[lvm-devel] Question about destroy_toolcontext()

[Zdenek Kabelac]

Dne 17.8.2016 v 11:04 Liuhua Wang napsal(a):
> Hi Peter,
>
> I read the source of lib/commands/toolcontext.c
> and have a question about the following lines:
>
> ----------------------------
> void destroy_toolcontext(struct cmd_context *cmd){
>
> [snip]
>
>   #ifndef VALGRIND_POOL
>     if (cmd->linebuffer) {
>         /* Reset stream buffering to defaults */
>         if (is_valid_fd(STDIN_FILENO) &&
>             ((flags = fcntl(STDIN_FILENO, F_GETFL)) > 0) &&
>             (flags & O_ACCMODE) != O_WRONLY) {
>             if (_reopen_stream(stdin, STDIN_FILENO, "r", "stdin", &new_stream)) {
>                 stdin = new_stream;
>                 setlinebuf(stdin);
>             } else
>                 cmd->linebuffer = NULL; /* Leave buffer in place (deliberate leak) */
>         }
>
>         if (is_valid_fd(STDOUT_FILENO) &&
>             ((flags = fcntl(STDOUT_FILENO, F_GETFL)) > 0) &&
>             (flags & O_ACCMODE) != O_RDONLY) {
>             if (_reopen_stream(stdout, STDOUT_FILENO, "w", "stdout", &new_stream)) {
>                 stdout = new_stream;
>                 setlinebuf(stdout);
>             } else
>                 cmd->linebuffer = NULL; /* Leave buffer in place (deliberate leak) */
>         }
>
>         dm_free(cmd->linebuffer);
>     }
>   #endif
> -------------------------------
> when cmd->linebuffer is NULL and then dm_free(cmd->linebuffer),
> won't it make it segfault?


dm_free()  accepts  NULL   (just like 'free()' - for details see:  man 3 free.

Regards

Zdenek