Re: [PATCH 3/5] MdeModulePkg/UefiBootManagerLib: report EDKII_OS_LOADER_DETAIL status code

["Ni, Ruiyu" <ruiyu.ni@intel.com>]

Sent from a small-screen device

在 2017年11月24日，上午1:08，Laszlo Ersek <lersek@redhat.com<mailto:lersek@redhat.com>> 写道：

On 11/23/17 15:53, Ni, Ruiyu wrote:
Comments below.

-----Original Message-----
From: Laszlo Ersek [mailto:lersek@redhat.com]
Sent: Thursday, November 23, 2017 10:03 PM
To: Ni, Ruiyu <ruiyu.ni@intel.com<mailto:ruiyu.ni@intel.com>>; edk2-devel-01 <edk2-devel@lists.01.org<mailto:edk2-devel@lists.01.org>>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org<mailto:ard.biesheuvel@linaro.org>>; Justen, Jordan L
<jordan.l.justen@intel.com<mailto:jordan.l.justen@intel.com>>; Dong, Eric <eric.dong@intel.com<mailto:eric.dong@intel.com>>; Zeng, Star
<star.zeng@intel.com<mailto:star.zeng@intel.com>>; Doran, Mark <mark.doran@intel.com<mailto:mark.doran@intel.com>>
Subject: Re: [PATCH 3/5] MdeModulePkg/UefiBootManagerLib: report
EDKII_OS_LOADER_DETAIL status code

Hello Ray,

(CC Mark Doran for the last part of my email)

On 11/23/17 06:21, Ni, Ruiyu wrote:
Laszlo,
When booting a boot option, UefiBootManagerBoot() sets a Boot####
variable and saves #### to BootCurrent variable.
So all the details (except the EDKII_OS_LOADER_DETAIL.Status) can be
retrieved from reading Boot#### variable.

I have two counter-arguments:

(1) I would like to minimize the number of accesses to non-volatile UEFI
variables. Dependent on the virtualization platform and the (virtual) flash chip
structure (for example, flash block size), flash access can be very slow.

I'm not 100% sure whether this performance problem affects flash *reads* as
well, or if it affects flash writes only. (It definitely affects flash writes.)

NV *read* should have no performance impact since EDKII variable driver's
implementation caches the flash in memory. I am not sure about that
in OVMF.

Yeah it should work the same. Thanks!

But I think a good implementation of variable driver should
consider such *read* optimization.
Performance needs to be considered, but simpler/easy-maintain
code takes higher priority.



(2) The delivery of status codes to registered handlers is asynchronous, not
synchronous. Handlers are registered at various task priority levels, and if the
reporting occurs at the same or higher TPL, then the delivery will be delayed.
(According to the PI spec, it is even possible to report several status codes
before the first will be delivered -- basically the codes are queued until the TPL is
reduced sufficiently.) This is why all data has to be embedded in the status code
structure itself.

Like in any other notify function's case, it is prudent to register status code
handlers at the least strict TPL that can work for the actual processing. (The
internals of the handler function can even put an upper limit on the TPL; for
example using Simple Text Output prevents us from going higher than
TPL_NOTIFY.) For this reason I chose TPL_CALLBACK for the OVMF status code
handler.

Now, if we can *guarantee* that these status codes are only reported at the
TPL_APPLICATION level, then a TPL_CALLBACK status code handler will be
synchronous in effect, and then the status code structure can carry references
to other (external) things in the system too, such as UEFI variables.

Can we guarantee that EfiBootManagerBoot() is never invoked above
TPL_APPLICATION?
Yes. It should be. Because gBS->LoadImage()/StartImage() per UEFI spec TPL
restriction rule, should be run at TPL_APPLICATION.
And if there is no special reason (handler runs too slow), the status handler
is registered at TPL_HIGH so that the handler is called synchronously.

OK, the TPL_APPLICATION promise will work for me. I missed the LoadImage
/ StartImage implications; good point!

(I can't register the handler at TPL_HIGH, because the handler calls
AsciiPrint, which internally uses gST->ConOut, and that (i.e.,
SimpleTextOut) cannot be used above TPL_NOTIFY. But the TPL_CALLBACK
handler will work fine with the TPL_APPLICATION report.)

TPL_HIGH is just an indicator to tell status router to call the handler in blocking or synchronized way. So handler actually works in the status code reporter’s TPL, which is TPL_APPLICATION.






4 more comments below.

[snip]

+      BmReportOsLoaderDetail (
+        OsLoaderDetail,
+        OsLoaderDetailSize,
+        EDKII_OS_LOADER_DETAIL_TYPE_LOAD,
+        0                                 // DetailStatus -- unused here
+        );
+

1. With the BootCurrent, this change is not necessary because others
can hook PcdProgressCodeOsLoaderLoad to get the current loading boot
option.

As long as we can clear my points (1) and (2) above, I'd be fine with this
approach.


      Status = gBS->LoadImage (
                      TRUE,
                      gImageHandle,
                      FilePath,
                      FileBuffer,
                      FileSize,
                      &ImageHandle
                      );
    }
    if (FileBuffer != NULL) {
      FreePool (FileBuffer);
    }
    if (FilePath != NULL) {
      FreePool (FilePath);
    }

    if (EFI_ERROR (Status)) {
      //
      // Report Status Code to indicate that the failure to load boot option
      //
      REPORT_STATUS_CODE (
        EFI_ERROR_CODE | EFI_ERROR_MINOR,
        (EFI_SOFTWARE_DXE_BS_DRIVER |
EFI_SW_DXE_BS_EC_BOOT_OPTION_LOAD_ERROR)
        );
+      BmReportOsLoaderDetail (
+        OsLoaderDetail,
+        OsLoaderDetailSize,
+        EDKII_OS_LOADER_DETAIL_TYPE_LOAD_ERROR,
+        Status
+        );
+

2. I think firstly, the OsLoaderDetail is not needed.
Secondly, I prefer to submit a PI spec change to include extended data
for EFI_SW_DXE_BS_EC_BOOT_OPTION_LOAD_ERROR status code.
Instead of inventing a new status code.

I understand your point, and in theory I agree with it, but in practice, I cannot.

If there is no similar status code for a certain purpose, I agree to invent a new status
code. And when the new status code is proven by time to be mature enough, it can go
to PI spec.
But for this case, since PI spec already has such status code, I prefer to at least try
to change the spec. If PIWG doesn't agree, we can go on using the new status code.

Oh I'm not worried about PIWG disagreement. Getting strong disagreement
*quickly* is actually a very good outcome, because it tells us how to
proceed.

What I'm worried about is a drawn-out process that takes forever (and
requires me to spend a disproportionate amount of time on the phone, and
at bad times).

Unless there is some kind of promise that I can work with the PIWG in a
timely manner *without* the phone, it doesn't make sense for me to start
the process. I'll ask on the PIWG list first.

Thanks,
Laszlo



My experience with Mantis tickets is not good:

(a) First, I would have to write up the proposal. That's fine, I can do that; have
done it before.


(b) Second, I'd have to *call* the meetings. Please locate the email titled

 a reminder about MANTIS usage

from Mark, (date: 6 Sep 2017), cross-posted to the PIWG/USWG/ASWG lists.

I'm not allowed to quote the email verbatim -- all of these lists are confidential -
-, but if you look up the paragraph starting with "Best practice", Mark basically
implied, "file the the Mantis ticket, then dial in to the next meeting and sell your
proposal to the WG *verbally*".

I *cannot* do that. The WG meetings always take place early afternoon in
Pacific (US West Coast) timezone, which is around *midnight* in my timezone.

In addition, I don't even have time to attend the confcalls that I'm invited to
within Red Hat!

I don't understand why a carefully written Mantis ticket is not sufficient for
discussion, but apparently it isn't. :/


(c) Case in point, please see Mantis ticket #1736, titled

   lacking specification of EFI_BOOT_SCRIPT_WIDTH in PI 1.5 / Vol 5 /
   8.7.1 Save State Write

which I had originally filed in December 2016.

In February 2017, I was asked for more details. I said, "fair enough", and I spent
half a day writing up the requested change in *full* detail.
I gave editing instructions of the form

 change this to that

and

 add/delete the following

as recommended in Mark's email (b).

You can see my write-up in note 0005044. After that note, there have been
*zero* updates to the ticket; since February 2017.


So the fact is, unless you have time to call the WG meetings every week, and
push *live* for the change that you want, you have no chance at getting stuff
into the specs.


I mean, in his email (b), Mark suggests asking a "proxy" for representing the
change request, to anyone that cannot dial in. Well, can *you* be my proxy on
the PIWG meeting, if I write up the change request? You certainly understand
the problem space, and you maintain the corresponding reference code in edk2.
I just doubt you have time for conference calls, same as I.

UefiBootManagerLib already reports an extended status code, with
EDKII_SET_VARIABLE_STATUS payload. Introducing another edk2-specific status
code requires no slow negotiation, and it can be adopted by others, in practice,
if they like it. Once it is wide-spread practice, it can be more easily codified in
the spec. The specifics for the first implementation can be -- should be --
discussed on this open list; we had better not standardize something that has
zero implementations just yet.

Anyway, I'm willing to go through the standardization process, but only if it
doesn't require me to pick up the phone every week (esp. at midnight).

Thanks
Laszlo