[Xen-devel] [PATCH] xenconsoled: add ability to log guest consoles

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

This is useful as a debugging aid when guests die too quickly to catch
their console or produce so much spew that the ring has been recycled
etc.

Logging is enable by writing the filename of the logfile to the node
/local/logconsole/<domid> in xenstore.

Writing the empty string or removing the node stops logging.

Writing the same path to the node causes the daemon to close and
reopen the file -- this can be used to logrotate the file.

The /local/logconsole directory should not be removed as otherwise all
console logging will not work until xenconsoled is restarted.

Logging can also be enabled by writing a filename containing %d to the
node /local/logconsole/@ in xenstore.  This enables logging for
domains for which no /local/logconsole/<domid> node exists.  The
filename is expanded by replacing %d with the domain id.

Original patch by Christian Limpach.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

diff -r 2c5201796a2c -r 4997d5743bc3 tools/console/daemon/io.c
--- a/tools/console/daemon/io.c Thu May 20 12:55:56 2010 +0100
+++ b/tools/console/daemon/io.c Thu May 20 13:07:25 2010 +0100
@@ -97,7 +97,11 @@
        struct xencons_interface *interface;
        int event_count;
        long long next_period;
+       FILE *logfile;
 };
+
+static void update_logconsole(struct domain *);
+static char *wildcard_logfile = NULL;
 
 static struct domain *dom_head;
 
@@ -152,6 +156,7 @@
        struct buffer *buffer = &dom->buffer;
        XENCONS_RING_IDX cons, prod, size;
        struct xencons_interface *intf = dom->interface;
+       size_t begin;
 
        cons = intf->out_cons;
        prod = intf->out_prod;
@@ -170,9 +175,15 @@
                }
        }
 
+       begin = buffer->size;
        while (cons != prod)
                buffer->data[buffer->size++] = intf->out[
                        MASK_XENCONS_IDX(cons++, intf->out)];
+       if (dom->logfile && buffer->size != begin) {
+               fwrite(&buffer->data[begin], buffer->size - begin, 1,
+                      dom->logfile);
+               fflush(dom->logfile);
+       }
 
        xen_mb();
        intf->out_cons = cons;
@@ -699,6 +710,9 @@
        if (!watch_domain(dom, true))
                goto out;
 
+       dom->logfile = NULL;
+       update_logconsole(dom);
+
        dom->next = dom_head;
        dom_head = dom;
 
@@ -725,12 +739,17 @@
 static void remove_domain(struct domain *dom)
 {
        struct domain **pp;
+       FILE *oldfile;
 
        dolog(LOG_DEBUG, "Removing domain-%d", dom->domid);
 
        for (pp = &dom_head; *pp; pp = &(*pp)->next) {
                if (dom == *pp) {
                        *pp = dom->next;
+                       oldfile = dom->logfile;
+                       dom->logfile = NULL;
+                       if (oldfile)
+                               fclose(oldfile);
                        free(dom);
                        break;
                }
@@ -782,6 +801,36 @@
                }
                domid = dominfo.domid + 1;
        }
+}
+
+static void update_logconsole(struct domain *dom)
+{
+       char *fname = NULL, *path = NULL;
+       FILE *oldfile;
+
+       oldfile = dom->logfile;
+
+       if (asprintf(&path, "/local/logconsole/%d", dom->domid) == -1)
+               goto out;
+
+       fname = xs_read(xs, XBT_NULL, path, NULL);
+       if (!fname && wildcard_logfile)
+               asprintf(&fname, wildcard_logfile, dom->domid);
+       if (!fname || !fname[0])
+               goto out;
+
+       dom->logfile = fopen(fname, "a");
+       if (!dom->logfile)
+               dolog(LOG_ERR, "fopen %s failed", fname);
+
+ out:
+       if (oldfile && dom->logfile == oldfile) {
+               dom->logfile = NULL;
+               fclose(oldfile);
+       }
+       free(fname);
+       free(path);
+       return;
 }
 
 static int ring_free_bytes(struct domain *dom)
@@ -909,6 +958,19 @@
                   been removed, so dom may be NULL here. */
                if (dom && dom->is_dead == false)
                        domain_create_ring(dom);
+       } else if (!strcmp(vec[XS_WATCH_TOKEN], "logconsole")) {
+               if (sscanf(vec[XS_WATCH_PATH], "/local/logconsole/%u",
+                          &domid) == 1) {
+                       dom = lookup_domain(domid);
+                       if (dom && dom->is_dead == false)
+                               update_logconsole(dom);
+               } else if (!strcmp(vec[XS_WATCH_PATH],
+                                  "/local/logconsole/@")) {
+                       free(wildcard_logfile);
+                       wildcard_logfile = xs_read(xs, XBT_NULL,
+                                                  "/local/logconsole/@",
+                                                  NULL);
+               }
        }
 
        free(vec);
@@ -1128,6 +1190,17 @@
        log_hv_evtchn = -1;
 }
 
+void watch_logconsole(void)
+{
+      bool success;
+
+      success = xs_watch(xs, "/local/logconsole", "logconsole");
+      if (!success)
+              dolog(LOG_ERR, "logconsole watch failed");
+      wildcard_logfile = xs_read(xs, XBT_NULL, "/local/logconsole/@", NULL);
+}
+
+
 /*
  * Local variables:
  *  c-file-style: "linux"
diff -r 2c5201796a2c -r 4997d5743bc3 tools/console/daemon/io.h
--- a/tools/console/daemon/io.h Thu May 20 12:55:56 2010 +0100
+++ b/tools/console/daemon/io.h Thu May 20 13:07:25 2010 +0100
@@ -23,5 +23,6 @@
 
 void enum_domains(void);
 void handle_io(void);
+void watch_logconsole(void);
 
 #endif
diff -r 2c5201796a2c -r 4997d5743bc3 tools/console/daemon/main.c
--- a/tools/console/daemon/main.c       Thu May 20 12:55:56 2010 +0100
+++ b/tools/console/daemon/main.c       Thu May 20 13:07:25 2010 +0100
@@ -159,6 +159,8 @@
        if (!xen_setup())
                exit(1);
 
+       watch_logconsole();
+
        enum_domains();
 
        handle_io();

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