* sd_resolve_set_userdata(sd_resolve_query *q, void *userdata) {
+        void *ret;
 
+        assert_return(q, NULL);
+        assert_return(!resolve_pid_changed(q->resolve), NULL);
+
+        ret = q->userdata;
         q->userdata = userdata;
+
+        return ret;
 }
 
-_public_ void* sd_resolve_getuserdata(sd_resolve *resolve, sd_resolve_query *q) {
-        assert(q);
-        assert(resolve);
-        assert(q->resolve = resolve);
+_public_ void* sd_resolve_get_userdata(sd_resolve_query *q) {
+        assert_return(q, NULL);
+        assert_return(!resolve_pid_changed(q->resolve), NULL);
 
         return q->userdata;
 }