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.Dd April 26, 2018 .Dt CPU_LWP_FORK 9 .Os .Sh NAME .Nm cpu_lwp_fork , .Nm child_return , .Nm lwp_trampoline .Nd finish a fork operation .Sh SYNOPSIS n sys/proc.h .Ft void .Fn cpu_lwp_fork "struct lwp *l1" "struct lwp *l2" "void *stack" \ "size_t stacksize" "void (*func)(void *)" "void *arg" .Ft void .Fn child_return "void *arg" .Sh DESCRIPTION .Fn cpu_lwp_fork is the machine-dependent portion of .Fn fork1 which finishes a fork operation, with child lwp .Fa l2 nearly set up. It copies and updates the PCB and trap frame from the parent .Fa l1 , making the child ready to run.
p .Fn cpu_lwp_fork rigs the child's kernel stack so that it will start in .Fn lwp_trampoline . .Fn lwp_trampoline does not have a normal calling sequence and is entered by .Fn cpu_switchto . If an alternate user-level stack is requested (with non-zero values in both the .Fa stack and .Fa stacksize arguments), the user stack pointer is set up accordingly.
p After being entered by .Fn cpu_switchto and while running in user context (within the kernel) .Fn lwp_trampoline will invoke the function .Fa func with the argument .Fa arg . If a kernel thread is being created, the return path and argument are specified with .Fa func and .Fa arg . If a user process is being created, .Fn fork1 will pass .Fn child_return and .Fa l2 to .Fn cpu_lwp_fork as .Fa func and .Fa arg respectively. This causes the newly-created child process to go directly to user level with an apparent return value of 0 from .Xr fork 2 , while the parent process returns normally. .Sh SEE ALSO .Xr fork 2 , .Xr cpu_switchto 9 , .Xr fork1 9