conf: add 'tweak.pty-prefetch-buffer-size-kb' setting

This controls the size of the buffers used by the PTY reader
thread. The default is 512KB, for now.

config.c

@@ -657,6 +657,18 @@ parse_section_tweak(
                  conf->tweak.max_shm_pool_size);
     }
 
+    else if (strcmp(key, "pty-prefetch-buffer-size-kb") == 0) {
+        unsigned long kb;
+        if (!str_to_ulong(value, 10, &kb)) {
+            LOG_ERR("%s:%d: expected an integer: %s", path, lineno, value);
+            return false;
+        }
+
+        conf->tweak.pty_prefetch_size = min(kb * 1024, UINT32_MAX);
+        LOG_WARN("tweak: pty-prefetch-buffer-size=%u bytes",
+                 conf->tweak.pty_prefetch_size);
+    }
+
     else {
         LOG_ERR("%s:%u: invalid key: %s", path, lineno, key);
         return false;
@@ -930,6 +942,7 @@ config_load(struct config *conf, const char *conf_path)
             .delayed_render_lower_ns = 500000,         /* 0.5ms */
             .delayed_render_upper_ns = 16666666 / 2,   /* half a frame period (60Hz) */
             .max_shm_pool_size = 512 * 1024 * 1024,
+            .pty_prefetch_size = 512 * 1024,
         },
     };
 

config.h

@@ -81,6 +81,7 @@ struct config {
         uint64_t delayed_render_lower_ns;
         uint64_t delayed_render_upper_ns;
         off_t max_shm_pool_size;
+        unsigned pty_prefetch_size;
     } tweak;
 };
 

terminal.c

@@ -317,12 +317,6 @@ ptmx_reader_thread(void *_term)
                     amount = term->ptmx_read_buffer.size - len;
                 }
 
-                /* TODO */
-                if (amount == 0) {
-                    LOG_ERR("PTY read buffer full");
-                    abort();
-                }
-
                 ssize_t count = read(term->ptmx, &buf[len], amount);
                 if (count < 0) {
                     LOG_ERRNO("failed to read from PTY");
@@ -904,10 +898,10 @@ term_init(const struct config *conf, struct fdm *fdm, struct reaper *reaper,
         .ptmx_read_buffer = {
             .event_fd = ptmx_event_fd,
             .idx = 0,
-            .size = 4 * 1024 * 1024,
+            .size = conf->tweak.pty_prefetch_size,
             .buf = {
-                {.data = malloc(4 * 1024 * 1024), .len = 0},
+                {.data = malloc(conf->tweak.pty_prefetch_size), .len = 0},
-                {.data = malloc(4 * 1024 * 1024), .len = 0},
+                {.data = malloc(conf->tweak.pty_prefetch_size), .len = 0},
             },
         },
         .ptmx_buffer = tll_init(),

terminal.h

@@ -215,12 +215,12 @@ struct terminal {
         mtx_t lock;
         cnd_t cond;
         int event_fd;
-        int size;
+        unsigned size;
 
         uint8_t idx;
         struct {
             uint8_t *data;
-            int len;
+            unsigned len;
         } buf[2];
     } ptmx_read_buffer;