Fix hang after end of backup

The buggy behavior was that the 'adb backup ....' host command line
invocation would hang forever, even after the backup finished and
the forked device-side subprocess had been reaped.  The reason for
this is that the device adbd end of the socketpair used to send
the data back from the forked subprocess was still stuck readable
even after the remote end of it had been closed.

With this patch, the thread whose job it is to waitpid() in order
to harvest the forked child process also closes the local (adbd)
end of the socketpair.  This makes the fdevent logic notice that
the socket is dead, at which point it cleans up everything including
the communication back to the host.

Change-Id: I90e7e4e5db36c5a6f7363708b29a6d2c56d1250e

1 files changed, 17 insertions, 4 deletions

diff --git a/adb/backup_service.c b/adb/backup_service.c
index 4f0c8ac..669ff86 100644
--- a/adb/backup_service.c
+++ b/adb/backup_service.c
@@ -22,6 +22,11 @@
 #define TRACE_TAG  TRACE_ADB
 #include "adb.h"
 
+typedef struct {
+    pid_t pid;
+    int fd;
+} backup_harvest_params;
+
 // socketpair but do *not* mark as close_on_exec
 static int backup_socketpair(int sv[2]) {
     int rc = unix_socketpair( AF_UNIX, SOCK_STREAM, 0, sv );
@@ -31,11 +36,14 @@ static int backup_socketpair(int sv[2]) {
     return 0;
 }
 
-static void* backup_child_waiter(void* pid_cookie) {
+// harvest the child process then close the read end of the socketpair
+static void* backup_child_waiter(void* args) {
     int status;
+    backup_harvest_params* params = (backup_harvest_params*) args;
 
-    waitpid((pid_t) pid_cookie, &status, 0);
-    D("harvested backup/restore child, status=%d\n", status);
+    waitpid(params->pid, &status, 0);
+    adb_close(params->fd);
+    free(params);
     return NULL;
 }
 
@@ -124,14 +132,19 @@ int backup_service(BackupOperation op, char* args) {
         exit(-1);
     } else {
         adb_thread_t t;
+        backup_harvest_params* params;
 
         // parent, i.e. adbd -- close the sending half of the socket
         D("fork() returned pid %d\n", pid);
         adb_close(s[1]);
 
         // spin a thread to harvest the child process
-        if (adb_thread_create(&t, backup_child_waiter, (void*)pid)) {
+        params = (backup_harvest_params*) malloc(sizeof(backup_harvest_params));
+        params->pid = pid;
+        params->fd = s[0];
+        if (adb_thread_create(&t, backup_child_waiter, params)) {
             adb_close(s[0]);
+            free(params);
             D("Unable to create child harvester\n");
             return -1;
         }