Re: [PATCH] ifplugd: repeated setenv calls

[Maksym Kryzhanovskyy]

> On Friday 07 May 2010 10:00, Maksym Kryzhanovskyy wrote:
> > > What we can do is to use the sequence
> > > 
> > > unsetenv(IFPLUGD_ENV_PREVIOUS);
> > > free(env_PREVIOUS);
> > > env_PREVIOUS = xasprintf(IFPLUGD_ENV_PREVIOUS"=%s",
> > > strstatus(G.iface_last_status));
> > > putenv(env_PREVIOUS);
> > > 
> > > every time we want to set the variable to the new value.
> > > env_PREVIOUS is a global variable of type char*.
> > > This will work correctly with any libc.
> > > 
> > > -- 
> > > vda
> > > 
> > 
> > Hi Denis,
> > 
> > thanks for your reply. I wrote two alternatives to
> > apply this technique. Please consider their usage.
> 
> ifplugd.setenv1.patch looks better. These lines are not needed:
> +       G.env_PREVIOUS = NULL; \
> +       G.env_CURRENT = NULL; \
> the rest is fine.
> 
> I applied a bit different version of it - I set/unset
> env just around spawn_and_wait(). See attached.
> 

Attached is a typo patch for IFPLUGD_ENV_CURRENT

> 
> ifplugd.setenv2.patch:
> 
> +       env = getenv(name);
> +       unsetenv(name);
> +       if (env != NULL) {
> +               free(env - strlen(name) - 1);
> +       }
> 
> Why do you think getenv result is safe to be freed?
> Initial program environment is NOT malloced,
> you must not free it, this may SEGV!

But when getenv returns non-null pointer it means
that the environment is allocated and var is found
in the table, or not? It also returns a pointer to
the previous block inserted by putenv().

+       env = getenv(name);
+       if (env != NULL) {
+               unsetenv(name);
+               free(env - strlen(name) - 1);
+       }

Valgrind is ok. Pointers are equal:

env_PREVIOUS = xasprintf("%s=%s", IFPLUGD_ENV_PREVIOUS, strstatus(G.iface_prev_status));
putenv(env_PREVIOUS);
env_CURRENT = xasprintf("%s=%s", IFPLUGD_ENV_CURRENT, strstatus(G.iface_last_status));
putenv(env_CURRENT);

bb_error_msg("%x:%x", env_PREVIOUS, getenv(IFPLUGD_ENV_PREVIOUS) - strlen(IFPLUGD_ENV_PREVIOUS) - 1);
bb_error_msg("%x:%x", env_CURRENT, getenv(IFPLUGD_ENV_CURRENT) - strlen(IFPLUGD_ENV_CURRENT) - 1);

> 
> -- 
> vda
> 
> 
> 
Max
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