什么是pstore

pstore最初是用于系統發生oops或panic時，自動保存內核log buffer中的日志。不過在當前內核版本中，其已經支持了更多的功能，如保存console日志、ftrace消息和用戶空間日志。同時，它還支持將這些消息保存在不同的存儲設備中，如內存、塊設備或mtd設備。 為了提高靈活性和可擴展性，pstore將以上功能分別抽象為前端和后端，其中像dmesg、console等為pstore提供數據的模塊稱為前端，而內存設備、塊設備等用于存儲數據的模塊稱為后端，pstore core則分別為它們提供相關的注冊接口。

通過模塊化的設計，實現了前端和后端的解耦，因此若某些模塊需要利用pstore保存信息，就可以方便地向pstore添加新的前端。而若需要將pstore數據保存到新的存儲設備上，也可以通過向其添加后端設備的方式完成。

除此之外，pstore還設計了一套pstore文件系統，用于查詢和操作上一次重啟時已經保存的pstore數據。當該文件系統被掛載時，保存在backend中的數據將被讀取到pstore fs中，并以文件的形式顯示。

pstore工作原理

pstore 源文件主要有以下幾個：fs/pstore/ram_core.c

fs/pstore/
├──ftrace.c#ftrace前端的實現
├──inode.c#pstore文件系統的注冊與操作
├──internal.h
├──Kconfig
├──Makefile
├──platform.c#pstore前后端功能的核心
├──pmsg.c#pmsg前端的實現
├──ram.c#pstore/ram后端的實現,dram空間分配與管理
├──ram_core.c#pstore/ram后端的實現,dram的讀寫操作

文件創建

pstore文件系統位置在：

#ls/sys/fs/pstore
console-ramoops-0dmesg-ramoops-0

控制臺日志位于 pstore 目錄下的console-ramoops文件中，因為采用console機制，該文件中的日志信息也受printk level控制，并不一定是全的。

oops/panic日志位于 pstore 目錄下的dmesg-ramoops-x文件中，根據緩沖區大小可以有多個文件，x從0開始。函數調用序列日志位于 pstore 目錄下的ftrace-ramoops文件中。

相關代碼在inode.c pstore_mkfile里：

/*
*Makearegularfileintherootdirectoryofourfilesystem.
*Loaditupwith"size"bytesofdatafrom"buf".
*Setthemtime&ctimetothedatethatthisrecordwasoriginallystored.
*/
intpstore_mkfile(enumpstore_type_idtype,char*psname,u64id,intcount,
char*data,boolcompressed,size_tsize,
structtimespectime,structpstore_info*psi)
{
........................

rc=-ENOMEM;
inode=pstore_get_inode(pstore_sb);
..............................

switch(type){
casePSTORE_TYPE_DMESG:
scnprintf(name,sizeof(name),"dmesg-%s-%lld%s",
psname,id,compressed?".enc.z":"");
break;
casePSTORE_TYPE_CONSOLE:
scnprintf(name,sizeof(name),"console-%s-%lld",psname,id);
break;
casePSTORE_TYPE_FTRACE:
scnprintf(name,sizeof(name),"ftrace-%s-%lld",psname,id);
break;
casePSTORE_TYPE_MCE:
scnprintf(name,sizeof(name),"mce-%s-%lld",psname,id);
break;
casePSTORE_TYPE_PPC_RTAS:
scnprintf(name,sizeof(name),"rtas-%s-%lld",psname,id);
break;
casePSTORE_TYPE_PPC_OF:
scnprintf(name,sizeof(name),"powerpc-ofw-%s-%lld",
psname,id);
break;
casePSTORE_TYPE_PPC_COMMON:
scnprintf(name,sizeof(name),"powerpc-common-%s-%lld",
psname,id);
break;
casePSTORE_TYPE_PMSG:
scnprintf(name,sizeof(name),"pmsg-%s-%lld",psname,id);
break;
casePSTORE_TYPE_PPC_OPAL:
sprintf(name,"powerpc-opal-%s-%lld",psname,id);
break;
casePSTORE_TYPE_UNKNOWN:
scnprintf(name,sizeof(name),"unknown-%s-%lld",psname,id);
break;
default:
scnprintf(name,sizeof(name),"type%d-%s-%lld",
type,psname,id);
break;
}
....................

dentry=d_alloc_name(root,name);
.......................

d_add(dentry,inode);
................
}

pstore_mkfile根據不同的type，使用snprintf函數生成文件名name。生成的文件名格式為--，其中type是enum pstore_type_id類型的一個值，psname是給定的psname參數，id是給定的id參數。

接著使用d_alloc_name函數為根目錄創建一個目錄項dentry，最后使用d_add函數將目錄項dentry與索引節點inode關聯起來，將其添加到文件系統中。

pstore_register

ramoops負責把message write到某個ram區域上，platform負責從ram讀取存到/sys/fs/pstore，ok，先來看機制代碼platform.c。

backend需要用pstore_register來注冊：

/*
*platformspecificpersistentstoragedriverregisterswith
*ushere.Ifpstoreisalreadymounted,calltheplatform
*readfunctionrightawaytopopulatethefilesystem.Ifnot
*thenthepstoremountcodewillcalluslatertofillout
*thefilesystem.
*/
intpstore_register(structpstore_info*psi)
{
structmodule*owner=psi->owner;

if(backend&&strcmp(backend,psi->name))
return-EPERM;

spin_lock(&pstore_lock);
if(psinfo){
spin_unlock(&pstore_lock);
return-EBUSY;
}

if(!psi->write)
psi->write=pstore_write_compat;
if(!psi->write_buf_user)
psi->write_buf_user=pstore_write_buf_user_compat;
psinfo=psi;
mutex_init(&psinfo->read_mutex);
spin_unlock(&pstore_lock);
...
/*
*Updatethemoduleparameterbackend,soitisvisible
*through/sys/module/pstore/parameters/backend
*/
backend=psi->name;

module_put(owner);

backend判斷確保一次只能有一個并記錄了全局psinfo。

看下結構體pstore_info:

structpstore_info{
structmodule*owner;
char*name;
spinlock_tbuf_lock;/*serializeaccessto'buf'*/
char*buf;
size_tbufsize;
structmutexread_mutex;/*serializeopen/read/close*/
intflags;
int(*open)(structpstore_info*psi);
int(*close)(structpstore_info*psi);
ssize_t(*read)(u64*id,enumpstore_type_id*type,
int*count,structtimespec*time,char**buf,
bool*compressed,ssize_t*ecc_notice_size,
structpstore_info*psi);
int(*write)(enumpstore_type_idtype,
enumkmsg_dump_reasonreason,u64*id,
unsignedintpart,intcount,boolcompressed,
size_tsize,structpstore_info*psi);
int(*write_buf)(enumpstore_type_idtype,
enumkmsg_dump_reasonreason,u64*id,
unsignedintpart,constchar*buf,boolcompressed,
size_tsize,structpstore_info*psi);
int(*write_buf_user)(enumpstore_type_idtype,
enumkmsg_dump_reasonreason,u64*id,
unsignedintpart,constchar__user*buf,
boolcompressed,size_tsize,structpstore_info*psi);
int(*erase)(enumpstore_type_idtype,u64id,
intcount,structtimespectime,
structpstore_info*psi);
void*data;
};

name就是backend的name了。

*write和*write_buf_user如果backend沒有給出會有個默認compat func，最終都走的*write_buf。

if(!psi->write)
psi->write=pstore_write_compat;
if(!psi->write_buf_user)
psi->write_buf_user=pstore_write_buf_user_compat;

staticintpstore_write_compat(enumpstore_type_idtype,
enumkmsg_dump_reasonreason,
u64*id,unsignedintpart,intcount,
boolcompressed,size_tsize,
structpstore_info*psi)
{
returnpsi->write_buf(type,reason,id,part,psinfo->buf,compressed,
size,psi);
}

staticintpstore_write_buf_user_compat(enumpstore_type_idtype,
enumkmsg_dump_reasonreason,
u64*id,unsignedintpart,
constchar__user*buf,
boolcompressed,size_tsize,
structpstore_info*psi)
{
...
ret=psi->write_buf(type,reason,id,part,psinfo->buf,
...
}

繼續pstore注冊：

if(pstore_is_mounted())
pstore_get_records(0);

如果pstore已經mounted，那就創建并填充文件by pstore_get_records:

/*
*Readalltherecordsfromthepersistentstore.Create
*filesinourfilesystem.Don'twarnabout-EEXISTerrors
*whenwearere-scanningthebackingstorelookingtoaddnew
*errorrecords.
*/
voidpstore_get_records(intquiet)
{
structpstore_info*psi=psinfo;//tj:globalpsinfo
...
mutex_lock(&psi->read_mutex);
if(psi->open&&psi->open(psi))
gotoout;

while((size=psi->read(&id,&type,&count,&time,&buf,&compressed,
&ecc_notice_size,psi))>0){
if(compressed&&(type==PSTORE_TYPE_DMESG)){
if(big_oops_buf)
unzipped_len=pstore_decompress(buf,
big_oops_buf,size,
big_oops_buf_sz);

if(unzipped_len>0){
if(ecc_notice_size)
memcpy(big_oops_buf+unzipped_len,
buf+size,ecc_notice_size);
kfree(buf);
buf=big_oops_buf;
size=unzipped_len;
compressed=false;
}else{
pr_err("decompressionfailed;returned%d
",
unzipped_len);
compressed=true;
}
}
rc=pstore_mkfile(type,psi->name,id,count,buf,
compressed,size+ecc_notice_size,
time,psi);
if(unzipped_lenclose)
psi->close(psi);
out:
mutex_unlock(&psi->read_mutex);

if needed，call pstore_decompress解壓然后創建pstore文件by vfs接口pstore_mkfile。

pstore注冊接下來是按類別分別注冊：

if(psi->flags&PSTORE_FLAGS_DMESG)
pstore_register_kmsg();
if(psi->flags&PSTORE_FLAGS_CONSOLE)
pstore_register_console();
if(psi->flags&PSTORE_FLAGS_FTRACE)
pstore_register_ftrace();
if(psi->flags&PSTORE_FLAGS_PMSG)
pstore_register_pmsg();

psi->flags仍是由backend決定，只看pstore_register_kmsg和pstore_register_console。

pstore panic log注冊

staticstructkmsg_dumperpstore_dumper={
.dump=pstore_dump,
};

/*
*Registerwithkmsg_dumptosavelastpartofconsolelogonpanic.
*/
staticvoidpstore_register_kmsg(void)
{
kmsg_dump_register(&pstore_dumper);
}

pstore_dump最終會call backend的write，直接用全局psinfo。

/*
*callbackfromkmsg_dump.(s2,l2)hasthemostrecently
*writtenbytes,olderbytesarein(s1,l1).Saveasmuch
*aswecanfromtheendofthebuffer.
*/
staticvoidpstore_dump(structkmsg_dumper*dumper,
enumkmsg_dump_reasonreason)
{
...
ret=psinfo->write(PSTORE_TYPE_DMESG,reason,&id,part,
oopscount,compressed,total_len,psinfo);

kmsg_dump_register是內核一種增加log dumper方法，called when kernel oopses or panic。

/**
*kmsg_dump_register-registerakernellogdumper.
*@dumper:pointertothekmsg_dumperstructure
*
*Addsakernellogdumpertothesystem.Thedumpcallbackinthe
*structurewillbecalledwhenthekerneloopsesorpanicsandmustbe
*set.Returnszeroonsuccessand%-EINVALor%-EBUSYotherwise.
*/
intkmsg_dump_register(structkmsg_dumper*dumper)
{
unsignedlongflags;
interr=-EBUSY;

/*Thedumpcallbackneedstobeset*/
if(!dumper->dump)
return-EINVAL;

spin_lock_irqsave(&dump_list_lock,flags);
/*Don'tallowregisteringmultipletimes*/
if(!dumper->registered){
dumper->registered=1;
list_add_tail_rcu(&dumper->list,&dump_list);
err=0;
}
spin_unlock_irqrestore(&dump_list_lock,flags);

returnerr;
}

/**
*kmsg_dump-dumpkernellogtokernelmessagedumpers.
*@reason:thereason(oops,panicetc)fordumping
*
*Calleachoftheregistereddumper'sdump()callback,whichcan
*retrievethekmsgrecordswithkmsg_dump_get_line()or
*kmsg_dump_get_buffer().
*/
voidkmsg_dump(enumkmsg_dump_reasonreason)
{
structkmsg_dumper*dumper;
unsignedlongflags;

if((reason>KMSG_DUMP_OOPS)&&!always_kmsg_dump)
return;

rcu_read_lock();
list_for_each_entry_rcu(dumper,&dump_list,list){
if(dumper->max_reason&&reason>dumper->max_reason)
continue;

/*initializeiteratorwithdataaboutthestoredrecords*/
dumper->active=true;

raw_spin_lock_irqsave(&logbuf_lock,flags);
dumper->cur_seq=clear_seq;
dumper->cur_idx=clear_idx;
dumper->next_seq=log_next_seq;
dumper->next_idx=log_next_idx;
raw_spin_unlock_irqrestore(&logbuf_lock,flags);

/*invokedumperwhichwilliterateoverrecords*/
dumper->dump(dumper,reason);

/*resetiterator*/
dumper->active=false;
}
rcu_read_unlock();
}

pstore console 注冊

staticstructconsolepstore_console={
.name="pstore",
.write=pstore_console_write,
.flags=CON_PRINTBUFFER|CON_ENABLED|CON_ANYTIME,
.index=-1,
};

staticvoidpstore_register_console(void)
{
register_console(&pstore_console);
}

->write最終也會call backend write:

#ifdefCONFIG_PSTORE_CONSOLE
staticvoidpstore_console_write(structconsole*con,constchar*s,unsignedc)
{
constchar*e=s+c;

while(spsinfo->bufsize)
c=psinfo->bufsize;

if(oops_in_progress){
if(!spin_trylock_irqsave(&psinfo->buf_lock,flags))
break;
}else{
spin_lock_irqsave(&psinfo->buf_lock,flags);
}
memcpy(psinfo->buf,s,c);
psinfo->write(PSTORE_TYPE_CONSOLE,0,&id,0,0,0,c,psinfo);//tj:here
spin_unlock_irqrestore(&psinfo->buf_lock,flags);
s+=c;
c=e-s;
}
}

ramoops

下面來看下RAM backend: ramoops，先看probe:

staticintramoops_probe(structplatform_device*pdev)
{
structdevice*dev=&pdev->dev;
structramoops_platform_data*pdata=dev->platform_data;
...

if(!pdata->mem_size||(!pdata->record_size&&!pdata->console_size&&
!pdata->ftrace_size&&!pdata->pmsg_size)){
pr_err("Thememorysizeandtherecord/consolesizemustbe"
"non-zero
");
gotofail_out;
}
...

cxt->size=pdata->mem_size;
cxt->phys_addr=pdata->mem_address;
cxt->memtype=pdata->mem_type;
cxt->record_size=pdata->record_size;
cxt->console_size=pdata->console_size;
cxt->ftrace_size=pdata->ftrace_size;
cxt->pmsg_size=pdata->pmsg_size;
cxt->dump_oops=pdata->dump_oops;
cxt->ecc_info=pdata->ecc_info;

pdata應該來源ramoops_register_dummy:

staticvoidramoops_register_dummy(void)
{
...
pr_info("usingmoduleparameters
");

dummy_data=kzalloc(sizeof(*dummy_data),GFP_KERNEL);
if(!dummy_data){
pr_info("couldnotallocatepdata
");
return;
}

dummy_data->mem_size=mem_size;
dummy_data->mem_address=mem_address;
dummy_data->mem_type=mem_type;
dummy_data->record_size=record_size;
dummy_data->console_size=ramoops_console_size;
dummy_data->ftrace_size=ramoops_ftrace_size;
dummy_data->pmsg_size=ramoops_pmsg_size;
dummy_data->dump_oops=dump_oops;
/*
*Forbackwardscompatibilityramoops.ecc=1means16bytesECC
*(using1byteforECCisn'tmuchofuseanyway).
*/
dummy_data->ecc_info.ecc_size=ramoops_ecc==1?16:ramoops_ecc;

dummy=platform_device_register_data(NULL,"ramoops",-1,
dummy_data,sizeof(structramoops_platform_data));

有幾個可配參數:

/*
*Ramoopsplatformdata
*@mem_sizememorysizeforramoops
*@mem_addressphysicalmemoryaddresstocontainramoops
*/

structramoops_platform_data{
unsignedlongmem_size;
phys_addr_tmem_address;
unsignedintmem_type;
unsignedlongrecord_size;
unsignedlongconsole_size;
unsignedlongftrace_size;
unsignedlongpmsg_size;
intdump_oops;
structpersistent_ram_ecc_infoecc_info;
};

mem_size：用于Ramoops的內存大小，表示分配給Ramoops的物理內存的大小。

mem_address：用于Ramoops的物理內存地址，指定用于存儲Ramoops的物理內存的起始地址。

mem_type：內存類型，用于進一步描述內存的屬性和特征。

record_size：每個記錄的大小

console_size：控制臺記錄的大小

ftrace_size：Ftrace記錄的大小

pmsg_size：pmsg消息記錄的大小

dump_oops：是否轉儲oops信息的標志，表示是否將oops信息轉儲到Ramoops中。

ecc_info：RAM的ECC（糾錯碼）信息，用于提供關于ECC配置和處理的詳細信息。

有個結構表示了ramoops的context:

structramoops_context{
structpersistent_ram_zone**przs;
structpersistent_ram_zone*cprz;
structpersistent_ram_zone*fprz;
structpersistent_ram_zone*mprz;
phys_addr_tphys_addr;
unsignedlongsize;
unsignedintmemtype;
size_trecord_size;
size_tconsole_size;
size_tftrace_size;
size_tpmsg_size;
intdump_oops;
structpersistent_ram_ecc_infoecc_info;
unsignedintmax_dump_cnt;
unsignedintdump_write_cnt;
/*_read_cntneedclearonramoops_pstore_open*/
unsignedintdump_read_cnt;
unsignedintconsole_read_cnt;
unsignedintftrace_read_cnt;
unsignedintpmsg_read_cnt;
structpstore_infopstore;
};

在ramoops_probe時也是把ramoops_platform_data的成員賦給了context對應的。要了解具體含義，繼續probe:

paddr=cxt->phys_addr;

dump_mem_sz=cxt->size-cxt->console_size-cxt->ftrace_size
-cxt->pmsg_size;
err=ramoops_init_przs(dev,cxt,&paddr,dump_mem_sz);
if(err)
gotofail_out;

err=ramoops_init_prz(dev,cxt,&cxt->cprz,&paddr,
cxt->console_size,0);
if(err)
gotofail_init_cprz;

err=ramoops_init_prz(dev,cxt,&cxt->fprz,&paddr,cxt->ftrace_size,
LINUX_VERSION_CODE);
if(err)
gotofail_init_fprz;

err=ramoops_init_prz(dev,cxt,&cxt->mprz,&paddr,cxt->pmsg_size,0);
if(err)
gotofail_init_mprz;

cxt->pstore.data=cxt;

可見，是逐個init每個persistant ram zone，size一共有4段：

dump_mem_sz+cxt->console_size+cxt->ftrace_size+cxt->pmsg_size=cxt->size

mem_size就是總大小了，mem_address是ramoops的物理地址，record_size再看下oops/panic ram：

staticintramoops_init_przs(structdevice*dev,structramoops_context*cxt,
phys_addr_t*paddr,size_tdump_mem_sz)
{
interr=-ENOMEM;
inti;

if(!cxt->record_size)
return0;

if(*paddr+dump_mem_sz-cxt->phys_addr>cxt->size){
dev_err(dev,"noroomfordumps
");
return-ENOMEM;
}

cxt->max_dump_cnt=dump_mem_sz/cxt->record_size;
if(!cxt->max_dump_cnt)
return-ENOMEM;

ok dump_mem_size大小的區域分成max_dump_cnt個，每個記錄大小是record_size。

接著會call persistent_ram_new來分配內存給這個ram zone。

for(i=0;imax_dump_cnt;i++){
cxt->przs[i]=persistent_ram_new(*paddr,cxt->record_size,0,
&cxt->ecc_info,
cxt->memtype,0);

console/ftrace/pmsg ram zone同上分配。

最后處理flags并注冊pstore:

cxt->pstore.flags=PSTORE_FLAGS_DMESG;//tj:默認dumpoops/panic
if(cxt->console_size)
cxt->pstore.flags|=PSTORE_FLAGS_CONSOLE;
if(cxt->ftrace_size)
cxt->pstore.flags|=PSTORE_FLAGS_FTRACE;
if(cxt->pmsg_size)
cxt->pstore.flags|=PSTORE_FLAGS_PMSG;

err=pstore_register(&cxt->pstore);
if(err){
pr_err("registeringwithpstorefailed
");
gotofail_buf;
}

來看下ramoops pstore的定義的callback，他們通過全局psinfo而來：

staticstructramoops_contextoops_cxt={
.pstore={
.owner=THIS_MODULE,
.name="ramoops",
.open=ramoops_pstore_open,
.read=ramoops_pstore_read,//psi->read
.write_buf=ramoops_pstore_write_buf,//fornonpmsg
.write_buf_user=ramoops_pstore_write_buf_user,//forpmsg
.erase=ramoops_pstore_erase,
},
};

pstore使用方法

ramoops

配置內核

CONFIG_PSTORE=y
CONFIG_PSTORE_CONSOLE=y
CONFIG_PSTORE_PMSG=y
CONFIG_PSTORE_RAM=y
CONFIG_PANIC_TIMEOUT=-1

由于log數據存放于DDR，不能掉電，只能依靠自動重啟機制來查看，故而要配置：CONFIG_PANIC_TIMEOUT，讓系統在 panic 后能自動重啟。

dts

ramoops_mem:ramoops_mem{
reg=<0x0?0x110000?0x0?0xf0000>;
reg-names="ramoops_mem";
};

ramoops{
compatible="ramoops";
record-size=<0x0?0x20000>;
console-size=<0x0?0x80000>;
ftrace-size=<0x0?0x00000>;
pmsg-size=<0x0?0x50000>;
memory-region=<&ramoops_mem>;
};

mtdoops

內核配置

CONFIG_PSTORE=y
CONFIG_PSTORE_CONSOLE=y
CONFIG_PSTORE_PMSG=y
CONFIG_MTD_OOPS=y
CONFIG_MAGIC_SYSRQ=y

分區配置

cmdline方式：

bootargs="console=ttyS1,115200loglevel=8rootwaitroot=/dev/mtdblock5rootfstype=squashfsmtdoops.mtddev=pstore";

blkparts="mtdparts=spi0.0:64k(spl)ro,256k(uboot)ro,64k(dtb)ro,128k(pstore),3m(kernel)ro,4m(rootfs)ro,-(data)";

part of方式：

bootargs="console=ttyS1,115200loglevel=8rootwaitroot=/dev/mtdblock5rootfstype=squashfsmtdoops.mtddev=pstore";

partition@60000{
label="pstore";
reg=<0x60000?0x20000>;
};

blkoops

配置內核

CONFIG_PSTORE=y
CONFIG_PSTORE_CONSOLE=y
CONFIG_PSTORE_PMSG=y
CONFIG_PSTORE_BLK=y
CONFIG_MTD_PSTORE=y
CONFIG_MAGIC_SYSRQ=y

配置分區

cmdline方式：

bootargs="console=ttyS1,115200loglevel=8rootwaitroot=/dev/mtdblock5rootfstype=squashfspstore_blk.blkdev=pstore";

blkparts="mtdparts=spi0.0:64k(spl)ro,256k(uboot)ro,64k(dtb)ro,128k(pstore),3m(kernel)ro,4m(rootfs)ro,-(data)";

part of方式：

bootargs="console=ttyS1,115200loglevel=8rootwaitroot=/dev/mtdblock5rootfstype=squashfspstore_blk.blkdev=pstore";

partition@60000{
label="pstore";
reg=<0x60000?0x20000>;
};

pstore fs

掛載pstore文件系統

mount-tpstorepstore/sys/fs/pstore

掛載后，通過mount能看到類似這樣的信息：

#mount
pstoreon/sys/fs/pstoretypepstore(rw,relatime)

如果需要驗證，可以這樣主動觸發內核崩潰：

#echoc>/proc/sysrq-trigger

不同配置方式日志名稱不同

ramoops

#mount-tpstorepstore/sys/fs/pstore/
#cd/sys/fs/pstore/
#ls
console-ramoops-0dmesg-ramoops-0dmesg-ramoops-1

mtdoops

#cat/dev/mtd3>1.txt
#cat1.txt

blkoops

cd/sys/fs/pstore/
ls
dmesg-pstore_blk-0dmesg-pstore_blk-1

總結

pstore setup 流程：

ramoops_init
ramoops_register_dummy
ramoops_probe
ramoops_register

查看 pstore 數據保存流程：

registerapstore_dumper
//whenpanichappens,kmsg_dumpiscalled
calldumper->dump
pstore_dump

查看 pstore 數據讀取流程：

ramoops_probe
persistent_ram_post_init
pstore_register
pstore_get_records
ramoops_pstore_read
pstore_decompress(onlyfordmesg)
pstore_mkfile(savetofiles)