Merge branch 'jh/builtin-fsmonitor-part1'

Built-in fsmonitor (part 1).

* jh/builtin-fsmonitor-part1:
  t/helper/simple-ipc: convert test-simple-ipc to use start_bg_command
  run-command: create start_bg_command
  simple-ipc/ipc-win32: add Windows ACL to named pipe
  simple-ipc/ipc-win32: add trace2 debugging
  simple-ipc: move definition of ipc_active_state outside of ifdef
  simple-ipc: preparations for supporting binary messages.
  trace2: add trace2_child_ready() to report on background children

Documentation/technical/api-trace2.txt

@@ -613,6 +613,46 @@ stopping after the waitpid() and includes OS process creation overhead).
 So this time will be slightly larger than the atexit time reported by
 the child process itself.
 
+`"child_ready"`::
+	This event is generated after the current process has started
+	a background process and released all handles to it.
++
+------------
+{
+	"event":"child_ready",
+	...
+	"child_id":2,
+	"pid":14708,	 # child PID
+	"ready":"ready", # child ready state
+	"t_rel":0.110605 # observed run-time of child process
+}
+------------
++
+Note that the session-id of the child process is not available to
+the current/spawning process, so the child's PID is reported here as
+a hint for post-processing.  (But it is only a hint because the child
+process may be a shell script which doesn't have a session-id.)
++
+This event is generated after the child is started in the background
+and given a little time to boot up and start working.  If the child
+startups normally and while the parent is still waiting, the "ready"
+field will have the value "ready".
+If the child is too slow to start and the parent times out, the field
+will have the value "timeout".
+If the child starts but the parent is unable to probe it, the field
+will have the value "error".
++
+After the parent process emits this event, it will release all of its
+handles to the child process and treat the child as a background
+daemon.  So even if the child does eventually finish booting up,
+the parent will not emit an updated event.
++
+Note that the `t_rel` field contains the observed run time in seconds
+when the parent released the child process into the background.
+The child is assumed to be a long-running daemon process and may
+outlive the parent process.  So the parent's child event times should
+not be compared to the child's atexit times.
+
 `"exec"`::
 	This event is generated before git attempts to `exec()`
 	another command rather than starting a child process.

compat/simple-ipc/ipc-unix-socket.c

@@ -168,7 +168,8 @@ void ipc_client_close_connection(struct ipc_client_connection *connection)
 
 int ipc_client_send_command_to_connection(
 	struct ipc_client_connection *connection,
-	const char *message, struct strbuf *answer)
+	const char *message, size_t message_len,
+	struct strbuf *answer)
 {
 	int ret = 0;
 
@@ -176,7 +177,7 @@ int ipc_client_send_command_to_connection(
 
 	trace2_region_enter("ipc-client", "send-command", NULL);
 
-	if (write_packetized_from_buf_no_flush(message, strlen(message),
+	if (write_packetized_from_buf_no_flush(message, message_len,
 					       connection->fd) < 0 ||
 	    packet_flush_gently(connection->fd) < 0) {
 		ret = error(_("could not send IPC command"));
@@ -197,7 +198,8 @@ done:
 
 int ipc_client_send_command(const char *path,
 			    const struct ipc_client_connect_options *options,
-			    const char *message, struct strbuf *answer)
+			    const char *message, size_t message_len,
+			    struct strbuf *answer)
 {
 	int ret = -1;
 	enum ipc_active_state state;
@@ -208,7 +210,9 @@ int ipc_client_send_command(const char *path,
 	if (state != IPC_STATE__LISTENING)
 		return ret;
 
-	ret = ipc_client_send_command_to_connection(connection, message, answer);
+	ret = ipc_client_send_command_to_connection(connection,
+						    message, message_len,
+						    answer);
 
 	ipc_client_close_connection(connection);
 
@@ -503,7 +507,7 @@ static int worker_thread__do_io(
 	if (ret >= 0) {
 		ret = worker_thread_data->server_data->application_cb(
 			worker_thread_data->server_data->application_data,
-			buf.buf, do_io_reply_callback, &reply_data);
+			buf.buf, buf.len, do_io_reply_callback, &reply_data);
 
 		packet_flush_gently(reply_data.fd);
 	}

compat/simple-ipc/ipc-win32.c

@@ -3,6 +3,8 @@
 #include "strbuf.h"
 #include "pkt-line.h"
 #include "thread-utils.h"
+#include "accctrl.h"
+#include "aclapi.h"
 
 #ifndef SUPPORTS_SIMPLE_IPC
 /*
@@ -49,6 +51,9 @@ static enum ipc_active_state get_active_state(wchar_t *pipe_path)
 	if (GetLastError() == ERROR_FILE_NOT_FOUND)
 		return IPC_STATE__PATH_NOT_FOUND;
 
+	trace2_data_intmax("ipc-debug", NULL, "getstate/waitpipe/gle",
+			   (intmax_t)GetLastError());
+
 	return IPC_STATE__OTHER_ERROR;
 }
 
@@ -109,9 +114,15 @@ static enum ipc_active_state connect_to_server(
 			t_start_ms = (DWORD)(getnanotime() / 1000000);
 
 			if (!WaitNamedPipeW(wpath, timeout_ms)) {
-				if (GetLastError() == ERROR_SEM_TIMEOUT)
+				DWORD gleWait = GetLastError();
+
+				if (gleWait == ERROR_SEM_TIMEOUT)
 					return IPC_STATE__NOT_LISTENING;
 
+				trace2_data_intmax("ipc-debug", NULL,
+						   "connect/waitpipe/gle",
+						   (intmax_t)gleWait);
+
 				return IPC_STATE__OTHER_ERROR;
 			}
 
@@ -133,17 +144,31 @@ static enum ipc_active_state connect_to_server(
 			break; /* try again */
 
 		default:
+			trace2_data_intmax("ipc-debug", NULL,
+					   "connect/createfile/gle",
+					   (intmax_t)gle);
+
 			return IPC_STATE__OTHER_ERROR;
 		}
 	}
 
 	if (!SetNamedPipeHandleState(hPipe, &mode, NULL, NULL)) {
+		gle = GetLastError();
+		trace2_data_intmax("ipc-debug", NULL,
+				   "connect/setpipestate/gle",
+				   (intmax_t)gle);
+
 		CloseHandle(hPipe);
 		return IPC_STATE__OTHER_ERROR;
 	}
 
 	*pfd = _open_osfhandle((intptr_t)hPipe, O_RDWR|O_BINARY);
 	if (*pfd < 0) {
+		gle = GetLastError();
+		trace2_data_intmax("ipc-debug", NULL,
+				   "connect/openosfhandle/gle",
+				   (intmax_t)gle);
+
 		CloseHandle(hPipe);
 		return IPC_STATE__OTHER_ERROR;
 	}
@@ -208,7 +233,8 @@ void ipc_client_close_connection(struct ipc_client_connection *connection)
 
 int ipc_client_send_command_to_connection(
 	struct ipc_client_connection *connection,
-	const char *message, struct strbuf *answer)
+	const char *message, size_t message_len,
+	struct strbuf *answer)
 {
 	int ret = 0;
 
@@ -216,7 +242,7 @@ int ipc_client_send_command_to_connection(
 
 	trace2_region_enter("ipc-client", "send-command", NULL);
 
-	if (write_packetized_from_buf_no_flush(message, strlen(message),
+	if (write_packetized_from_buf_no_flush(message, message_len,
 					       connection->fd) < 0 ||
 	    packet_flush_gently(connection->fd) < 0) {
 		ret = error(_("could not send IPC command"));
@@ -239,7 +265,8 @@ done:
 
 int ipc_client_send_command(const char *path,
 			    const struct ipc_client_connect_options *options,
-			    const char *message, struct strbuf *response)
+			    const char *message, size_t message_len,
+			    struct strbuf *response)
 {
 	int ret = -1;
 	enum ipc_active_state state;
@@ -250,7 +277,9 @@ int ipc_client_send_command(const char *path,
 	if (state != IPC_STATE__LISTENING)
 		return ret;
 
-	ret = ipc_client_send_command_to_connection(connection, message, response);
+	ret = ipc_client_send_command_to_connection(connection,
+						    message, message_len,
+						    response);
 
 	ipc_client_close_connection(connection);
 
@@ -458,7 +487,7 @@ static int do_io(struct ipc_server_thread_data *server_thread_data)
 	if (ret >= 0) {
 		ret = server_thread_data->server_data->application_cb(
 			server_thread_data->server_data->application_data,
-			buf.buf, do_io_reply_callback, &reply_data);
+			buf.buf, buf.len, do_io_reply_callback, &reply_data);
 
 		packet_flush_gently(reply_data.fd);
 
@@ -565,11 +594,132 @@ finished:
 	return NULL;
 }
 
+/*
+ * We need to build a Windows "SECURITY_ATTRIBUTES" object and use it
+ * to apply an ACL when we create the initial instance of the Named
+ * Pipe.  The construction is somewhat involved and consists of
+ * several sequential steps and intermediate objects.
+ *
+ * We use this structure to hold these intermediate pointers so that
+ * we can free them as a group.  (It is unclear from the docs whether
+ * some of these intermediate pointers can be freed before we are
+ * finished using the "lpSA" member.)
+ */
+struct my_sa_data
+{
+	PSID pEveryoneSID;
+	PACL pACL;
+	PSECURITY_DESCRIPTOR pSD;
+	LPSECURITY_ATTRIBUTES lpSA;
+};
+
+static void init_sa(struct my_sa_data *d)
+{
+	memset(d, 0, sizeof(*d));
+}
+
+static void release_sa(struct my_sa_data *d)
+{
+	if (d->pEveryoneSID)
+		FreeSid(d->pEveryoneSID);
+	if (d->pACL)
+		LocalFree(d->pACL);
+	if (d->pSD)
+		LocalFree(d->pSD);
+	if (d->lpSA)
+		LocalFree(d->lpSA);
+
+	memset(d, 0, sizeof(*d));
+}
+
+/*
+ * Create SECURITY_ATTRIBUTES to apply to the initial named pipe.  The
+ * creator of the first server instance gets to set the ACLs on it.
+ *
+ * We allow the well-known group `EVERYONE` to have read+write access
+ * to the named pipe so that clients can send queries to the daemon
+ * and receive the response.
+ *
+ * Normally, this is not necessary since the daemon is usually
+ * automatically started by a foreground command like `git status`,
+ * but in those cases where an elevated Git command started the daemon
+ * (such that the daemon itself runs with elevation), we need to add
+ * the ACL so that non-elevated commands can write to it.
+ *
+ * The following document was helpful:
+ * https://docs.microsoft.com/en-us/windows/win32/secauthz/creating-a-security-descriptor-for-a-new-object-in-c--
+ *
+ * Returns d->lpSA set to a SA or NULL.
+ */
+static LPSECURITY_ATTRIBUTES get_sa(struct my_sa_data *d)
+{
+	SID_IDENTIFIER_AUTHORITY sid_auth_world = SECURITY_WORLD_SID_AUTHORITY;
+#define NR_EA (1)
+	EXPLICIT_ACCESS ea[NR_EA];
+	DWORD dwResult;
+
+	if (!AllocateAndInitializeSid(&sid_auth_world, 1,
+				      SECURITY_WORLD_RID, 0,0,0,0,0,0,0,
+				      &d->pEveryoneSID)) {
+		DWORD gle = GetLastError();
+		trace2_data_intmax("ipc-debug", NULL, "alloc-world-sid/gle",
+				   (intmax_t)gle);
+		goto fail;
+	}
+
+	memset(ea, 0, NR_EA * sizeof(EXPLICIT_ACCESS));
+
+	ea[0].grfAccessPermissions = GENERIC_READ | GENERIC_WRITE;
+	ea[0].grfAccessMode = SET_ACCESS;
+	ea[0].grfInheritance = NO_INHERITANCE;
+	ea[0].Trustee.MultipleTrusteeOperation = NO_MULTIPLE_TRUSTEE;
+	ea[0].Trustee.TrusteeForm = TRUSTEE_IS_SID;
+	ea[0].Trustee.TrusteeType = TRUSTEE_IS_WELL_KNOWN_GROUP;
+	ea[0].Trustee.ptstrName = (LPTSTR)d->pEveryoneSID;
+
+	dwResult = SetEntriesInAcl(NR_EA, ea, NULL, &d->pACL);
+	if (dwResult != ERROR_SUCCESS) {
+		DWORD gle = GetLastError();
+		trace2_data_intmax("ipc-debug", NULL, "set-acl-entry/gle",
+				   (intmax_t)gle);
+		trace2_data_intmax("ipc-debug", NULL, "set-acl-entry/dw",
+				   (intmax_t)dwResult);
+		goto fail;
+	}
+
+	d->pSD = (PSECURITY_DESCRIPTOR)LocalAlloc(
+		LPTR, SECURITY_DESCRIPTOR_MIN_LENGTH);
+	if (!InitializeSecurityDescriptor(d->pSD, SECURITY_DESCRIPTOR_REVISION)) {
+		DWORD gle = GetLastError();
+		trace2_data_intmax("ipc-debug", NULL, "init-sd/gle", (intmax_t)gle);
+		goto fail;
+	}
+
+	if (!SetSecurityDescriptorDacl(d->pSD, TRUE, d->pACL, FALSE)) {
+		DWORD gle = GetLastError();
+		trace2_data_intmax("ipc-debug", NULL, "set-sd-dacl/gle", (intmax_t)gle);
+		goto fail;
+	}
+
+	d->lpSA = (LPSECURITY_ATTRIBUTES)LocalAlloc(LPTR, sizeof(SECURITY_ATTRIBUTES));
+	d->lpSA->nLength = sizeof(SECURITY_ATTRIBUTES);
+	d->lpSA->lpSecurityDescriptor = d->pSD;
+	d->lpSA->bInheritHandle = FALSE;
+
+	return d->lpSA;
+
+fail:
+	release_sa(d);
+	return NULL;
+}
+
 static HANDLE create_new_pipe(wchar_t *wpath, int is_first)
 {
 	HANDLE hPipe;
 	DWORD dwOpenMode, dwPipeMode;
-	LPSECURITY_ATTRIBUTES lpsa = NULL;
+	struct my_sa_data my_sa_data;
+
+	init_sa(&my_sa_data);
 
 	dwOpenMode = PIPE_ACCESS_INBOUND | PIPE_ACCESS_OUTBOUND |
 		FILE_FLAG_OVERLAPPED;
@@ -585,20 +735,15 @@ static HANDLE create_new_pipe(wchar_t *wpath, int is_first)
 		 * set the ACL / Security Attributes on the named
 		 * pipe; subsequent instances inherit and cannot
 		 * change them.
-		 *
-		 * TODO Should we allow the application layer to
-		 * specify security attributes, such as `LocalService`
-		 * or `LocalSystem`, when we create the named pipe?
-		 * This question is probably not important when the
-		 * daemon is started by a foreground user process and
-		 * only needs to talk to the current user, but may be
-		 * if the daemon is run via the Control Panel as a
-		 * System Service.
 		 */
+		get_sa(&my_sa_data);
 	}
 
 	hPipe = CreateNamedPipeW(wpath, dwOpenMode, dwPipeMode,
-				 PIPE_UNLIMITED_INSTANCES, 1024, 1024, 0, lpsa);
+				 PIPE_UNLIMITED_INSTANCES, 1024, 1024, 0,
+				 my_sa_data.lpSA);
+
+	release_sa(&my_sa_data);
 
 	return hPipe;
 }

run-command.c

@@ -1874,3 +1874,132 @@ void prepare_other_repo_env(struct strvec *env_array, const char *new_git_dir)
 	}
 	strvec_pushf(env_array, "%s=%s", GIT_DIR_ENVIRONMENT, new_git_dir);
 }
+
+enum start_bg_result start_bg_command(struct child_process *cmd,
+				      start_bg_wait_cb *wait_cb,
+				      void *cb_data,
+				      unsigned int timeout_sec)
+{
+	enum start_bg_result sbgr = SBGR_ERROR;
+	int ret;
+	int wait_status;
+	pid_t pid_seen;
+	time_t time_limit;
+
+	/*
+	 * We do not allow clean-on-exit because the child process
+	 * should persist in the background and possibly/probably
+	 * after this process exits.  So we don't want to kill the
+	 * child during our atexit routine.
+	 */
+	if (cmd->clean_on_exit)
+		BUG("start_bg_command() does not allow non-zero clean_on_exit");
+
+	if (!cmd->trace2_child_class)
+		cmd->trace2_child_class = "background";
+
+	ret = start_command(cmd);
+	if (ret) {
+		/*
+		 * We assume that if `start_command()` fails, we
+		 * either get a complete `trace2_child_start() /
+		 * trace2_child_exit()` pair or it fails before the
+		 * `trace2_child_start()` is emitted, so we do not
+		 * need to worry about it here.
+		 *
+		 * We also assume that `start_command()` does not add
+		 * us to the cleanup list.  And that it calls
+		 * calls `child_process_clear()`.
+		 */
+		sbgr = SBGR_ERROR;
+		goto done;
+	}
+
+	time(&time_limit);
+	time_limit += timeout_sec;
+
+wait:
+	pid_seen = waitpid(cmd->pid, &wait_status, WNOHANG);
+
+	if (!pid_seen) {
+		/*
+		 * The child is currently running.  Ask the callback
+		 * if the child is ready to do work or whether we
+		 * should keep waiting for it to boot up.
+		 */
+		ret = (*wait_cb)(cmd, cb_data);
+		if (!ret) {
+			/*
+			 * The child is running and "ready".
+			 */
+			trace2_child_ready(cmd, "ready");
+			sbgr = SBGR_READY;
+			goto done;
+		} else if (ret > 0) {
+			/*
+			 * The callback said to give it more time to boot up
+			 * (subject to our timeout limit).
+			 */
+			time_t now;
+
+			time(&now);
+			if (now < time_limit)
+				goto wait;
+
+			/*
+			 * Our timeout has expired.  We don't try to
+			 * kill the child, but rather let it continue
+			 * (hopefully) trying to startup.
+			 */
+			trace2_child_ready(cmd, "timeout");
+			sbgr = SBGR_TIMEOUT;
+			goto done;
+		} else {
+			/*
+			 * The cb gave up on this child.  It is still running,
+			 * but our cb got an error trying to probe it.
+			 */
+			trace2_child_ready(cmd, "error");
+			sbgr = SBGR_CB_ERROR;
+			goto done;
+		}
+	}
+
+	else if (pid_seen == cmd->pid) {
+		int child_code = -1;
+
+		/*
+		 * The child started, but exited or was terminated
+		 * before becoming "ready".
+		 *
+		 * We try to match the behavior of `wait_or_whine()`
+		 * WRT the handling of WIFSIGNALED() and WIFEXITED()
+		 * and convert the child's status to a return code for
+		 * tracing purposes and emit the `trace2_child_exit()`
+		 * event.
+		 *
+		 * We do not want the wait_or_whine() error message
+		 * because we will be called by client-side library
+		 * routines.
+		 */
+		if (WIFEXITED(wait_status))
+			child_code = WEXITSTATUS(wait_status);
+		else if (WIFSIGNALED(wait_status))
+			child_code = WTERMSIG(wait_status) + 128;
+		trace2_child_exit(cmd, child_code);
+
+		sbgr = SBGR_DIED;
+		goto done;
+	}
+
+	else if (pid_seen < 0 && errno == EINTR)
+		goto wait;
+
+	trace2_child_exit(cmd, -1);
+	sbgr = SBGR_ERROR;
+
+done:
+	child_process_clear(cmd);
+	invalidate_lstat_cache();
+	return sbgr;
+}

run-command.h

@@ -510,4 +510,61 @@ int run_processes_parallel_tr2(int n, get_next_task_fn, start_failure_fn,
  */
 void prepare_other_repo_env(struct strvec *env_array, const char *new_git_dir);
 
+/**
+ * Possible return values for start_bg_command().
+ */
+enum start_bg_result {
+	/* child process is "ready" */
+	SBGR_READY = 0,
+
+	/* child process could not be started */
+	SBGR_ERROR,
+
+	/* callback error when testing for "ready" */
+	SBGR_CB_ERROR,
+
+	/* timeout expired waiting for child to become "ready" */
+	SBGR_TIMEOUT,
+
+	/* child process exited or was signalled before becomming "ready" */
+	SBGR_DIED,
+};
+
+/**
+ * Callback used by start_bg_command() to ask whether the
+ * child process is ready or needs more time to become "ready".
+ *
+ * The callback will receive the cmd and cb_data arguments given to
+ * start_bg_command().
+ *
+ * Returns 1 is child needs more time (subject to the requested timeout).
+ * Returns 0 if child is "ready".
+ * Returns -1 on any error and cause start_bg_command() to also error out.
+ */
+typedef int(start_bg_wait_cb)(const struct child_process *cmd, void *cb_data);
+
+/**
+ * Start a command in the background.  Wait long enough for the child
+ * to become "ready" (as defined by the provided callback).  Capture
+ * immediate errors (like failure to start) and any immediate exit
+ * status (such as a shutdown/signal before the child became "ready")
+ * and return this like start_command().
+ *
+ * We run a custom wait loop using the provided callback to wait for
+ * the child to start and become "ready".  This is limited by the given
+ * timeout value.
+ *
+ * If the child does successfully start and become "ready", we orphan
+ * it into the background.
+ *
+ * The caller must not call finish_command().
+ *
+ * The opaque cb_data argument will be forwarded to the callback for
+ * any instance data that it might require.  This may be NULL.
+ */
+enum start_bg_result start_bg_command(struct child_process *cmd,
+				      start_bg_wait_cb *wait_cb,
+				      void *cb_data,
+				      unsigned int timeout_sec);
+
 #endif

simple-ipc.h

@@ -5,13 +5,6 @@
  * See Documentation/technical/api-simple-ipc.txt
  */
 
-#ifdef SUPPORTS_SIMPLE_IPC
-#include "pkt-line.h"
-
-/*
- * Simple IPC Client Side API.
- */
-
 enum ipc_active_state {
 	/*
 	 * The pipe/socket exists and the daemon is waiting for connections.
@@ -43,6 +36,13 @@ enum ipc_active_state {
 	IPC_STATE__OTHER_ERROR,
 };
 
+#ifdef SUPPORTS_SIMPLE_IPC
+#include "pkt-line.h"
+
+/*
+ * Simple IPC Client Side API.
+ */
+
 struct ipc_client_connect_options {
 	/*
 	 * Spin under timeout if the server is running but can't
@@ -103,7 +103,8 @@ void ipc_client_close_connection(struct ipc_client_connection *connection);
  */
 int ipc_client_send_command_to_connection(
 	struct ipc_client_connection *connection,
-	const char *message, struct strbuf *answer);
+	const char *message, size_t message_len,
+	struct strbuf *answer);
 
 /*
  * Used by the client to synchronously connect and send and receive a
@@ -115,7 +116,8 @@ int ipc_client_send_command_to_connection(
  */
 int ipc_client_send_command(const char *path,
 			    const struct ipc_client_connect_options *options,
-			    const char *message, struct strbuf *answer);
+			    const char *message, size_t message_len,
+			    struct strbuf *answer);
 
 /*
  * Simple IPC Server Side API.
@@ -140,6 +142,7 @@ typedef int (ipc_server_reply_cb)(struct ipc_server_reply_data *,
  */
 typedef int (ipc_server_application_cb)(void *application_data,
 					const char *request,
+					size_t request_len,
 					ipc_server_reply_cb *reply_cb,
 					struct ipc_server_reply_data *reply_data);
 

t/helper/test-simple-ipc.c

@@ -9,6 +9,7 @@
 #include "parse-options.h"
 #include "thread-utils.h"
 #include "strvec.h"
+#include "run-command.h"
 
 #ifndef SUPPORTS_SIMPLE_IPC
 int cmd__simple_ipc(int argc, const char **argv)
@@ -112,7 +113,7 @@ static int app__slow_command(ipc_server_reply_cb *reply_cb,
 /*
  * The client sent a command followed by a (possibly very) large buffer.
  */
-static int app__sendbytes_command(const char *received,
+static int app__sendbytes_command(const char *received, size_t received_len,
 				  ipc_server_reply_cb *reply_cb,
 				  struct ipc_server_reply_data *reply_data)
 {
@@ -123,6 +124,13 @@ static int app__sendbytes_command(const char *received,
 	int errs = 0;
 	int ret;
 
+	/*
+	 * The test is setup to send:
+	 *     "sendbytes" SP <n * char>
+	 */
+	if (received_len < strlen("sendbytes "))
+		BUG("received_len is short in app__sendbytes_command");
+
 	if (skip_prefix(received, "sendbytes ", &p))
 		len_ballast = strlen(p);
 
@@ -160,7 +168,7 @@ static ipc_server_application_cb test_app_cb;
  * by this application.
  */
 static int test_app_cb(void *application_data,
-		       const char *command,
+		       const char *command, size_t command_len,
 		       ipc_server_reply_cb *reply_cb,
 		       struct ipc_server_reply_data *reply_data)
 {
@@ -173,7 +181,7 @@ static int test_app_cb(void *application_data,
 	if (application_data != (void*)&my_app_data)
 		BUG("application_cb: application_data pointer wrong");
 
-	if (!strcmp(command, "quit")) {
+	if (command_len == 4 && !strncmp(command, "quit", 4)) {
 		/*
 		 * The client sent a "quit" command.  This is an async
 		 * request for the server to shutdown.
@@ -193,22 +201,23 @@ static int test_app_cb(void *application_data,
 		return SIMPLE_IPC_QUIT;
 	}
 
-	if (!strcmp(command, "ping")) {
+	if (command_len == 4 && !strncmp(command, "ping", 4)) {
 		const char *answer = "pong";
 		return reply_cb(reply_data, answer, strlen(answer));
 	}
 
-	if (!strcmp(command, "big"))
+	if (command_len == 3 && !strncmp(command, "big", 3))
 		return app__big_command(reply_cb, reply_data);
 
-	if (!strcmp(command, "chunk"))
+	if (command_len == 5 && !strncmp(command, "chunk", 5))
 		return app__chunk_command(reply_cb, reply_data);
 
-	if (!strcmp(command, "slow"))
+	if (command_len == 4 && !strncmp(command, "slow", 4))
 		return app__slow_command(reply_cb, reply_data);
 
-	if (starts_with(command, "sendbytes "))
-		return app__sendbytes_command(command, reply_cb, reply_data);
+	if (command_len >= 10 && starts_with(command, "sendbytes "))
+		return app__sendbytes_command(command, command_len,
+					      reply_cb, reply_data);
 
 	return app__unhandled_command(command, reply_cb, reply_data);
 }
@@ -259,185 +268,71 @@ static int daemon__run_server(void)
 	 */
 	ret = ipc_server_run(cl_args.path, &opts, test_app_cb, (void*)&my_app_data);
 	if (ret == -2)
-		error(_("socket/pipe already in use: '%s'"), cl_args.path);
+		error("socket/pipe already in use: '%s'", cl_args.path);
 	else if (ret == -1)
-		error_errno(_("could not start server on: '%s'"), cl_args.path);
+		error_errno("could not start server on: '%s'", cl_args.path);
 
 	return ret;
 }
 
-#ifndef GIT_WINDOWS_NATIVE
-/*
- * This is adapted from `daemonize()`.  Use `fork()` to directly create and
- * run the daemon in a child process.
- */
-static int spawn_server(pid_t *pid)
-{
-	struct ipc_server_opts opts = {
-		.nr_threads = cl_args.nr_threads,
-	};
-
-	*pid = fork();
+static start_bg_wait_cb bg_wait_cb;
 
-	switch (*pid) {
-	case 0:
-		if (setsid() == -1)
-			error_errno(_("setsid failed"));
-		close(0);
-		close(1);
-		close(2);
-		sanitize_stdfds();
+static int bg_wait_cb(const struct child_process *cp, void *cb_data)
+{
+	int s = ipc_get_active_state(cl_args.path);
 
-		return ipc_server_run(cl_args.path, &opts, test_app_cb,
-				      (void*)&my_app_data);
+	switch (s) {
+	case IPC_STATE__LISTENING:
+		/* child is "ready" */
+		return 0;
 
-	case -1:
-		return error_errno(_("could not spawn daemon in the background"));
+	case IPC_STATE__NOT_LISTENING:
+	case IPC_STATE__PATH_NOT_FOUND:
+		/* give child more time */
+		return 1;
 
 	default:
-		return 0;
+	case IPC_STATE__INVALID_PATH:
+	case IPC_STATE__OTHER_ERROR:
+		/* all the time in world won't help */
+		return -1;
 	}
 }
-#else
-/*
- * Conceptually like `daemonize()` but different because Windows does not
- * have `fork(2)`.  Spawn a normal Windows child process but without the
- * limitations of `start_command()` and `finish_command()`.
- */
-static int spawn_server(pid_t *pid)
-{
-	char test_tool_exe[MAX_PATH];
-	struct strvec args = STRVEC_INIT;
-	int in, out;
-
-	GetModuleFileNameA(NULL, test_tool_exe, MAX_PATH);
-
-	in = open("/dev/null", O_RDONLY);
-	out = open("/dev/null", O_WRONLY);
-
-	strvec_push(&args, test_tool_exe);
-	strvec_push(&args, "simple-ipc");
-	strvec_push(&args, "run-daemon");
-	strvec_pushf(&args, "--name=%s", cl_args.path);
-	strvec_pushf(&args, "--threads=%d", cl_args.nr_threads);
 
-	*pid = mingw_spawnvpe(args.v[0], args.v, NULL, NULL, in, out, out);
-	close(in);
-	close(out);
-
-	strvec_clear(&args);
-
-	if (*pid < 0)
-		return error(_("could not spawn daemon in the background"));
-
-	return 0;
-}
-#endif
-
-/*
- * This is adapted from `wait_or_whine()`.  Watch the child process and
- * let it get started and begin listening for requests on the socket
- * before reporting our success.
- */
-static int wait_for_server_startup(pid_t pid_child)
+static int daemon__start_server(void)
 {
-	int status;
-	pid_t pid_seen;
-	enum ipc_active_state s;
-	time_t time_limit, now;
+	struct child_process cp = CHILD_PROCESS_INIT;
+	enum start_bg_result sbgr;
 
-	time(&time_limit);
-	time_limit += cl_args.max_wait_sec;
+	strvec_push(&cp.args, "test-tool");
+	strvec_push(&cp.args, "simple-ipc");
+	strvec_push(&cp.args, "run-daemon");
+	strvec_pushf(&cp.args, "--name=%s", cl_args.path);
+	strvec_pushf(&cp.args, "--threads=%d", cl_args.nr_threads);
 
-	for (;;) {
-		pid_seen = waitpid(pid_child, &status, WNOHANG);
-
-		if (pid_seen == -1)
-			return error_errno(_("waitpid failed"));
-
-		else if (pid_seen == 0) {
-			/*
-			 * The child is still running (this should be
-			 * the normal case).  Try to connect to it on
-			 * the socket and see if it is ready for
-			 * business.
-			 *
-			 * If there is another daemon already running,
-			 * our child will fail to start (possibly
-			 * after a timeout on the lock), but we don't
-			 * care (who responds) if the socket is live.
-			 */
-			s = ipc_get_active_state(cl_args.path);
-			if (s == IPC_STATE__LISTENING)
-				return 0;
+	cp.no_stdin = 1;
+	cp.no_stdout = 1;
+	cp.no_stderr = 1;
 
-			time(&now);
-			if (now > time_limit)
-				return error(_("daemon not online yet"));
+	sbgr = start_bg_command(&cp, bg_wait_cb, NULL, cl_args.max_wait_sec);
 
-			continue;
-		}
+	switch (sbgr) {
+	case SBGR_READY:
+		return 0;
 
-		else if (pid_seen == pid_child) {
-			/*
-			 * The new child daemon process shutdown while
-			 * it was starting up, so it is not listening
-			 * on the socket.
-			 *
-			 * Try to ping the socket in the odd chance
-			 * that another daemon started (or was already
-			 * running) while our child was starting.
-			 *
-			 * Again, we don't care who services the socket.
-			 */
-			s = ipc_get_active_state(cl_args.path);
-			if (s == IPC_STATE__LISTENING)
-				return 0;
+	default:
+	case SBGR_ERROR:
+	case SBGR_CB_ERROR:
+		return error("daemon failed to start");
 
-			/*
-			 * We don't care about the WEXITSTATUS() nor
-			 * any of the WIF*(status) values because
-			 * `cmd__simple_ipc()` does the `!!result`
-			 * trick on all function return values.
-			 *
-			 * So it is sufficient to just report the
-			 * early shutdown as an error.
-			 */
-			return error(_("daemon failed to start"));
-		}
+	case SBGR_TIMEOUT:
+		return error("daemon not online yet");
 
-		else
-			return error(_("waitpid is confused"));
+	case SBGR_DIED:
+		return error("daemon terminated");
 	}
 }
 
-/*
- * This process will start a simple-ipc server in a background process and
- * wait for it to become ready.  This is like `daemonize()` but gives us
- * more control and better error reporting (and makes it easier to write
- * unit tests).
- */
-static int daemon__start_server(void)
-{
-	pid_t pid_child;
-	int ret;
-
-	/*
-	 * Run the actual daemon in a background process.
-	 */
-	ret = spawn_server(&pid_child);
-	if (pid_child <= 0)
-		return ret;
-
-	/*
-	 * Let the parent wait for the child process to get started
-	 * and begin listening for requests on the socket.
-	 */
-	ret = wait_for_server_startup(pid_child);
-
-	return ret;
-}
-
 /*
  * This process will run a quick probe to see if a simple-ipc server
  * is active on this path.
@@ -488,7 +383,9 @@ static int client__send_ipc(void)
 	options.wait_if_busy = 1;
 	options.wait_if_not_found = 0;
 
-	if (!ipc_client_send_command(cl_args.path, &options, command, &buf)) {
+	if (!ipc_client_send_command(cl_args.path, &options,
+				     command, strlen(command),
+				     &buf)) {
 		if (buf.len) {
 			printf("%s\n", buf.buf);
 			fflush(stdout);
@@ -538,7 +435,7 @@ static int client__stop_server(void)
 
 		time(&now);
 		if (now > time_limit)
-			return error(_("daemon has not shutdown yet"));
+			return error("daemon has not shutdown yet");
 	}
 }
 
@@ -556,7 +453,9 @@ static int do_sendbytes(int bytecount, char byte, const char *path,
 	strbuf_addstr(&buf_send, "sendbytes ");
 	strbuf_addchars(&buf_send, byte, bytecount);
 
-	if (!ipc_client_send_command(path, options, buf_send.buf, &buf_resp)) {
+	if (!ipc_client_send_command(path, options,
+				     buf_send.buf, buf_send.len,
+				     &buf_resp)) {
 		strbuf_rtrim(&buf_resp);
 		printf("sent:%c%08d %s\n", byte, bytecount, buf_resp.buf);
 		fflush(stdout);

trace2.c

@@ -394,6 +394,37 @@ void trace2_child_exit_fl(const char *file, int line, struct child_process *cmd,
 						 us_elapsed_child);
 }
 
+void trace2_child_ready_fl(const char *file, int line,
+			   struct child_process *cmd,
+			   const char *ready)
+{
+	struct tr2_tgt *tgt_j;
+	int j;
+	uint64_t us_now;
+	uint64_t us_elapsed_absolute;
+	uint64_t us_elapsed_child;
+
+	if (!trace2_enabled)
+		return;
+
+	us_now = getnanotime() / 1000;
+	us_elapsed_absolute = tr2tls_absolute_elapsed(us_now);
+
+	if (cmd->trace2_child_us_start)
+		us_elapsed_child = us_now - cmd->trace2_child_us_start;
+	else
+		us_elapsed_child = 0;
+
+	for_each_wanted_builtin (j, tgt_j)
+		if (tgt_j->pfn_child_ready_fl)
+			tgt_j->pfn_child_ready_fl(file, line,
+						  us_elapsed_absolute,
+						  cmd->trace2_child_id,
+						  cmd->pid,
+						  ready,
+						  us_elapsed_child);
+}
+
 int trace2_exec_fl(const char *file, int line, const char *exe,
 		   const char **argv)
 {

trace2.h

@@ -253,6 +253,31 @@ void trace2_child_exit_fl(const char *file, int line, struct child_process *cmd,
 #define trace2_child_exit(cmd, code) \
 	trace2_child_exit_fl(__FILE__, __LINE__, (cmd), (code))
 
+/**
+ * Emits a "child_ready" message containing the "child-id" and a flag
+ * indicating whether the child was considered "ready" when we
+ * released it.
+ *
+ * This function should be called after starting a daemon process in
+ * the background (and after giving it sufficient time to boot
+ * up) to indicate that we no longer control or own it.
+ *
+ * The "ready" argument should contain one of { "ready", "timeout",
+ * "error" } to indicate the state of the running daemon when we
+ * released it.
+ *
+ * If the daemon process fails to start or it exits or is terminated
+ * while we are still waiting for it, the caller should emit a
+ * regular "child_exit" to report the normal process exit information.
+ *
+ */
+void trace2_child_ready_fl(const char *file, int line,
+			   struct child_process *cmd,
+			   const char *ready);
+
+#define trace2_child_ready(cmd, ready) \
+	trace2_child_ready_fl(__FILE__, __LINE__, (cmd), (ready))
+
 /**
  * Emit an 'exec' event prior to calling one of exec(), execv(),
  * execvp(), and etc.  On Unix-derived systems, this will be the

trace2/tr2_tgt.h

@@ -45,6 +45,10 @@ typedef void(tr2_tgt_evt_child_exit_fl_t)(const char *file, int line,
 					  uint64_t us_elapsed_absolute, int cid,
 					  int pid, int code,
 					  uint64_t us_elapsed_child);
+typedef void(tr2_tgt_evt_child_ready_fl_t)(const char *file, int line,
+					   uint64_t us_elapsed_absolute,
+					   int cid, int pid, const char *ready,
+					   uint64_t us_elapsed_child);
 
 typedef void(tr2_tgt_evt_thread_start_fl_t)(const char *file, int line,
 					    uint64_t us_elapsed_absolute);
@@ -116,6 +120,7 @@ struct tr2_tgt {
 	tr2_tgt_evt_alias_fl_t                  *pfn_alias_fl;
 	tr2_tgt_evt_child_start_fl_t            *pfn_child_start_fl;
 	tr2_tgt_evt_child_exit_fl_t             *pfn_child_exit_fl;
+	tr2_tgt_evt_child_ready_fl_t            *pfn_child_ready_fl;
 	tr2_tgt_evt_thread_start_fl_t           *pfn_thread_start_fl;
 	tr2_tgt_evt_thread_exit_fl_t            *pfn_thread_exit_fl;
 	tr2_tgt_evt_exec_fl_t                   *pfn_exec_fl;

trace2/tr2_tgt_event.c

@@ -383,6 +383,27 @@ static void fn_child_exit_fl(const char *file, int line,
 	jw_release(&jw);
 }
 
+static void fn_child_ready_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute, int cid, int pid,
+			      const char *ready, uint64_t us_elapsed_child)
+{
+	const char *event_name = "child_ready";
+	struct json_writer jw = JSON_WRITER_INIT;
+	double t_rel = (double)us_elapsed_child / 1000000.0;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, file, line, NULL, &jw);
+	jw_object_intmax(&jw, "child_id", cid);
+	jw_object_intmax(&jw, "pid", pid);
+	jw_object_string(&jw, "ready", ready);
+	jw_object_double(&jw, "t_rel", 6, t_rel);
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+
+	jw_release(&jw);
+}
+
 static void fn_thread_start_fl(const char *file, int line,
 			       uint64_t us_elapsed_absolute)
 {
@@ -610,6 +631,7 @@ struct tr2_tgt tr2_tgt_event = {
 	fn_alias_fl,
 	fn_child_start_fl,
 	fn_child_exit_fl,
+	fn_child_ready_fl,
 	fn_thread_start_fl,
 	fn_thread_exit_fl,
 	fn_exec_fl,

trace2/tr2_tgt_normal.c

@@ -251,6 +251,19 @@ static void fn_child_exit_fl(const char *file, int line,
 	strbuf_release(&buf_payload);
 }
 
+static void fn_child_ready_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute, int cid, int pid,
+			      const char *ready, uint64_t us_elapsed_child)
+{
+	struct strbuf buf_payload = STRBUF_INIT;
+	double elapsed = (double)us_elapsed_child / 1000000.0;
+
+	strbuf_addf(&buf_payload, "child_ready[%d] pid:%d ready:%s elapsed:%.6f",
+		    cid, pid, ready, elapsed);
+	normal_io_write_fl(file, line, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
 static void fn_exec_fl(const char *file, int line, uint64_t us_elapsed_absolute,
 		       int exec_id, const char *exe, const char **argv)
 {
@@ -330,6 +343,7 @@ struct tr2_tgt tr2_tgt_normal = {
 	fn_alias_fl,
 	fn_child_start_fl,
 	fn_child_exit_fl,
+	fn_child_ready_fl,
 	NULL, /* thread_start */
 	NULL, /* thread_exit */
 	fn_exec_fl,

trace2/tr2_tgt_perf.c

@@ -360,6 +360,20 @@ static void fn_child_exit_fl(const char *file, int line,
 	strbuf_release(&buf_payload);
 }
 
+static void fn_child_ready_fl(const char *file, int line,
+			      uint64_t us_elapsed_absolute, int cid, int pid,
+			      const char *ready, uint64_t us_elapsed_child)
+{
+	const char *event_name = "child_ready";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, "[ch%d] pid:%d ready:%s", cid, pid, ready);
+
+	perf_io_write_fl(file, line, event_name, NULL, &us_elapsed_absolute,
+			 &us_elapsed_child, NULL, &buf_payload);
+	strbuf_release(&buf_payload);
+}
+
 static void fn_thread_start_fl(const char *file, int line,
 			       uint64_t us_elapsed_absolute)
 {
@@ -553,6 +567,7 @@ struct tr2_tgt tr2_tgt_perf = {
 	fn_alias_fl,
 	fn_child_start_fl,
 	fn_child_exit_fl,
+	fn_child_ready_fl,
 	fn_thread_start_fl,
 	fn_thread_exit_fl,
 	fn_exec_fl,