Function sysctl_handle_string

freebsd/kern/kern_sysctl.c:1733–1806

 */

int
sysctl_handle_string(SYSCTL_HANDLER_ARGS)
{
	char *tmparg;
	size_t outlen;
	int error = 0, ro_string = 0;

	/*
	 * If the sysctl isn't writable and isn't a preallocated tunable that
	 * can be modified by kenv(2), microoptimise and treat it as a
	 * read-only string.
	 * A zero-length buffer indicates a fixed size read-only
	 * string.  In ddb, don't worry about trying to make a malloced
	 * snapshot.
	 */
	if ((oidp->oid_kind & (CTLFLAG_WR | CTLFLAG_TUN)) == 0 ||
	    arg2 == 0 || kdb_active) {
		arg2 = strlen((char *)arg1) + 1;
		ro_string = 1;
	}

	if (req->oldptr != NULL) {
		if (ro_string) {
			tmparg = arg1;
			outlen = strlen(tmparg) + 1;
		} else {
			tmparg = malloc(arg2, M_SYSCTLTMP, M_WAITOK);
			sx_slock(&sysctlstringlock);
			memcpy(tmparg, arg1, arg2);
			sx_sunlock(&sysctlstringlock);
			outlen = strlen(tmparg) + 1;
		}

		error = SYSCTL_OUT(req, tmparg, outlen);

		if (!ro_string)
			free(tmparg, M_SYSCTLTMP);
	} else {
		if (!ro_string)
			sx_slock(&sysctlstringlock);
		outlen = strlen((char *)arg1) + 1;
		if (!ro_string)
			sx_sunlock(&sysctlstringlock);
		error = SYSCTL_OUT(req, NULL, outlen);
	}
	if (error || !req->newptr)
		return (error);

	if (req->newlen - req->newidx >= arg2 ||
	    req->newlen - req->newidx < 0) {
		error = EINVAL;
	} else if (req->newlen - req->newidx == 0) {
		sx_xlock(&sysctlstringlock);
		((char *)arg1)[0] = '\0';
		sx_xunlock(&sysctlstringlock);
	} else {
		arg2 = req->newlen - req->newidx;
		tmparg = malloc(arg2, M_SYSCTLTMP, M_WAITOK);