[6.0] 9ba61d1b0 sess_fail_* detailled accept error counters

[Dridi Boukelmoune]

commit 9ba61d1b02a7d3c98be7c4da369a7392c85aea77
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Mon May 28 16:07:27 2018 +0200

    sess_fail_* detailled accept error counters
    
    We already emitted Debug log records for accept failures, but for
    all practical purposes this is useless for forensics.
    
    These counters will point directly to the root cause for the most
    common issues with sess_fail (accept failures). sess_fail is preserved
    as an overall counter as it will most likely be already monitored for
    many installations.
    
    Ref     #2622
    
    Conflicts:
            doc/changes.rst

diff --git a/bin/varnishd/VSC_main.vsc b/bin/varnishd/VSC_main.vsc
index a2e2d0143..dbcbcdf65 100644
--- a/bin/varnishd/VSC_main.vsc
+++ b/bin/varnishd/VSC_main.vsc
@@ -33,9 +33,46 @@
 .. varnish_vsc:: sess_fail
 	:oneliner:	Session accept failures
 
-	Count of failures to accept TCP connection.  Either the client
-	changed its mind, or the kernel ran out of some resource like file
-	descriptors.
+	Count of failures to accept TCP connection.
+
+	This counter is the sum of the sess_fail_* counters, which
+	give more detailled information.
+
+.. varnish_vsc:: sess_fail_econnaborted
+	:oneliner:	Session accept failures: connection aborted
+
+	Detailled reason for sess_fail: Connection aborted by the
+	client, usually harmless.
+
+.. varnish_vsc:: sess_fail_eintr
+	:oneliner:	Session accept failures: interrupted system call
+
+	Detailled reason for sess_fail: The accept() call was
+	interrupted, usually harmless
+
+.. varnish_vsc:: sess_fail_emfile
+	:oneliner:	Session accept failures: too many open files
+
+	Detailled reason for sess_fail: No file descriptor was
+	available. Consider raising RLIMIT_NOFILE (see ulimit -n).
+
+.. varnish_vsc:: sess_fail_ebadf
+	:oneliner:	Session accept failures: bad file descriptor
+
+	Detailled reason for sess_fail: The listen socket file
+	descriptor was invalid. Should never happen.
+
+.. varnish_vsc:: sess_fail_enomem
+	:oneliner:	Session accept failures: not enough memory
+
+	Detailled reason for sess_fail: Most likely insufficient
+	socket buffer memory. Should never happen
+
+.. varnish_vsc:: sess_fail_other
+	:oneliner:	Session accept failures: other
+
+	Detailled reason for sess_fail: neither of the above, see
+	Debug log (varnishlog -g raw -I Debug:^Accept).
 
 .. varnish_vsc:: client_req_400
 	:oneliner:	Client requests received, subject to 400 errors
diff --git a/bin/varnishd/cache/cache_acceptor.c b/bin/varnishd/cache/cache_acceptor.c
index 6973d01d8..455697fe1 100644
--- a/bin/varnishd/cache/cache_acceptor.c
+++ b/bin/varnishd/cache/cache_acceptor.c
@@ -489,23 +489,32 @@ vca_accept_task(struct worker *wrk, void *arg)
 		if (i < 0) {
 			switch (errno) {
 			case ECONNABORTED:
+				wrk->stats->sess_fail_econnaborted++;
+				break;
+			case EINTR:
+				wrk->stats->sess_fail_eintr++;
 				break;
 			case EMFILE:
-				VSL(SLT_Debug, ls->sock, "Too many open files");
+				wrk->stats->sess_fail_emfile++;
 				vca_pace_bad();
 				break;
 			case EBADF:
-				VSL(SLT_Debug, ls->sock, "Accept failed: %s",
-				    strerror(errno));
+				wrk->stats->sess_fail_ebadf++;
+				vca_pace_bad();
+				break;
+			case ENOBUFS:
+			case ENOMEM:
+				wrk->stats->sess_fail_enomem++;
 				vca_pace_bad();
 				break;
 			default:
-				VSL(SLT_Debug, ls->sock, "Accept failed: %s",
-				    strerror(errno));
+				wrk->stats->sess_fail_other++;
 				vca_pace_bad();
 				break;
 			}
 			wrk->stats->sess_fail++;
+			VSL(SLT_Debug, ls->sock, "Accept failed: %s",
+			    strerror(errno));
 			(void)Pool_TrySumstat(wrk);
 			continue;
 		}
diff --git a/doc/changes.rst b/doc/changes.rst
index fd1b498ed..81b7d0a6f 100644
--- a/doc/changes.rst
+++ b/doc/changes.rst
@@ -31,6 +31,21 @@ release process.
 Varnish Cache 6.0.1 (ongoing)
 ================================
 
+varnishstat
+-----------
+
+* The counters
+
+  * ``sess_fail_econnaborted``
+  * ``sess_fail_eintr``
+  * ``sess_fail_emfile``
+  * ``sess_fail_ebadf``
+  * ``sess_fail_enomem``
+  * ``sess_fail_other``
+
+  now break down the detailled reason for session accept failures, the
+  sum of which continues to be counted in ``sess_fail``.
+
 VCL and bundled VMODs
 ---------------------