Fork

Fork

[Christophe DUMONT]

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Hello,

How does the kernel knows when a process calls the fork function that he has the rights to create a new process ?



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Re: Fork

[Valentin Vidić]

On Thu, Jan 09, 2020 at 10:35:16AM +0000, Christophe DUMONT wrote:
> How does the kernel knows when a process calls the fork function that
> he has the rights to create a new process ?

Not sure what you mean by rights, but in copy_process you can
see different checks and errors that can happen when creating
a new process:

https://elixir.bootlin.com/linux/latest/source/kernel/fork.c#L1760

-- 
Valentin

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fork

[Nitin Varyani]

Linux kernel development by Robert Love describes the fork process as

fork() -> clone() -> do_fork() -> copy_process()

I am unable to find the clone() system call in linux 3.13.
Can someone explain the proper flow of fork() system call initiated by the
user?

Where can I find the libc implementation for fork()? I want the code of all
the functions involved in fork.
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fork

[Alex Wilson]

On Mon, Apr 18, 2016 at 12:48 AM, Nitin Varyani
<varyani.nitin1@gmail.com> wrote:
>
>
> Linux kernel development by Robert Love describes the fork process as
>
> fork() -> clone() -> do_fork() -> copy_process()
>
> I am unable to find the clone() system call in linux 3.13.
> Can someone explain the proper flow of fork() system call initiated by the user?
>
> Where can I find the libc implementation for fork()? I want the code of all the functions involved in fork.
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>

I believe the fork and clone syscalls are found at /kernel/fork.c
under 3.13. (see link below)
They're wrapped in the nice SYSCALL_DEFINE# macros and all seem to
call do_fork().

http://lxr.free-electrons.com/source/kernel/fork.c?v=3.13#L1641

Can't really help you on the libc part, and you would need to specify
which libc implementation you're interested in.

fork

[Cihangir Akturk]

On Mon, Apr 18, 2016 at 12:18:00PM +0530, Nitin Varyani wrote:
> Linux kernel development by Robert Love describes the fork process as
> 
> fork() -> clone() -> do_fork() -> copy_process()
> 
> I am unable to find the clone() system call in linux 3.13.
> Can someone explain the proper flow of fork() system call initiated by the
> user?
> 
> Where can I find the libc implementation for fork()? I want the code of all
> the functions involved in fork.

There are a couple of libc implemetations out there, say musl,
dietlibc, uClibc and so on. But If you mean GNU libc aka. glibc
then this is what you are looking for:

https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/nptl/fork.c;h=1a68cbd6476b3268b5b7ac09ae60c35ce7069219;hb=HEAD#l47

__libc_fork() calls clone() syscall internally using a bit of
assembler magic.