03628c8f7
Rob Landley
2006-01-29
Subject
Remind me to implement bb_fork_exec()...
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docs/busybox.net/programming.html+11 -0
| @@ -235,6 +235,12 @@ second argument to pw_encrypt(text,buffer).</p> | |
| <h2><a name="tips_vfork">Fork and vfork</a></h2> | |
| + | <p>Busybox hides the difference between fork() and vfork() in |
| + | libbb/bb_fork_exec.c. If you ever want to fork and exec, use bb_fork_exec() |
| + | (which returns a pid and takes the same arguments as execve(), although in |
| + | this case envp can be NULL) and don't worry about it. This description is |
| + | here in case you want to know why that does what it does.</p> |
| + | |
| <p>On systems that haven't got a Memory Management Unit, fork() is unreasonably | |
| expensive to implement, so a less capable function called vfork() is used | |
| instead.</p> | |
| @@ -277,6 +283,11 @@ processes running at the same time. It means you can't have two processes | |
| sharing the same memory without stomping all over each other. As soon as | |
| the child calls exec(), the parent resumes.</p> | |
| + | <p>If the child's attempt to call exec() fails, the child should call _exit() |
| + | rather than a normal exit(). This avoids any atexit() code that might confuse |
| + | the parent. (The parent should never call _exit(), only a vforked child that |
| + | failed to exec.)</p> |
| + | |
| <p>(Now in theory, a nommu system could just copy the _stack_ when it forks | |
| (which presumably is much shorter than the heap), and leave the heap shared. | |
| In practice, you've just wound up in a multi-threaded situation and you can't | |