RE: [PATCH 1/1] tracing: Support reading trace event format file larger than PAGE_SIZE

Shiju Jose
2025-01-07T11:05:01Z

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>-----Original Message-----
>From: Steven Rostedt <rostedt@goodmis.org>
>Sent: 06 January 2025 22:12
>To: Shiju Jose <shiju.jose@huawei.com>
>Cc: mhiramat@kernel.org; mathieu.desnoyers@efficios.com; linux-trace-
>kernel@vger.kernel.org; linux-kernel@vger.kernel.org; Linuxarm
><linuxarm@huawei.com>; Jonathan Cameron
><jonathan.cameron@huawei.com>; tanxiaofei <tanxiaofei@huawei.com>;
>Zengtao (B) <prime.zeng@hisilicon.com>
>Subject: Re: [PATCH 1/1] tracing: Support reading trace event format file larger
>than PAGE_SIZE
>
>On Mon, 6 Jan 2025 18:15:36 +0000
>Shiju Jose <shiju.jose@huawei.com> wrote:
>
>> >You see, it requires multiple reads to pull in an entire kernel
>> >pseudo file. None of those reads are greater than PAGE_SIZE. Why
>> >should trace format files be any different?
>> Thanks for the reply.
>> Yes. I had a fix/workaround in the userspace rasdaemon with multiple
>> reads like above as reported previously in the following thread.
>> https://lore.kernel.org/lkml/3c9808a694d242cab35bab67602edebf@huawei.c
>> om/ However thought a solution in the common kernel code for the
>> format file may be better. I will go ahead with the user space
>> solution.
>
>That would make it different than every other pseudo file in the kernel. I rather
>not do that.
>
>>
>> Also shared an information in the above thread about libtraceevent
>> __parse_event() does not return error when parse_format() fail with
>> incomplete formt data, which resulted initialization for the trace event does
>not fail in the user space tool.
>
>Hmm, can you send me the the format file that failed?
>
>Just the output of "cat /sys/kernel/tracing/events/<system>/<event>/format"
>will do.

Please find attached format file, which might have failed to parse because of the
unsupported formats in the libtraceevent you mentioned in the following thread.
https://lore.kernel.org/lkml/20241127104132.6c1729e1@gandalf.local.home/#t

Please find the improvement in the libraceevent which I mentioned for not returning error
when parsing failed,
===========================================
diff --git a/src/event-parse.c b/src/event-parse.c index 0427061..b9264cb 100644
--- a/src/event-parse.c
+++ b/src/event-parse.c
@@ -7905,9 +7905,14 @@ __parse_event(struct tep_handle *tep,
const char *buf, unsigned long size,
const char *sys)
{
- int ret = parse_format(eventp, tep, buf, size, sys);
- struct tep_event *event = *eventp;
+ int ret;
+ struct tep_event *event;
+
+ ret = parse_format(eventp, tep, buf, size, sys);
+ if (ret)
+ return ret;

+ event = *eventp;
if (event == NULL)
return ret;
=========================================
>
>-- Steve

Thanks,
Shiju

[-- Attachment #2: format_cxl_general_media --]
[-- Type: application/octet-stream, Size: 5089 bytes --]

name: cxl_general_media
ID: 1497
format:
field:unsigned short common_type; offset:0; size:2; signed:0;
field:unsigned char common_flags; offset:2; size:1; signed:0;
field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
field:int common_pid; offset:4; size:4; signed:1;

field:__data_loc char[] memdev; offset:8; size:4; signed:0;
field:__data_loc char[] host; offset:12; size:4; signed:0;
field:int log; offset:16; size:4; signed:1;
field:uuid_t hdr_uuid; offset:20; size:16; signed:0;
field:u64 serial; offset:40; size:8; signed:0;
field:u32 hdr_flags; offset:48; size:4; signed:0;
field:u16 hdr_handle; offset:52; size:2; signed:0;
field:u16 hdr_related_handle; offset:54; size:2; signed:0;
field:u64 hdr_timestamp; offset:56; size:8; signed:0;
field:u8 hdr_length; offset:64; size:1; signed:0;
field:u8 hdr_maint_op_class; offset:65; size:1; signed:0;
field:u8 hdr_maint_op_sub_class; offset:66; size:1; signed:0;
field:u64 dpa; offset:72; size:8; signed:0;
field:u8 descriptor; offset:80; size:1; signed:0;
field:u8 type; offset:81; size:1; signed:0;
field:u8 sub_type; offset:82; size:1; signed:0;
field:u8 transaction_type; offset:83; size:1; signed:0;
field:u8 channel; offset:84; size:1; signed:0;
field:u32 device; offset:88; size:4; signed:0;
field:u8 comp_id[16]; offset:92; size:16; signed:0;
field:u64 hpa; offset:112; size:8; signed:0;
field:uuid_t region_uuid; offset:120; size:16; signed:0;
field:u16 validity_flags; offset:136; size:2; signed:0;
field:u8 rank; offset:138; size:1; signed:0;
field:u8 dpa_flags; offset:139; size:1; signed:0;
field:__data_loc char[] region_name; offset:140; size:4; signed:0;
field:u8 cme_threshold_ev_flags; offset:144; size:1; signed:0;
field:u32 cme_count; offset:148; size:4; signed:0;

print fmt: "memdev=%s host=%s serial=%lld log=%s : time=%llu uuid=%pUb len=%d flags='%s' handle=%x related_handle=%x maint_op_class=%u maint_op_sub_class=%u : dpa=%llx dpa_flags='%s' descriptor='%s' type='%s' sub_type='%s' transaction_type='%s' channel=%u rank=%u device=%x validity_flags='%s' comp_id=%s comp_id_pldm_valid_flags='%s' pldm_entity_id=%s pldm_resource_id=%s hpa=%llx region=%s region_uuid=%pUb cme_threshold_ev_flags='%s' cme_count=%x", __get_str(memdev), __get_str(host), REC->serial, __print_symbolic(REC->log, { CXL_EVENT_TYPE_INFO, "Informational" }, { CXL_EVENT_TYPE_WARN, "Warning" }, { CXL_EVENT_TYPE_FAIL, "Failure" }, { CXL_EVENT_TYPE_FATAL, "Fatal" }), REC->hdr_timestamp, &REC->hdr_uuid, REC->hdr_length, __print_flags(REC->hdr_flags, " | ", { ((((1UL))) << (2)), "PERMANENT_CONDITION" }, { ((((1UL))) << (3)), "MAINTENANCE_NEEDED" }, { ((((1UL))) << (4)), "PERFORMANCE_DEGRADED" }, { ((((1UL))) << (5)), "HARDWARE_REPLACEMENT_NEEDED" }, { ((((1UL))) << (6)), "MAINT_OP_SUB_CLASS_VALID" } ), REC->hdr_handle, REC->hdr_related_handle, REC->hdr_maint_op_class, REC->hdr_maint_op_sub_class, REC->dpa, __print_flags(REC->dpa_flags, "|", { ((((1UL))) << (0)), "VOLATILE" }, { ((((1UL))) << (1)), "NOT_REPAIRABLE" } ), __print_flags(REC->descriptor, "|", { ((((1UL))) << (0)), "UNCORRECTABLE_EVENT" }, { ((((1UL))) << (1)), "THRESHOLD_EVENT" }, { ((((1UL))) << (2)), "POISON_LIST_OVERFLOW" } ), __print_symbolic(REC->type, { 0x00, "ECC Error" }, { 0x01, "Invalid Address" }, { 0x02, "Data Path Error" }, { 0x03, "TE State Violation" }, { 0x04, "Scrub Media ECC Error" }, { 0x05, "Adv Prog CME Counter Expiration" }, { 0x06, "CKID Violation" } ), __print_symbolic(REC->sub_type, { 0x00, "Not Reported" }, { 0x01, "Internal Datapath Error" }, { 0x02, "Media Link Command Training Error" }, { 0x03, "Media Link Control Training Error" }, { 0x04, "Media Link Data Training Error" }, { 0x05, "Media Link CRC Error" } ), __print_symbolic(REC->transaction_type, { 0x00, "Unknown" }, { 0x01, "Host Read" }, { 0x02, "Host Write" }, { 0x03, "Host Scan Media" }, { 0x04, "Host Inject Poison" }, { 0x05, "Internal Media Scrub" }, { 0x06, "Internal Media Management" }, { 0x07, "Internal Media Error Check Scrub" }, { 0x08, "Media Initialization" } ), REC->channel, REC->rank, REC->device, __print_flags(REC->validity_flags, "|", { ((((1UL))) << (0)), "CHANNEL" }, { ((((1UL))) << (1)), "RANK" }, { ((((1UL))) << (2)), "DEVICE" }, { ((((1UL))) << (3)), "COMPONENT" }, { ((((1UL))) << (4)), "COMPONENT PLDM FORMAT" } ), __print_hex(REC->comp_id, 0x10), __print_flags(REC->comp_id[0], " | ", { ((((1UL))) << (0)), "PLDM Entity ID" }, { ((((1UL))) << (1)), "Resource ID" } ), (REC->validity_flags & ((((1UL))) << (3)) && REC->validity_flags & ((((1UL))) << (4))) ? (REC->comp_id[0] & ((((1UL))) << (0))) ? __print_hex(&REC->comp_id[1], 6) : "0x00" : "0x00", (REC->validity_flags & ((((1UL))) << (3)) && REC->validity_flags & ((((1UL))) << (4))) ? (REC->comp_id[0] & ((((1UL))) << (1))) ? __print_hex(&REC->comp_id[7], 4) : "0x00" : "0x00", REC->hpa, __get_str(region_name), &REC->region_uuid, __print_flags(REC->cme_threshold_ev_flags, "|", { ((((1UL))) << (0)), "Corrected Memory Errors in Multiple Media Components" }, { ((((1UL))) << (1)), "Exceeded Programmable Threshold" } ), REC->cme_count