[lxc-devel] API errors

[Serge Hallyn]

Quoting Serge Hallyn (serge.hallyn at ubuntu.com):
> Quoting S.Çağlar Onur (caglar at 10ur.org):
> > Hi,
> > 
> > src/lxc/lxccontainer.h contains two public field named error_string and
> > error_num. If I'm not missing anything no one seems to be using them.
> > 
> > What was the intention? Should API calls set those and stop using macros
> > like ERROR and SYSERROR?
> 
> That is the idea.  It's not yet clear to me how to best track that.
> Maybe it should become an array of strings, so that each stack layer
> moving up and seeing an error happened can give its own input on what
> it was doing.  Then when lxc-start fails, we can see something like
> 
> 	[0] failed to create container
> 	[1] failed to setup network
> 	[2] failed to create veth
> 	[3] failed to pass veth into network namespce
> 
> And then yes, ERROR and SYSERROR should be reserved for the actual
> programs, and should spit out error stacks as well.

So I'm thinking an API like the below.  Much in bdev.c for instance can
be converted to PUSH_ERR.  Although all the places where we have
fork()ed obviouslly cannot.  There they'll have to keep doing ERROR(),
and the parent can point to the logfile for further info.

diff --git a/src/lxc/lxccontainer.h b/src/lxc/lxccontainer.h
index 20ab8e8..b3c9641 100644
--- a/src/lxc/lxccontainer.h
+++ b/src/lxc/lxccontainer.h
@@ -49,9 +49,16 @@ struct lxc_container {
 	int numthreads; /* protected by privlock. */
 	struct lxc_conf *lxc_conf; // maybe we'll just want the whole lxc_handler?
 
-	// public fields
-	char *error_string;
+	// error stack - protected by privlock
+	// These can be accessed using get_errors() and clear_errors()
+	// below.
+	char **error_string;
 	int error_num;
+	bool oom;  // true if there were more errors but no free memory;
+	char oom_error[MAXPATHLEN];  // if we oomed, last error goes in here
+
+	// public fields
+	bool
 	int daemonize;
 
 	char *config_path;
@@ -229,6 +236,18 @@ struct lxc_container {
 	 * and the caller may not access it.  Return true otherwise.
 	 */
 	bool (*may_control)(struct lxc_container *c);
+
+	/*
+	 * Get stack of errors - one per line
+	 * @output: preallocated string into which to print the errors
+	 * @inlen: the length of passed-in buffer
+	 * @oomed: will be set to 1 if we also oomed, in which case the oom msg
+	 *         is also a part of @output.
+	 *
+	 * Returns the needed length (including terminating \0)
+	 */
+	int (*get_errors)(struct lxc_container *c, char *output, int inlen, int *oomed);
+	void (*clear_errors)();
 };
 
 struct lxc_snapshot {
@@ -248,6 +267,18 @@ const char *lxc_get_default_lvm_vg(void);
 const char *lxc_get_default_zfs_root(void);
 const char *lxc_get_version(void);
 
+/*
+ * Add another error to c->error_string, bump error_num.  If we run
+ * out of memory and c->oom is not yet set, then set c->oom to 1 and
+ * put the message into c->oom_error.
+ */
+int DO_PUSH_ERR(struct lxc_container *c, char *fmt, ...);
+
+/*
+ * DO_PUSH_ERR_locked is same as DO_PUSH_ERR but will not call process_lock().
+ */
+int DO_PUSH_ERR_locked(struct lxc_container *c, char *fmt, ...);
+
 #if 0
 char ** lxc_get_valid_keys();
 char ** lxc_get_valid_values(char *key);