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

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

We already have a logging capability in xenconsoled, albeit enabled globally
via a command-line switch and no direct control over log-file naming. But do
we really need a second method?

 K.

On 20/05/2010 13:08, "Ian Campbell" <ian.campbell@xxxxxxxxxx> wrote:

> 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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> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel



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