debug: add "ringbuf" backend logging to a ringbuffer

This is useful for debugging bugs that involve timing effects and are
not reproducible when logging at higher debug levels with the file
backend.

The log can be dumped to a file with gdb:

(gdb) dump binary memory samba.log debug_ringbuf debug_ringbuf+SIZE

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Volker Lendecke <vl@samba.org>

diff --git a/docs-xml/smbdotconf/logging/logging.xml b/docs-xml/smbdotconf/logging/logging.xml
index 8524884bbffd1c26542573b3e93ddc2bb1f27faf..b152d0c469e83f682418595992353f9d861a6cca 100644 (file)
--- a/docs-xml/smbdotconf/logging/logging.xml
+++ b/docs-xml/smbdotconf/logging/logging.xml
@@ -31,8 +31,13 @@
     <listitem><para><parameter moreinfo="none">systemd</parameter></para></listitem>
     <listitem><para><parameter moreinfo="none">lttng</parameter></para></listitem>
     <listitem><para><parameter moreinfo="none">gpfs</parameter></para></listitem>
+    <listitem><para><parameter moreinfo="none">ringbuf</parameter></para></listitem>
   </itemizedlist>
 
+  <para>The <parameter moreinfo="none">ringbuf</parameter> backend supports an
+  optional size argument to change the buffer size used, the default is 1 MB:
+  <parameter moreinfo="none">ringbuf:size=NBYTES</parameter></para>
+
 </description>
 <value type="default"></value>
 <value type="example">syslog@1 file</value>

diff --git a/lib/util/debug.c b/lib/util/debug.c
index 12a9b1bcaaaf8fad17830ba8a15857b74e1e46a8..08954c30fdeaee200a672403af4898ab2eb275a4 100644 (file)
--- a/lib/util/debug.c
+++ b/lib/util/debug.c
@@ -236,6 +236,84 @@ static void debug_gpfs_log(int msg_level,
 }
 #endif /* HAVE_GPFS */
 
+#define DEBUG_RINGBUF_SIZE (1024 * 1024)
+#define DEBUG_RINGBUF_SIZE_OPT "size="
+
+static char *debug_ringbuf;
+static size_t debug_ringbuf_size;
+static size_t debug_ringbuf_ofs;
+
+/* We ensure in debug_ringbuf_log() that this is always \0 terminated */
+char *debug_get_ringbuf(void)
+{
+       return debug_ringbuf;
+}
+
+/* Return the size of the ringbuf (including a \0 terminator) */
+size_t debug_get_ringbuf_size(void)
+{
+       return debug_ringbuf_size;
+}
+
+static void debug_ringbuf_reload(bool enabled, bool previously_enabled,
+                                const char *prog_name, char *option)
+{
+       bool cmp;
+       size_t optlen = strlen(DEBUG_RINGBUF_SIZE_OPT);
+
+       debug_ringbuf_size = DEBUG_RINGBUF_SIZE;
+       debug_ringbuf_ofs = 0;
+
+       SAFE_FREE(debug_ringbuf);
+
+       if (!enabled) {
+               return;
+       }
+
+       if (option != NULL) {
+               cmp = strncmp(option, DEBUG_RINGBUF_SIZE_OPT, optlen);
+               if (cmp == 0) {
+                       debug_ringbuf_size = (size_t)strtoull(
+                               option + optlen, NULL, 10);
+               }
+       }
+
+       debug_ringbuf = calloc(debug_ringbuf_size, sizeof(char));
+       if (debug_ringbuf == NULL) {
+               return;
+       }
+}
+
+static void debug_ringbuf_log(int msg_level,
+                             const char *msg,
+                             const char *msg_no_nl)
+{
+       size_t msglen = strlen(msg);
+       size_t allowed_size;
+
+       if (debug_ringbuf == NULL) {
+               return;
+       }
+
+       /* Ensure the buffer is always \0 terminated */
+       allowed_size = debug_ringbuf_size - 1;
+
+       if (msglen > allowed_size) {
+               return;
+       }
+
+       if ((debug_ringbuf_ofs + msglen) < debug_ringbuf_ofs) {
+               return;
+       }
+
+       if ((debug_ringbuf_ofs + msglen) > allowed_size) {
+               debug_ringbuf_ofs = 0;
+       }
+
+       memcpy(debug_ringbuf + debug_ringbuf_ofs, msg, msglen);
+       debug_ringbuf_ofs += msglen;
+}
+
 static struct debug_backend {
        const char *name;
        int log_level;
@@ -278,6 +356,11 @@ static struct debug_backend {
                .log = debug_gpfs_log,
        },
 #endif
+       {
+               .name = "ringbuf",
+               .log = debug_ringbuf_log,
+               .reload = debug_ringbuf_reload,
+       },
 };
 
 static struct debug_backend *debug_find_backend(const char *name)

diff --git a/lib/util/debug.h b/lib/util/debug.h
index b50bf50266238742cdf70575b4255c293d9022df..43c6aa08c7669ae1216ff9851e928a1b0e1694a8 100644 (file)
--- a/lib/util/debug.h
+++ b/lib/util/debug.h
@@ -287,4 +287,7 @@ typedef void (*debug_callback_fn)(void *private_ptr, int level, const char *msg)
  */
 void debug_set_callback(void *private_ptr, debug_callback_fn fn);
 
+char *debug_get_ringbuf(void);
+size_t debug_get_ringbuf_size(void);
+
 #endif /* _SAMBA_DEBUG_H */