Re: [PATCH v4 2/2] efi: an sysfs interface for user to update efi firmware

Andy Lutomirski
2015-04-27T21:59:58Z

On Fri, Apr 24, 2015 at 8:16 AM, James Bottomley
<James.Bottomley@hansenpartnership.com> wrote:
> On Fri, 2015-04-24 at 02:14 +0000, Kweh, Hock Leong wrote:
>> > -----Original Message-----
>> > From: James Bottomley [mailto:James.Bottomley@HansenPartnership.com]
>> > Sent: Thursday, April 23, 2015 10:10 PM
>> >
>> > On Thu, 2015-04-23 at 08:30 +0000, Kweh, Hock Leong wrote:
>> > > > -----Original Message-----
>> > > > From: James Bottomley
>> > [mailto:James.Bottomley@HansenPartnership.com]
>> > > > Sent: Wednesday, April 22, 2015 11:19 PM
>> > > >
>> > > >
>> > > > Yes, I think we've all agreed we can do it ... it's now a question of whether
>> > we
>> > > > can stomach the ick factor of actually initiating a transaction in close ... I'm
>> > still
>> > > > feeling queasy.
>> > >
>> > > The file "close" here can I understand that the file system will call the
>> > "release"
>> > > function at the file_operations struct?
>> > > http://lxr.free-electrons.com/source/include/linux/fs.h#L1538
>> > >
>> > > So, James you are meaning that we could initiating the update transaction
>> > > inside the f_ops->release() and return the error code if update failed in this
>> > > function?
>> >
>> > Well, that's what I was thinking. However the return value of ->release
>> > doesn't get propagated in sys_close (or indeed anywhere ... no idea why
>> > it returns an int) thanks to the task work additions, so we'd actually
>> > have to use the operation whose value is propagated in sys_close() which
>> > turns out to be flush.
>> >
>> > James
>> >
>>
>> Okay, I think I got you. Just to double check for in case: you are meaning
>> to implement it at f_ops->flush() instead of f_ops->release().
>
> Well, what I'm saying is that the only way to propagate an error to
> close is by returning one from the flush file_operation.
>
> Let's cc fsdevel to see if they have any brighter ideas.
>
> The problem is we need to update firmware (several megabytes of it) via
> standard system tools. We're thinking cat to a device. The problem is
> that we need an error code back once the update goes through (which it
> can't until we've fed all the firmware data into the system). To use
> standard unix tools, we have to trigger off the standard system calls
> cat uses and since write() will happen in chunks, the only way to commit
> the transaction is in close().
>
> We initially through of initiating the transaction in f_ops->release and
> returning the error code there, but that doesn't work because its value
> isn't actually propagated, so we're now thinking of initiating the
> transaction in f_ops->flush instead (this is a device, not a file, so it
> won't get any other flushers). Are there any other ways for us to
> propagate error on close?
>

I think we may end up wanting to support both UpdateCapsule and
QueryCapsuleCapabilities, in which case this gets awkward. Maybe we
really should do a misc device + ioctl.

--Andy