Re: [PATCH 1/1] efi_loader: CloseProtocol in efi_fmp_find

[AKASHI Takahiro <takahiro.akashi@linaro.org>]

On Tue, Oct 11, 2022 at 07:58:11AM +0200, Heinrich Schuchardt wrote:
> 
> 
> On 10/11/22 02:49, AKASHI Takahiro wrote:
> > The commit message is not accurate.
> > 
> > On Fri, Oct 07, 2022 at 04:06:23PM +0200, Heinrich Schuchardt wrote:
> > > The CloseProtocol() boot service requires a handle as first argument.
> > > Passing the protocol interface is incorrect.
> > 
> > Correct, but
> > 
> > > CloseProtocol() only has an effect if called with a non-zero value for
> > > agent_handle. HandleProtocol() uses an opaque agent_handle when invoking
> > > OpenProtocol() (currently NULL).
> > 
> > No. OpenProtocol() is called with efi_root as an agent handle.
> > So, calling CloseProtocol() is a right thing at the end.
> 
> Typically an agent handle is used to relate to a driver exposing the driver
> binding protocol.

Why can't we, other than a driver, call HandleProtocol()
as a convenient way of accessing an interface?

> The root node does not expose the driver binding protocol.

So do you mean the current implementation of HandleProtocol() is wrong?

> Why would you want to create an open protocol information entry here?

To access get_image_info() quickly.

> Do you think anything with the code after the patch is wrong?

No reason to replace handle_protocol().

Another example is here:
efi_load_image_from_path()
    efi_handle_protocol(device, guid, (void **)&load_file_protocol));
    ...
    efi_close_protocol(device, guid, efi_root, NULL);

I believe that this function is anything but a driver.
I think using HandleProtocol() (or preferably OpenProtocol()) and CloseProtocol()
in pair seems totally sane.

-Takahiro Akashi



> Best regards
> 
> Heinrich
> 
> > 
> > > Therefore HandleProtocol() should be
> > > avoided.
> > > 
> > > * Replace the LocateHandle() call by efi_search_protocol().
> > 
> > LocateHandle() -> efi_handle_protocol()
> > 
> > So you could have fixed this way:
> >      EFI_CALL(efi_close_protocol(handle, ..., &efi_root, NULL);
> > 
> > I preferred to use EFI_CALL() over this file as you can see.
> > 
> > -Takahiro Akashi
> > 
> > > * Remove the CloseProtocol() call.
> > > 
> > > Fixes: 8d99026f0697 ("efi_loader: capsule: support firmware update")
> > > Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
> > > ---
> > >   lib/efi_loader/efi_capsule.c | 14 ++++++--------
> > >   1 file changed, 6 insertions(+), 8 deletions(-)
> > > 
> > > diff --git a/lib/efi_loader/efi_capsule.c b/lib/efi_loader/efi_capsule.c
> > > index b6bd2d6af8..397e393a18 100644
> > > --- a/lib/efi_loader/efi_capsule.c
> > > +++ b/lib/efi_loader/efi_capsule.c
> > > @@ -159,12 +159,14 @@ efi_fmp_find(efi_guid_t *image_type, u8 image_index, u64 instance,
> > >   	efi_status_t ret;
> > >   	for (i = 0, handle = handles; i < no_handles; i++, handle++) {
> > > -		ret = EFI_CALL(efi_handle_protocol(
> > > -				*handle,
> > > -				&efi_guid_firmware_management_protocol,
> > > -				(void **)&fmp));
> > > +		struct efi_handler *fmp_handler;
> > > +
> > > +		ret = efi_search_protocol(
> > > +				*handle, &efi_guid_firmware_management_protocol,
> > > +				&fmp_handler);
> > >   		if (ret != EFI_SUCCESS)
> > >   			continue;
> > > +		fmp = fmp_handler->protocol_interface;
> > >   		/* get device's image info */
> > >   		info_size = 0;
> > > @@ -215,10 +217,6 @@ efi_fmp_find(efi_guid_t *image_type, u8 image_index, u64 instance,
> > >   skip:
> > >   		efi_free_pool(package_version_name);
> > >   		free(image_info);
> > > -		EFI_CALL(efi_close_protocol(
> > > -				(efi_handle_t)fmp,
> > > -				&efi_guid_firmware_management_protocol,
> > > -				NULL, NULL));
> > >   		if (found)
> > >   			return fmp;
> > >   	}
> > > -- 
> > > 2.37.2
> > >