init: don't use fixed size buffer for command

We store init actions forever. 256 bytes per action means that
a typical inittab of ~10 commands uses 2.5k just to remember
command strings - which are usually _much_ shorter than 256 bytes.

At a cost of a bit more code, it's possible to allocate
only actually needed amount.

function                                             old     new   delta
init_exec                                            224     248     +24
new_init_action                                      140     142      +2

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/init/init.c b/init/init.c
index f3a35d5..05ed4f7 100644 (file)
--- a/init/init.c
+++ b/init/init.c
@@ -140,7 +140,6 @@
  * not fully functional init by switching it on! */
 #define DEBUG_INIT 0
 
-#define COMMAND_SIZE      256
 #define CONSOLE_NAME_SIZE 32
 
 /* Default sysinit script. */
@@ -195,7 +194,7 @@ struct init_action {
        pid_t pid;
        uint8_t action_type;
        char terminal[CONSOLE_NAME_SIZE];
-       char command[COMMAND_SIZE];
+       char command[1];
 };
 
 static struct init_action *init_action_list = NULL;
@@ -398,7 +397,7 @@ static void reset_sighandlers_and_unblock_sigs(void)
 }
 
 /* Wrapper around exec:
- * Takes string (max COMMAND_SIZE chars).
+ * Takes string.
  * If chars like '>' detected, execs '[-]/bin/sh -c "exec ......."'.
  * Otherwise splits words on whitespace, deals with leading dash,
  * and uses plain exec().
@@ -406,10 +405,15 @@ static void reset_sighandlers_and_unblock_sigs(void)
  */
 static void init_exec(const char *command)
 {
-       char *cmd[COMMAND_SIZE / 2];
-       char buf[COMMAND_SIZE + 6];  /* COMMAND_SIZE+strlen("exec ")+1 */
-       int dash = (command[0] == '-' /* maybe? && command[1] == '/' */);
-
+       /* +8 allows to write VLA sizes below more efficiently: */
+       unsigned command_size = strlen(command) + 8;
+       /* strlen(command) + strlen("exec ")+1: */
+       char buf[command_size];
+       /* strlen(command) / 2 + 4: */
+       char *cmd[command_size / 2];
+       int dash;
+
+       dash = (command[0] == '-' /* maybe? && command[1] == '/' */);
        command += dash;
 
        /* See if any special /bin/sh requiring characters are present */
@@ -626,13 +630,13 @@ static void new_init_action(uint8_t action_type, const char *command, const char
                nextp = &a->next;
        }
 
-       a = xzalloc(sizeof(*a));
+       a = xzalloc(sizeof(*a) + strlen(command));
 
        /* Append to the end of the list */
  append:
        *nextp = a;
        a->action_type = action_type;
-       safe_strncpy(a->command, command, sizeof(a->command));
+       strcpy(a->command, command);
        safe_strncpy(a->terminal, cons, sizeof(a->terminal));
        dbg_message(L_LOG | L_CONSOLE, "command='%s' action=%d tty='%s'\n",
                a->command, a->action_type, a->terminal);