tail: New keep_file_handle and fstat_interval_nsec options for tail input

plugins/in_tail/tail.c

@@ -78,7 +78,7 @@ static int in_tail_collect_pending(struct flb_input_instance *ins,
         if (file->watch_fd == -1 ||
             (file->offset >= file->size)) {
             /* Gather current file size */
-            ret = fstat(file->fd, &st);
+            ret = flb_tail_file_stat(file, &st);
             if (ret == -1) {
                 flb_errno();
                 flb_tail_file_remove(file);
@@ -343,7 +343,7 @@ int in_tail_collect_event(void *file, struct flb_config *config)
     struct stat st;
     struct flb_tail_file *f = file;
 
-    ret = fstat(f->fd, &st);
+    ret = flb_tail_file_stat(f, &st);
     if (ret == -1) {
         flb_tail_file_remove(f);
         return 0;
@@ -619,6 +619,13 @@ static struct flb_config_map config_map[] = {
      FLB_CONFIG_MAP_INT, "progress_check_interval_nsec", "0",
      0, FLB_TRUE, offsetof(struct flb_tail_config, progress_check_interval_nsec),
     },
+    {
+     FLB_CONFIG_MAP_STR, "fstat_interval", "250ms",
+     0, FLB_FALSE, 0,
+     "interval for fstat mode event polling. Controls how often files are checked "
+     "for changes when using stat-based file watching (instead of inotify). "
+     "Default is 250ms. Supports time suffixes: s, ms, us, ns."
+    },
     {
      FLB_CONFIG_MAP_TIME, "rotate_wait", FLB_TAIL_ROTATE_WAIT,
      0, FLB_TRUE, offsetof(struct flb_tail_config, rotate_wait),
@@ -719,7 +726,14 @@ static struct flb_config_map config_map[] = {
      0, FLB_TRUE, offsetof(struct flb_tail_config, skip_empty_lines),
      "Allows to skip empty lines."
     },
-
+    {
+     FLB_CONFIG_MAP_BOOL, "keep_file_handle", "true",
+     0, FLB_TRUE, offsetof(struct flb_tail_config, keep_file_handle),
+     "When set to false, the file handle will be reopened every time we read "
+     "from the source tailed file and closed when done, to avoid keeping it open. "
+     "Useful for SMB shares and network filesystems where keeping handles open "
+     "can cause issues."
+    },
     {
       FLB_CONFIG_MAP_BOOL, "truncate_long_lines", "false",
       0, FLB_TRUE, offsetof(struct flb_tail_config, truncate_long_lines),

plugins/in_tail/tail_config.c

@@ -106,6 +106,8 @@ struct flb_tail_config *flb_tail_config_create(struct flb_input_instance *ins,
     ctx->ins = ins;
     ctx->ignore_older = 0;
     ctx->skip_long_lines = FLB_FALSE;
+    ctx->keep_file_handle = FLB_TRUE;  /* default: keep file handle open */
+    ctx->fstat_interval_nsec = 250000000; /* default: 250ms */
 #ifdef FLB_HAVE_SQLDB
     ctx->db_sync = 1;  /* sqlite sync 'normal' */
 #endif
@@ -189,6 +191,47 @@ struct flb_tail_config *flb_tail_config_create(struct flb_input_instance *ins,
         }
     }
 
+    /* Config: fstat mode event polling interval */
+    tmp = flb_input_get_property("fstat_interval", ins);
+    if (tmp) {
+        /* Support suffixes: s, ms, us, ns; also allow plain seconds and fractional seconds */
+        char *end = NULL;
+        double val = strtod(tmp, &end);
+        uint64_t mult = 1000000000ULL; /* default: seconds */
+
+        if (end != NULL && *end != '\0') {
+            if (strcasecmp(end, "s") == 0)        mult = 1000000000ULL;
+            else if (strcasecmp(end, "ms") == 0)  mult = 1000000ULL;
+            else if (strcasecmp(end, "us") == 0)  mult = 1000ULL;
+            else if (strcasecmp(end, "ns") == 0)  mult = 1ULL;
+            else {
+                flb_plg_error(ctx->ins, "invalid 'fstat_interval' unit in value (%s)", tmp);
+                flb_tail_config_destroy(ctx);
+                return NULL;
+            }
+        }
+
+        if (val <= 0) {
+            flb_plg_error(ctx->ins, "invalid 'fstat_interval' value (%s)", tmp);
+            flb_tail_config_destroy(ctx);
+            return NULL;
+        }
+
+        /* Convert to nanoseconds with clamping to reasonable bounds */
+        double nsec_d = val * (double) mult;
+        if (nsec_d < 1.0) {
+            flb_plg_error(ctx->ins, "'fstat_interval' too small (%s)", tmp);
+            flb_tail_config_destroy(ctx);
+            return NULL;
+        }
+        ctx->fstat_interval_nsec = (uint64_t) nsec_d;
+
+        if (ctx->fstat_interval_nsec <= 1000000ULL) {
+            flb_plg_warn(ctx->ins, "very low fstat_interval (%" PRIu64 " ns) may cause high CPU usage",
+                         ctx->fstat_interval_nsec);
+        }
+    }
+
     /* Config: seconds interval to monitor file after rotation */
     if (ctx->rotate_wait <= 0) {
         flb_plg_error(ctx->ins, "invalid 'rotate_wait' config value");

plugins/in_tail/tail_config.h

@@ -107,6 +107,10 @@ struct flb_tail_config {
     int progress_check_interval;      /* watcher interval             */
     int progress_check_interval_nsec; /* watcher interval             */
 
+    uint64_t fstat_interval_nsec;     /* fstat mode event polling interval (nanoseconds) */
+
+    int keep_file_handle;      /* keep file handle open during tail (default: true) */
+
 #ifdef FLB_HAVE_INOTIFY
     int   inotify_watcher;     /* enable/disable inotify monitor */
 #endif