47 lines
1.4 KiB
Markdown
47 lines
1.4 KiB
Markdown
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---
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title: Kernel, creation of new process
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date: 2023-11-26T07:44:51.449Z
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slug: kernel-new-process-creation
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description: "Deep dive Linux Kernel #3"
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---
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```c
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static int init(void * unused)
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{
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lock_kernel();
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do_basic_setup();
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/*
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* Ok, we have completed the initial bootup, and
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* we're essentially up and running. Get rid of the
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* initmem segments and start the user-mode stuff..
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*/
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free_initmem();
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unlock_kernel();
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if (open("/dev/console", O_RDWR, 0) < 0)
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printk("Warning: unable to open an initial console.\n");
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(void) dup(0);
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(void) dup(0);
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/*
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* We try each of these until one succeeds.
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*
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* The Bourne shell can be used instead of init if we are
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* trying to recover a really broken machine.
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*/
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if (execute_command)
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execve(execute_command,argv_init,envp_init);
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execve("/sbin/init",argv_init,envp_init);
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execve("/etc/init",argv_init,envp_init);
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execve("/bin/init",argv_init,envp_init);
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execve("/bin/sh",argv_init,envp_init);
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panic("No init found. Try passing init= option to kernel.");
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}
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```
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At `open("/dev/console") is opens fd 0, and with two `dup(0)`, fd 0, 1, 2 as stdin, stdout, stderr opens. When `execve()` or `fork()` happens, it simply copies calling process's `task_struct` as process context, so all file descriptors are also passed down.
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All processes' file descriptor 0, 1, 2 are all originates to `init`'s file descriptor, set up like above.
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