linux中0号进程的含义是什么

/*
*Setupthefirsttasktable,touchatyourownrisk!.Base=0,
*limit=0x1fffff(=2MB)
*/
structtask_structinit_task
={
#ifdefCONFIG_THREAD_INFO_IN_TASK
.thread_info=INIT_THREAD_INFO(init_task),
.stack_refcount=ATOMIC_INIT(1),
#endif
.state=0,
.stack=init_stack,
.usage=ATOMIC_INIT(2),
.flags=PF_KTHREAD,
.prio=MAX_PRIO-20,
.static_prio=MAX_PRIO-20,
.normal_prio=MAX_PRIO-20,
.policy=SCHED_NORMAL,
.cpus_allowed=CPU_MASK_ALL,
.nr_cpus_allowed=NR_CPUS,
.mm=NULL,
.active_mm=&init_mm,
.tasks=LIST_HEAD_INIT(init_task.tasks),
.ptraced=LIST_HEAD_INIT(init_task.ptraced),
.ptrace_entry=LIST_HEAD_INIT(init_task.ptrace_entry),
.real_parent=&init_task,
.parent=&init_task,
.children=LIST_HEAD_INIT(init_task.children),
.sibling=LIST_HEAD_INIT(init_task.sibling),
.group_leader=&init_task,
RCU_POINTER_INITIALIZER(real_cred,&init_cred),
RCU_POINTER_INITIALIZER(cred,&init_cred),
.comm=INIT_TASK_COMM,
.thread=INIT_THREAD,
.fs=&init_fs,
.files=&init_files,
.signal=&init_signals,
.sighand=&init_sighand,
.blocked={{0}},
.alloc_lock=__SPIN_LOCK_UNLOCKED(init_task.alloc_lock),
.journal_info=NULL,
INIT_CPU_TIMERS(init_task)
.pi_lock=__RAW_SPIN_LOCK_UNLOCKED(init_task.pi_lock),
.timer_slack_ns=50000,/*50usecdefaultslack*/
.thread_pid=&init_struct_pid,
.thread_group=LIST_HEAD_INIT(init_task.thread_group),
.thread_node=LIST_HEAD_INIT(init_signals.thread_head),
};
EXPORT_SYMBOL(init_task);

#defineINIT_TASK_DATA(align)
.=ALIGN(align);
__start_init_task=.;
init_thread_union=.;
init_stack=.;
KEEP(*(.data..init_task))
KEEP(*(.data..init_thread_info))
.=__start_init_task+THREAD_SIZE;
__end_init_task=.;

/*
*Kernelstartupentrypoint.
*---------------------------
*
*Therequirementsare:
*MMU=off,D-cache=off,I-cache=onoroff,
*x0=physicaladdresstotheFDTblob.
*
*Thiscodeismostlypositionindependentsoyoucallthisat
*__pa(PAGE_OFFSET+TEXT_OFFSET).
*
*Notethatthecallee-savedregistersareusedforstoringvariables
*thatareusefulbeforetheMMUisenabled.Theallocationsaredescribed
*intheentryroutines.
*/
/*
*Thefollowingcalleesavedgeneralpurposeregistersareusedonthe
*primarylowlevelbootpath:
*
*RegisterScopePurpose
*x21stext()..start_kernel()FDTpointerpassedatbootinx0
*x23stext()..start_kernel()physicalmisalignment/KASLRoffset
*x28__create_page_tables()calleepreservedtempregister
*x19/x20__primary_switch()calleepreservedtempregisters
*/
ENTRY(stext)
blpreserve_boot_args
blel2_setup//DroptoEL1,w0=cpu_boot_mode
adrpx23,__PHYS_OFFSET
andx23,x23,MIN_KIMG_ALIGN-1//KASLRoffset,defaultsto0
blset_cpu_boot_mode_flag
bl__create_page_tables
/*
*ThefollowingcallsCPUsetupcode,seearch/arm64/mm/proc.Sfor
*details.
*Onreturn,theCPUwillbereadyfortheMMUtobeturnedonand
*theTCRwillhavebeenset.
*/
bl__cpu_setup//initialiseprocessor
b__primary_switch
ENDPROC(stext)

/*
*ThefollowingfragmentofcodeisexecutedwiththeMMUenabled.
*
*x0=__PHYS_OFFSET
*/
__primary_switched:
adrpx4,init_thread_union
addsp,x4,#THREAD_SIZE
adr_lx5,init_task
msrsp_el0,x5//Savethread_info

adr_lx8,vectors//loadVBAR_EL1withvirtual
msrvbar_el1,x8//vectortableaddress
isb

stpxzr,x30,[sp,#-16]!
movx29,sp

str_lx21,__fdt_pointer,x5//SaveFDTpointer

ldr_lx4,kimage_vaddr//Savetheoffsetbetween
subx4,x4,x0//thekernelvirtualand
str_lx4,kimage_voffset,x5//physicalmappings

//ClearBSS
adr_lx0,__bss_start
movx1,xzr
adr_lx2,__bss_stop
subx2,x2,x0
bl__pi_memset
dsbishst//MakezeropagevisibletoPTW

addsp,sp,#16
movx29,#0
movx30,#0
bstart_kernel
ENDPROC(__primary_switched)

asmlinkage__visiblevoid__initstart_kernel(void)
{
char*command_line;
char*after_dashes;
set_task_stack_end_magic(&init_task);
smp_setup_processor_id();
debug_objects_early_init();
cgroup_init_early();
local_irq_disable();
early_boot_irqs_disabled=true;
/*
*Interruptsarestilldisabled.Donecessarysetups,then
*enablethem.
*/
boot_cpu_init();
page_address_init();
pr_notice("%s",linux_banner);
setup_arch(&command_line);
/*
*Setupthetheinitialcanaryandentropyafterarch
*andafteraddinglatentandcommandlineentropy.
*/
add_latent_entropy();
add_device_randomness(command_line,strlen(command_line));
boot_init_stack_canary();
mm_init_cpumask(&init_mm);
setup_command_line(command_line);
setup_nr_cpu_ids();
setup_per_cpu_areas();
smp_prepare_boot_cpu();/*arch-specificboot-cpuhooks*/
boot_cpu_hotplug_init();
build_all_zonelists(NULL);
page_alloc_init();
。。。。。。。
acpi_subsystem_init();
arch_post_acpi_subsys_init();
sfi_init_late();
/*Dotherestnon-__init'ed,we'renowalive*/
arch_call_rest_init();
}
void__init__weakarch_call_rest_init(void)
{
rest_init();
}

noinlinevoid__refrest_init(void)
{
structtask_struct*tsk;
intpid;
rcu_scheduler_starting();
/*
*Weneedtospawninitfirstsothatitobtainspid1,however
*theinittaskwillendupwantingtocreatekthreads,which,if
*wescheduleitbeforewecreatekthreadd,willOOPS.
*/
pid=kernel_thread(kernel_init,NULL,CLONE_FS);
/*
*PininitonthebootCPU.Taskmigrationisnotproperlyworking
*untilsched_init_smp()hasbeenrun.Itwillsettheallowed
*CPUsforinittothenonisolatedCPUs.
*/
rcu_read_lock();
tsk=find_task_by_pid_ns(pid,&init_pid_ns);
set_cpus_allowed_ptr(tsk,cpumask_of(smp_processor_id()));
rcu_read_unlock();
numa_default_policy();
pid=kernel_thread(kthreadd,NULL,CLONE_FS|CLONE_FILES);
rcu_read_lock();
kthreadd_task=find_task_by_pid_ns(pid,&init_pid_ns);
rcu_read_unlock();
/*
*Enablemight_sleep()andsmp_processor_id()checks.
*TheycannotbeenabledearlierbecausewithCONFIG_PREEMPT=y
*kernel_thread()wouldtriggermight_sleep()splats.With
*CONFIG_PREEMPT_VOLUNTARY=ytheinittaskmighthavescheduled
*already,butit'sstuckonthekthreadd_donecompletion.
*/
system_state=SYSTEM_SCHEDULING;
complete(&kthreadd_done);
}

staticint__refkernel_init(void*unused)
{
intret;
kernel_init_freeable();
/*needtofinishallasync__initcodebeforefreeingthememory*/
async_synchronize_full();
ftrace_free_init_mem();
free_initmem();
mark_readonly();
/*
*Kernelmappingsarenowfinalized-updatetheuserspacepage-table
*tofinalizePTI.
*/
pti_finalize();
system_state=SYSTEM_RUNNING;
numa_default_policy();
rcu_end_inkernel_boot();
if(ramdisk_execute_command){
ret=run_init_process(ramdisk_execute_command);
if(!ret)
return0;
pr_err("Failedtoexecute%s(error%d)n",
ramdisk_execute_command,ret);
}
/*
*Wetryeachoftheseuntilonesucceeds.
*
*TheBourneshellcanbeusedinsteadofinitifweare
*tryingtorecoverareallybrokenmachine.
*/
if(execute_command){
ret=run_init_process(execute_command);
if(!ret)
return0;
panic("Requestedinit%sfailed(error%d).",
execute_command,ret);
}
if(!try_to_run_init_process("/sbin/init")||
!try_to_run_init_process("/etc/init")||
!try_to_run_init_process("/bin/init")||
!try_to_run_init_process("/bin/sh"))
return0;
panic("Noworkinginitfound.Trypassinginit=optiontokernel."
"SeeLinuxDocumentation/admin-guide/init.rstforguidance.");
}