From 5b8bf5d4130761c3374f9ad618e8a76bb75eb634 Mon Sep 17 00:00:00 2001
From: Yuwei Ba <i@xiaoba.me>
Date: Fri, 21 Aug 2020 15:06:10 +0800
Subject: [PATCH] snmpd: support MemAvailable on Linux

See also https://github.com/net-snmp/net-snmp/pull/167 .

[bvanassche: modified the behavior of this patch]
---
 agent/mibgroup/hardware/memory/memory_linux.c | 20 ++++++++++++++++++-
 agent/mibgroup/ucd-snmp/memory.c              | 12 ++++++++++-
 agent/mibgroup/ucd-snmp/memory.h              |  1 +
 include/net-snmp/agent/hardware/memory.h      |  1 +
 mibs/UCD-SNMP-MIB.txt                         | 16 +++++++++++++++
 5 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/agent/mibgroup/hardware/memory/memory_linux.c b/agent/mibgroup/hardware/memory/memory_linux.c
index 6d5e86cde4..4ae235c2d0 100644
--- a/agent/mibgroup/hardware/memory/memory_linux.c
+++ b/agent/mibgroup/hardware/memory/memory_linux.c
@@ -24,7 +24,8 @@ int netsnmp_mem_arch_load( netsnmp_cache *cache, void *magic ) {
     static int   first = 1;
     ssize_t      bytes_read;
     char        *b;
-    unsigned long memtotal = 0,  memfree = 0, memshared = 0,
+    int          have_memavail = 0;
+    unsigned long memtotal = 0,  memavail = 0, memfree = 0, memshared = 0,
                   buffers = 0,   cached = 0, sreclaimable = 0,
                   swaptotal = 0, swapfree = 0;
 
@@ -81,6 +82,11 @@ int netsnmp_mem_arch_load( netsnmp_cache *cache, void *magic ) {
         if (first)
             snmp_log(LOG_ERR, "No MemTotal line in /proc/meminfo\n");
     }
+    b = strstr(buff, "MemAvailable: ");
+    if (b) {
+        have_memavail = 1;
+        sscanf(b, "MemAvailable: %lu", &memavail);
+    }
     b = strstr(buff, "MemFree: ");
     if (b) 
         sscanf(b, "MemFree: %lu", &memfree);
@@ -151,6 +157,18 @@ int netsnmp_mem_arch_load( netsnmp_cache *cache, void *magic ) {
         mem->other = -1;
     }
 
+    if (have_memavail) {
+        mem = netsnmp_memory_get_byIdx(NETSNMP_MEM_TYPE_AVAILMEM, 1);
+        if (mem) {
+            if (!mem->descr)
+                mem->descr = strdup("Available memory");
+            mem->units = 1024;
+            mem->size  = memavail;
+            mem->free  = memavail;
+            mem->other = -1;
+        }
+    }
+
     mem = netsnmp_memory_get_byIdx( NETSNMP_MEM_TYPE_VIRTMEM, 1 );
     if (!mem) {
         snmp_log_perror("No Virtual Memory info entry");
diff --git a/agent/mibgroup/ucd-snmp/memory.c b/agent/mibgroup/ucd-snmp/memory.c
index 371a77e9a5..158b28e67b 100644
--- a/agent/mibgroup/ucd-snmp/memory.c
+++ b/agent/mibgroup/ucd-snmp/memory.c
@@ -26,7 +26,7 @@ init_memory(void)
         netsnmp_create_handler_registration("memory", handle_memory,
                                  memory_oid, OID_LENGTH(memory_oid),
                                              HANDLER_CAN_RONLY),
-                                 1, 26);
+                                 1, 27);
     netsnmp_register_scalar(
         netsnmp_create_handler_registration("memSwapError", handle_memory,
                            memSwapError_oid, OID_LENGTH(memSwapError_oid),
@@ -272,6 +272,16 @@ handle_memory(netsnmp_mib_handler *handler,
 	    c64.low = val & 0xFFFFFFFF;
 	    c64.high = val >>32;
             break;
+        case MEMORY_SYS_AVAIL:
+	    type = ASN_COUNTER64;
+            mem_info = netsnmp_memory_get_byIdx(NETSNMP_MEM_TYPE_AVAILMEM, 0);
+            if (!mem_info)
+                goto NOSUCH;
+            val = mem_info->size;       /* memavail */
+            val *= (mem_info->units/1024);
+	    c64.low = val & 0xFFFFFFFF;
+	    c64.high = val >> 32;
+            break;
         case MEMORY_SWAP_ERROR:
             mem_info = netsnmp_memory_get_byIdx( NETSNMP_MEM_TYPE_SWAP, 0 );
             if (!mem_info)
diff --git a/agent/mibgroup/ucd-snmp/memory.h b/agent/mibgroup/ucd-snmp/memory.h
index ded2140227..54a56a2fdb 100644
--- a/agent/mibgroup/ucd-snmp/memory.h
+++ b/agent/mibgroup/ucd-snmp/memory.h
@@ -41,6 +41,7 @@ Netsnmp_Node_Handler handle_memory;
 #define MEMORY_SHARED_X     24
 #define MEMORY_BUFFER_X     25
 #define MEMORY_CACHED_X     26
+#define MEMORY_SYS_AVAIL    27
 #define MEMORY_SWAP_ERROR  100
 #define MEMORY_SWAP_ERRMSG 101
 #endif                          /* MEMORY_H */
diff --git a/include/net-snmp/agent/hardware/memory.h b/include/net-snmp/agent/hardware/memory.h
index 54265cf22a..aca3a4d00d 100644
--- a/include/net-snmp/agent/hardware/memory.h
+++ b/include/net-snmp/agent/hardware/memory.h
@@ -10,6 +10,7 @@ typedef struct netsnmp_memory_info_s netsnmp_memory_info;
 #define NETSNMP_MEM_TYPE_SHARED   8
 #define NETSNMP_MEM_TYPE_SHARED2  9
 #define NETSNMP_MEM_TYPE_SWAP    10
+#define NETSNMP_MEM_TYPE_AVAILMEM 11
     /* Leave space for individual swap devices */
 #define NETSNMP_MEM_TYPE_MAX     30
 
diff --git a/mibs/UCD-SNMP-MIB.txt b/mibs/UCD-SNMP-MIB.txt
index cde67feb50..d360bad025 100644
--- a/mibs/UCD-SNMP-MIB.txt
+++ b/mibs/UCD-SNMP-MIB.txt
@@ -746,6 +746,22 @@ memCachedX OBJECT-TYPE
          memory as specifically reserved for this purpose."
     ::= { memory 26 }
 
+memSysAvail OBJECT-TYPE
+    SYNTAX	CounterBasedGauge64
+    UNITS       "kB"
+    MAX-ACCESS	read-only
+    STATUS	current
+    DESCRIPTION
+        "The total amount of available memory, which is an estimate
+         of how much memory is available for starting new applications,
+         without swapping.
+
+         This object will not be implemented on hosts where the
+         underlying operating system does not explicitly identify
+         memory as specifically reserved for this purpose."
+    ::= { memory 27 }
+
+
 memSwapError OBJECT-TYPE
     SYNTAX	UCDErrorFlag
     MAX-ACCESS	read-only