Messages in this thread | | | Date | Mon, 17 Oct 2022 13:21:43 -0400 | From | Steven Rostedt <> | Subject | Re: [RFC V2 PATCH 05/11] cxl/mem: Trace General Media Event Record |
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On Mon, 17 Oct 2022 17:37:17 +0100 Jonathan Cameron <Jonathan.Cameron@huawei.com> wrote:
> Looking at other similar cases though and we have a lot of use > of trace_seq_printf() e.g. libata_trace_parse_status() though note > there is some magic macro stuff in include/trace/events/libata.h > to tie that together. > https://elixir.bootlin.com/linux/latest/source/drivers/ata/libata-trace.c#L14 > > That seems to get you access to the actual buffer we are printing into > in similar cases.
Looking at the code you linked to, I wonder why __print_flags() wasn't used?
For instance, you have:
const char * libata_trace_parse_status(struct trace_seq *p, unsigned char status) { const char *ret = trace_seq_buffer_ptr(p);
trace_seq_printf(p, "{ "); if (status & ATA_BUSY) trace_seq_printf(p, "BUSY "); if (status & ATA_DRDY) trace_seq_printf(p, "DRDY "); if (status & ATA_DF) trace_seq_printf(p, "DF "); if (status & ATA_DSC) trace_seq_printf(p, "DSC "); if (status & ATA_DRQ) trace_seq_printf(p, "DRQ "); if (status & ATA_CORR) trace_seq_printf(p, "CORR "); if (status & ATA_SENSE) trace_seq_printf(p, "SENSE "); if (status & ATA_ERR) trace_seq_printf(p, "ERR "); trace_seq_putc(p, '}'); trace_seq_putc(p, 0);
return ret; }
Which is just a re-implementation of:
__print_flags(status, " ", { ATA_BUSY, "BUSY" }, { ATA_DRDY, "DRDY" }, { ATA_DF, "DF" }, { ATA_DSC, "DSC" }, { ATA_DRQ, "DRQ" }, { ATA_CORR, "CORR" }, { ATA_SENSE, "SENSE" }, { ATA_ERR, "ERR" })
The major difference between the two, is that libtraceevent will be able to parse the above and convert the status bits into strings, whereas using libata_trace_parse_status() will just give you a parsing error.
That is, perf and trace-cmd will not be able to parse it unless you write a separate plugin for libtraceevent to do it but that means you'll have duplicate code.
I know you just want echo and cat, but that will still work, and this will make it work for the tooling as well.
-- Steve
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