From 2295de2c97e6d1290a86e0b160885212411510a5 Mon Sep 17 00:00:00 2001
From: David Kalnischkies <david@kalnischkies.de>
Date: Sun, 9 Sep 2018 19:45:42 +0200
Subject: Process status-fd completely before finishing dpkg call

Exiting the processing loop as soon as the dpkg process finishes might
leave status-fd lines unprocessed which wasn't much of a problem in the
past as the progress would just be slightly off, but now that we us the
information also for skipping already done tasks and generate warnings
if we didn't see all expected messages we should make sure we seem them
all. We still need to exit "early" if dpkg exited unsuccessfully/crashed
through as the (remaining) status lines we get could be incomplete.
---
 apt-pkg/deb/dpkgpm.cc | 51 ++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 36 insertions(+), 15 deletions(-)

diff --git a/apt-pkg/deb/dpkgpm.cc b/apt-pkg/deb/dpkgpm.cc
index 790019b98..68674fa02 100644
--- a/apt-pkg/deb/dpkgpm.cc
+++ b/apt-pkg/deb/dpkgpm.cc
@@ -102,8 +102,8 @@ APT_PURE static unsigned int EnvironmentSize()				/*{{{*/
 class pkgDPkgPMPrivate							/*{{{*/
 {
 public:
-   pkgDPkgPMPrivate() : stdin_is_dev_null(false), dpkgbuf_pos(0),
-			term_out(NULL), history_out(NULL),
+   pkgDPkgPMPrivate() : stdin_is_dev_null(false), status_fd_reached_end_of_file(false),
+			dpkgbuf_pos(0), term_out(NULL), history_out(NULL),
 			progress(NULL), tt_is_valid(false), master(-1),
 			slave(NULL), protect_slave_from_dying(-1),
 			direct_stdin(false)
@@ -114,6 +114,7 @@ public:
    {
    }
    bool stdin_is_dev_null;
+   bool status_fd_reached_end_of_file;
    // the buffer we use for the dpkg status-fd reading
    char dpkgbuf[1024];
    size_t dpkgbuf_pos;
@@ -958,11 +959,19 @@ void pkgDPkgPM::handleCrossUpgradeAction(string const &pkgname)		/*{{{*/
 // DPkgPM::DoDpkgStatusFd						/*{{{*/
 void pkgDPkgPM::DoDpkgStatusFd(int statusfd)
 {
-   ssize_t const len = read(statusfd, &d->dpkgbuf[d->dpkgbuf_pos],
-	 (sizeof(d->dpkgbuf)/sizeof(d->dpkgbuf[0])) - d->dpkgbuf_pos);
-   if(len <= 0)
-      return;
-   d->dpkgbuf_pos += (len / sizeof(d->dpkgbuf[0]));
+   auto const remainingBuffer = (sizeof(d->dpkgbuf) / sizeof(d->dpkgbuf[0])) - d->dpkgbuf_pos;
+   if (likely(remainingBuffer > 0) && d->status_fd_reached_end_of_file == false)
+   {
+      auto const len = read(statusfd, &d->dpkgbuf[d->dpkgbuf_pos], remainingBuffer);
+      if (len < 0)
+	 return;
+      else if (len == 0 && d->dpkgbuf_pos == 0)
+      {
+	 d->status_fd_reached_end_of_file = true;
+	 return;
+      }
+      d->dpkgbuf_pos += (len / sizeof(d->dpkgbuf[0]));
+   }
 
    // process line by line from the buffer
    char *p = d->dpkgbuf, *q = nullptr;
@@ -2022,6 +2031,7 @@ bool pkgDPkgPM::Go(APT::Progress::PackageManager *progress)
       // we read from dpkg here
       int const _dpkgin = fd[0];
       close(fd[1]);                        // close the write end of the pipe
+      d->status_fd_reached_end_of_file = false;
 
       // apply ionice
       if (_config->FindB("DPkg::UseIoNice", false) == true)
@@ -2041,14 +2051,24 @@ bool pkgDPkgPM::Go(APT::Progress::PackageManager *progress)
       int Status = 0;
       int res;
       bool waitpid_failure = false;
-      while ((res=waitpid(Child,&Status, WNOHANG)) != Child) {
-	 if(res < 0) {
-	    // error handling, waitpid returned -1
-	    if (errno == EINTR)
-	       continue;
-	    waitpid_failure = true;
-	    break;
+      bool dpkg_finished = false;
+      do
+      {
+	 if (dpkg_finished == false)
+	 {
+	    if ((res = waitpid(Child, &Status, WNOHANG)) == Child)
+	       dpkg_finished = true;
+	    else if (res < 0)
+	    {
+	       // error handling, waitpid returned -1
+	       if (errno == EINTR)
+		  continue;
+	       waitpid_failure = true;
+	       break;
+	    }
 	 }
+	 if (dpkg_finished && d->status_fd_reached_end_of_file)
+	    break;
 
 	 // wait for input or output here
 	 FD_ZERO(&rfds);
@@ -2078,7 +2098,8 @@ bool pkgDPkgPM::Go(APT::Progress::PackageManager *progress)
 	    DoStdin(d->master);
 	 if(FD_ISSET(_dpkgin, &rfds))
 	    DoDpkgStatusFd(_dpkgin);
-      }
+
+      } while (true);
       close(_dpkgin);
 
       // Restore sig int/quit
-- 
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