MINOR: promex: use watcher to iterate over backend instances

Ensures proxies iteration in promex applet is safe via a new watcher
member. The principle is similar to the one already used for servers
iteration.

Note that ctx.p[0] is not updated anymore at the end of a function, as
this is automatically done via the watcher itself.

diff --git a/addons/promex/service-prometheus.c b/addons/promex/service-prometheus.c
index 9196c9d6264bd8bd038f81932c60d25b8e7199ed..a792fed998ff5074e3febdfeb96da151bad8888c 100644 (file)
--- a/addons/promex/service-prometheus.c
+++ b/addons/promex/service-prometheus.c
@@ -83,6 +83,7 @@ struct promex_ctx {
        unsigned field_num;        /* current field number (ST_I_PX_* etc) */
        unsigned mod_field_num;    /* first field number of the current module (ST_I_PX_* etc) */
        int obj_state;             /* current state among PROMEX_{FRONT|BACK|SRV|LI}_STATE_* */
+       struct watcher px_watch;   /* watcher to automatically update next pointer */
        struct watcher srv_watch;  /* watcher to automatically update next pointer */
        struct list modules;       /* list of promex modules to export */
        struct eb_root filters;    /* list of filters to apply on metrics name */
@@ -940,9 +941,6 @@ static int promex_dump_back_metrics(struct appctx *appctx, struct htx *htx)
                if (promex_filter_metric(appctx, prefix, name))
                        continue;
 
-               if (!px)
-                       px = proxies_list;
-
                while (px) {
                        struct promex_label labels[PROMEX_MAX_LABELS-1] = {};
                        unsigned int srv_state_count[PROMEX_SRV_STATE_COUNT] = { 0 };
@@ -1097,9 +1095,16 @@ static int promex_dump_back_metrics(struct appctx *appctx, struct htx *htx)
                                            &val, labels, &out, max))
                                goto full;
                  next_px:
-                       px = px->next;
+                       px = watcher_next(&ctx->px_watch, px->next);
                }
+               watcher_detach(&ctx->px_watch);
                ctx->flags |= PROMEX_FL_METRIC_HDR;
+
+               /* Prepare a new iteration for the next stat column.
+                * Update ctx.p[0] via watcher.
+                */
+               watcher_attach(&ctx->px_watch, proxies_list);
+               px = proxies_list;
        }
 
        /* Skip extra counters */
@@ -1122,9 +1127,6 @@ static int promex_dump_back_metrics(struct appctx *appctx, struct htx *htx)
                        if (promex_filter_metric(appctx, prefix, name))
                                continue;
 
-                       if (!px)
-                               px = proxies_list;
-
                        while (px) {
                                struct promex_label labels[PROMEX_MAX_LABELS-1] = {};
                                struct promex_metric metric;
@@ -1159,25 +1161,39 @@ static int promex_dump_back_metrics(struct appctx *appctx, struct htx *htx)
                                        goto full;
 
                        next_px2:
-                               px = px->next;
+                               px = watcher_next(&ctx->px_watch, px->next);
                        }
+                       watcher_detach(&ctx->px_watch);
                        ctx->flags |= PROMEX_FL_METRIC_HDR;
+
+                       /* Prepare a new iteration for the next stat column.
+                        * Update ctx.p[0] via watcher.
+                        */
+                       watcher_attach(&ctx->px_watch, proxies_list);
+                       px = proxies_list;
                }
 
                ctx->field_num += mod->stats_count;
                ctx->mod_field_num = 0;
        }
 
-       px = NULL;
-       mod = NULL;
-
   end:
+       if (ret) {
+               watcher_detach(&ctx->px_watch);
+               mod = NULL;
+       }
+
        if (out.len) {
-               if (!htx_add_data_atonce(htx, out))
+               if (!htx_add_data_atonce(htx, out)) {
+                       watcher_detach(&ctx->px_watch);
                        return -1; /* Unexpected and unrecoverable error */
+               }
        }
-       /* Save pointers (0=current proxy, 1=current stats module) of the current context */
-       ctx->p[0] = px;
+
+       /* Save pointers of the current context for dump resumption :
+        * 0=current proxy, 1=current stats module
+        * Note that p[0] is already automatically updated via px_watch.
+        */
        ctx->p[1] = mod;
        return ret;
   full:
@@ -1393,19 +1409,22 @@ static int promex_dump_srv_metrics(struct appctx *appctx, struct htx *htx)
 
                  next_px:
                        watcher_detach(&ctx->srv_watch);
-                       px = px->next;
+                       px = watcher_next(&ctx->px_watch, px->next);
                        if (px) {
                                /* Update ctx.p[1] via watcher. */
                                watcher_attach(&ctx->srv_watch, px->srv);
                                sv = ctx->p[1];
                        }
                }
+               watcher_detach(&ctx->px_watch);
                ctx->flags |= PROMEX_FL_METRIC_HDR;
 
-               /* Prepare a new iteration for the next stat column. */
+               /* Prepare a new iteration for the next stat column.
+                * Update ctx.p[0]/p[1] via px_watch/srv_watch.
+                */
+               watcher_attach(&ctx->px_watch, proxies_list);
                px = proxies_list;
                if (likely(px)) {
-                       /* Update ctx.p[1] via watcher. */
                        watcher_attach(&ctx->srv_watch, px->srv);
                        sv = ctx->p[1];
                }
@@ -1478,19 +1497,22 @@ static int promex_dump_srv_metrics(struct appctx *appctx, struct htx *htx)
 
                          next_px2:
                                watcher_detach(&ctx->srv_watch);
-                               px = px->next;
+                               px = watcher_next(&ctx->px_watch, px->next);
                                if (px) {
                                        /* Update ctx.p[1] via watcher. */
                                        watcher_attach(&ctx->srv_watch, px->srv);
                                        sv = ctx->p[1];
                                }
                        }
+                       watcher_detach(&ctx->px_watch);
                        ctx->flags |= PROMEX_FL_METRIC_HDR;
 
-                       /* Prepare a new iteration for the next stat column. */
+                       /* Prepare a new iteration for the next stat column.
+                        * Update ctx.p[0]/p[1] via px_watch/srv_watch.
+                        */
+                       watcher_attach(&ctx->px_watch, proxies_list);
                        px = proxies_list;
                        if (likely(px)) {
-                               /* Update ctx.p[1] via watcher. */
                                watcher_attach(&ctx->srv_watch, px->srv);
                                sv = ctx->p[1];
                        }
@@ -1502,8 +1524,8 @@ static int promex_dump_srv_metrics(struct appctx *appctx, struct htx *htx)
 
   end:
        if (ret) {
+               watcher_detach(&ctx->px_watch);
                watcher_detach(&ctx->srv_watch);
-               px = NULL;
                mod = NULL;
        }
 
@@ -1514,9 +1536,8 @@ static int promex_dump_srv_metrics(struct appctx *appctx, struct htx *htx)
 
        /* Save pointers of the current context for dump resumption :
         * 0=current proxy, 1=current server, 2=current stats module
-        * Note that p[1] is already automatically updated via srv_watch.
+        * Note that p[0]/p[1] are already automatically updated via px_watch/srv_watch.
         */
-       ctx->p[0] = px;
        ctx->p[2] = mod;
        return ret;
   full:
@@ -1524,6 +1545,7 @@ static int promex_dump_srv_metrics(struct appctx *appctx, struct htx *htx)
        goto end;
 
   error:
+       watcher_detach(&ctx->px_watch);
        watcher_detach(&ctx->srv_watch);
        return -1;
 }
@@ -1746,6 +1768,11 @@ static int promex_dump_metrics(struct appctx *appctx, struct htx *htx)
                        ctx->field_num = ST_I_PX_PXNAME;
                        ctx->mod_field_num = 0;
                        appctx->st1 = PROMEX_DUMPER_BACK;
+
+                       if (ctx->flags & PROMEX_FL_SCOPE_BACK) {
+                               /* Update ctx.p[0] via watcher. */
+                               watcher_attach(&ctx->px_watch, proxies_list);
+                       }
                        __fallthrough;
 
                case PROMEX_DUMPER_BACK:
@@ -1765,7 +1792,8 @@ static int promex_dump_metrics(struct appctx *appctx, struct htx *htx)
                        appctx->st1 = PROMEX_DUMPER_SRV;
 
                        if (ctx->flags & PROMEX_FL_SCOPE_SERVER) {
-                               ctx->p[0] = proxies_list;
+                               /* Update ctx.p[0] via watcher. */
+                               watcher_attach(&ctx->px_watch, proxies_list);
                                if (likely(proxies_list)) {
                                        /* Update ctx.p[1] via watcher. */
                                        watcher_attach(&ctx->srv_watch, proxies_list->srv);
@@ -2048,6 +2076,7 @@ static int promex_appctx_init(struct appctx *appctx)
        LIST_INIT(&ctx->modules);
        ctx->filters = EB_ROOT;
        appctx->st0 = PROMEX_ST_INIT;
+       watcher_init(&ctx->px_watch,  &ctx->p[0], offsetof(struct proxy,  watcher_list));
        watcher_init(&ctx->srv_watch, &ctx->p[1], offsetof(struct server, watcher_list));
        return 0;
 }
@@ -2062,6 +2091,11 @@ static void promex_appctx_release(struct appctx *appctx)
        struct promex_metric_filter *flt;
         struct eb32_node *node, *next;
 
+       if (appctx->st1 == PROMEX_DUMPER_BACK ||
+           appctx->st1 == PROMEX_DUMPER_SRV) {
+               watcher_detach(&ctx->px_watch);
+       }
+
        if (appctx->st1 == PROMEX_DUMPER_SRV)
                watcher_detach(&ctx->srv_watch);