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

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Message-ID: <CALCETrU2G10uGvdB6kVyfMPA=biuZwK7BAeqmKuY=jvN38K2wA@mail.gmail.com>
Date:	Mon, 27 Apr 2015 14:59:31 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	James Bottomley <James.Bottomley@...senpartnership.com>
Cc:	"Kweh, Hock Leong" <hock.leong.kweh@...el.com>,
	Peter Jones <pjones@...hat.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	Ming Lei <ming.lei@...onical.com>,
	"Ong, Boon Leong" <boon.leong.ong@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	Sam Protsenko <semen.protsenko@...aro.org>,
	Roy Franz <roy.franz@...aro.org>,
	Borislav Petkov <bp@...en8.de>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v4 2/2] efi: an sysfs interface for user to update efi firmware

On Fri, Apr 24, 2015 at 8:16 AM, James Bottomley
<James.Bottomley@...senpartnership.com> wrote:
> On Fri, 2015-04-24 at 02:14 +0000, Kweh, Hock Leong wrote:
>> > -----Original Message-----
>> > From: James Bottomley [mailto:James.Bottomley@...senPartnership.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@...senPartnership.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
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