r4916: added "host" name resolution using fork() per gethostbyname()

comments welcome, but please think about the alternatives first :-)

source/libcli/config.mk

@@ -32,7 +32,8 @@ ADD_OBJ_FILES = \
 	libcli/resolve/resolve.o \
 	libcli/resolve/nbtlist.o \
 	libcli/resolve/bcast.o \
-	libcli/resolve/wins.o
+	libcli/resolve/wins.o \
+	libcli/resolve/host.o
 REQUIRED_SUBSYSTEMS = LIBCLI_NBT
 
 [SUBSYSTEM::LIBCLI]

source/libcli/resolve/host.c

@@ -0,0 +1,233 @@
+/* 
+   Unix SMB/CIFS implementation.
+
+   async gethostbyname() name resolution module
+
+   Copyright (C) Andrew Tridgell 2005
+   
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2 of the License, or
+   (at your option) any later version.
+   
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+   
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+*/
+
+/*
+  this module uses a fork() per gethostbyname() call. At first that
+  might seem crazy, but it is actually very fast, and solves many of
+  the tricky problems of keeping a child hanging around in a library
+  (like what happens when the parent forks). We use a talloc
+  destructor to ensure that the child is cleaned up when we have
+  finished with this name resolution.
+*/
+
+#include "includes.h"
+#include "events.h"
+#include "system/network.h"
+#include "libcli/raw/libcliraw.h"
+#include "libcli/composite/composite.h"
+
+struct host_state {
+	struct nbt_name name;
+	const char *reply_addr;
+	pid_t child;
+	int child_fd;
+	struct fd_event *fde;
+	struct event_context *event_ctx;
+};
+
+
+/*
+  kill off a wayward child if needed. This allows us to stop an async
+  name resolution without leaving a potentially blocking call running
+  in a child
+*/
+static int host_destructor(void *ptr)
+{
+	struct host_state *state = talloc_get_type(ptr, struct host_state);
+	close(state->child_fd);
+	if (state->child != (pid_t)-1) {
+		kill(state->child, SIGTERM);
+	}
+	if (state->fde) {
+		event_remove_fd(state->event_ctx, state->fde);
+	}
+	return 0;
+}
+
+/*
+  the blocking child
+*/
+static void run_child(struct smbcli_composite *c, int fd)
+{
+	struct host_state *state = talloc_get_type(c->private, struct host_state);
+	struct ipv4_addr ip;
+	const char *address;
+
+	/* this is the blocking call we are going to lots of trouble
+	   to avoid in the parent */
+	ip = interpret_addr2(state->name.name);
+
+	address = sys_inet_ntoa(ip);
+	if (address != NULL) {
+		write(fd, address, strlen(address)+1);
+	}
+}
+
+/*
+  handle a read event on the pipe
+*/
+static void pipe_handler(struct event_context *ev, struct fd_event *fde, 
+			 struct timeval t, uint16_t flags)
+{
+	struct smbcli_composite *c = talloc_get_type(fde->private, struct smbcli_composite);
+	struct host_state *state = talloc_get_type(c->private, struct host_state);
+	char address[128];
+	int ret;
+
+	/* if we get any event from the child then we know that we
+	   won't need to kill it off */
+	state->child = (pid_t)-1;
+
+	/* yes, we don't care about EAGAIN or other niceities
+	   here. They just can't happen with this parent/child
+	   relationship, and even if they did then giving an error is
+	   the right thing to do */
+	ret = read(state->child_fd, address, sizeof(address)-1);
+	if (ret <= 0) goto failed;
+
+	/* enusre the address looks good */
+	address[ret] = 0;
+	if (strcmp(address, "0.0.0.0") == 0 ||
+	    sys_inet_addr(address) == INADDR_NONE) {
+		goto failed;
+	}
+
+	state->reply_addr = talloc_strdup(state, address);
+	if (state->reply_addr == NULL) goto failed;
+
+	c->status = NT_STATUS_OK;
+	c->state = SMBCLI_REQUEST_DONE;
+	if (c->async.fn) {
+		c->async.fn(c);
+	}
+	return;
+
+failed:
+	c->status = NT_STATUS_BAD_NETWORK_NAME;
+	c->state = SMBCLI_REQUEST_ERROR;
+	if (c->async.fn) {
+		c->async.fn(c);
+	}
+}
+
+/*
+  gethostbyname name resolution method - async send
+ */
+struct smbcli_composite *resolve_name_host_send(struct nbt_name *name, 
+						struct event_context *event_ctx)
+{
+	struct smbcli_composite *c;
+	struct host_state *state;
+	NTSTATUS status;
+	int fd[2] = { -1, -1 };
+	struct fd_event fde;
+	int ret;
+
+	c = talloc_zero(NULL, struct smbcli_composite);
+	if (c == NULL) goto failed;
+
+	state = talloc(c, struct host_state);
+	if (state == NULL) goto failed;
+
+	status = nbt_name_dup(state, name, &state->name);
+	if (!NT_STATUS_IS_OK(status)) goto failed;
+
+	c->state = SMBCLI_REQUEST_SEND;
+	c->private = state;
+	c->event_ctx = talloc_reference(c, event_ctx);
+
+	/* setup a pipe to chat to our child */
+	ret = pipe(fd);
+	if (ret == -1) goto failed;
+
+	state->child_fd = fd[0];
+	state->event_ctx = c->event_ctx;
+
+	/* we need to put the child in our event context so
+	   we know when the gethostbyname() has finished */
+	fde.fd = state->child_fd;
+	fde.flags = EVENT_FD_READ;
+	fde.handler = pipe_handler;
+	fde.private = c;
+	state->fde = event_add_fd(c->event_ctx, &fde);
+	if (state->fde == NULL) {
+		close(fd[0]);
+		close(fd[1]);
+		goto failed;
+	}
+
+	/* signal handling in posix really sucks - doing this in a library
+	   affects the whole app, but what else to do?? */
+	signal(SIGCHLD, SIG_IGN);
+
+	state->child = fork();
+	if (state->child == (pid_t)-1) {
+		goto failed;
+	}
+
+	if (state->child == 0) {
+		close(fd[0]);
+		run_child(c, fd[1]);
+		_exit(0);
+	}
+	close(fd[1]);
+
+	/* cleanup wayward children */
+	talloc_set_destructor(state, host_destructor);
+
+	return c;	
+
+failed:
+	talloc_free(c);
+	return NULL;
+}
+
+/*
+  gethostbyname name resolution method - recv side
+*/
+NTSTATUS resolve_name_host_recv(struct smbcli_composite *c, 
+				 TALLOC_CTX *mem_ctx, const char **reply_addr)
+{
+	NTSTATUS status;
+
+	status = smb_composite_wait(c);
+
+	if (NT_STATUS_IS_OK(status)) {
+		struct host_state *state = talloc_get_type(c->private, struct host_state);
+		*reply_addr = talloc_steal(mem_ctx, state->reply_addr);
+	}
+
+	talloc_free(c);
+	return status;
+}
+
+/*
+  gethostbyname name resolution method - sync call
+ */
+NTSTATUS resolve_name_host(struct nbt_name *name, 
+			    TALLOC_CTX *mem_ctx,
+			    const char **reply_addr)
+{
+	struct smbcli_composite *c = resolve_name_host_send(name, NULL);
+	return resolve_name_host_recv(c, mem_ctx, reply_addr);
+}
+

source/libcli/resolve/resolve.c

@@ -33,6 +33,33 @@ struct resolve_state {
 
 static struct smbcli_composite *setup_next_method(struct smbcli_composite *c);
 
+/* pointers to the resolver backends */
+static const struct resolve_method {
+	const char *name;
+	struct smbcli_composite *(*send_fn)(struct nbt_name *, struct event_context *);
+	NTSTATUS (*recv_fn)(struct smbcli_composite *, TALLOC_CTX *, const char **);
+} methods[] = {
+	{ "bcast", resolve_name_bcast_send, resolve_name_bcast_recv },
+	{ "wins",  resolve_name_wins_send, resolve_name_wins_recv },
+	{ "host",  resolve_name_host_send, resolve_name_host_recv }
+};
+
+
+/* 
+   find a matching backend
+*/
+static const struct resolve_method *find_method(const char *name)
+{
+	int i;
+	if (name == NULL) return NULL;
+	for (i=0;i<ARRAY_SIZE(methods);i++) {
+		if (strcasecmp(name, methods[i].name) == 0) {
+			return &methods[i];
+		}
+	}
+	return NULL;
+}
+
 /*
   handle completion of one name resolve method
 */
@@ -40,15 +67,9 @@ static void resolve_handler(struct smbcli_composite *req)
 {
 	struct smbcli_composite *c = req->async.private;
 	struct resolve_state *state = talloc_get_type(c->private, struct resolve_state);
-	const char *method = state->methods[0];
+	const struct resolve_method *method = find_method(state->methods[0]);
 
-	if (strcasecmp(method, "bcast")) {
+	c->status = method->recv_fn(req, state, &state->reply_addr);
-		c->status = resolve_name_bcast_recv(req, state, &state->reply_addr);
-	} else if (strcasecmp(method, "wins")) {
-		c->status = resolve_name_wins_recv(req, state, &state->reply_addr);
-	} else {
-		c->status = NT_STATUS_INTERNAL_ERROR;
-	}
 	
 	if (!NT_STATUS_IS_OK(c->status)) {
 		state->methods++;
@@ -72,18 +93,16 @@ static void resolve_handler(struct smbcli_composite *req)
 static struct smbcli_composite *setup_next_method(struct smbcli_composite *c)
 {
 	struct resolve_state *state = talloc_get_type(c->private, struct resolve_state);
-	const char *method;
 	struct smbcli_composite *req = NULL;
 
 	do {
-		method = state->methods[0];
+		const struct resolve_method *method = find_method(state->methods[0]);
-		if (method == NULL) break;
+		if (method) {
-		if (strcasecmp(method, "bcast")) {
+			req = method->send_fn(&state->name, c->event_ctx);
-			req = resolve_name_bcast_send(&state->name, c->event_ctx);
+			if (req == NULL) {
-		} else if (strcasecmp(method, "wins")) {
+				state->methods++;
-			req = resolve_name_wins_send(&state->name, c->event_ctx);
+			}
 		}
-		if (req == NULL) state->methods++;
 	} while (!req && state->methods[0]);
 
 	if (req) {