Hi, On Tue, 27 Sept 2022 at 00:53, Heinrich Schuchardt <heinrich.schucha...@canonical.com> wrote: > > > > On 9/27/22 03:51, AKASHI Takahiro wrote: > > On Mon, Sep 26, 2022 at 08:06:52AM +0200, Heinrich Schuchardt wrote: > >> > >> > >> On 9/16/22 02:58, AKASHI Takahiro wrote: > >>> On Thu, Sep 15, 2022 at 10:02:40PM +0200, Heinrich Schuchardt wrote: > >>>> The medium a device like 'mmc 0' or 'usb 0' points to may change over > >>>> time. Hence device type and number are not sufficient to identify the > >>>> inserted medium. The same is true for the device path generated for > >>>> such a device. > >>> > >>> Well, it depends on how a device path is generated in U-Boot's UEFI > >>> implementation. I believe that a device path represents an "unique path" > >>> to a given device however this device is enumerated. > >>> In this sense, the current dp_fill()/efi_dp_from_part() is not a right > >>> implementation as it relies on device numbers. > >>> Furthermore, a generated device path here is different from one generated > >>> by EDK2 (even if both software are run on the same board). > >>> > >>> This is an issue that I used to tackle in > >>> https://lists.denx.de/pipermail/u-boot/2021-November/468216.html > >>> although I have since had no progress. > >>> > >>>> This is why the EFI_BLOCK_IO_PROTOCOL provides a field > >>>> MediaId. > >>>> > >>>> Whenever a removable medium is changed or a new block device with a > >>>> previously used device path is created we should provide a different > >>>> MediaID. > >>>> > >>>> This series adds a field media_id to the block device descriptor and > >>>> fills > >>>> it after probing. The value of the field is then copied to the > >>>> EFI_BLOCK_IO_PROTOCOL. > >>> > >>> I'm afraid that your patch doesn't always work as you expect. > >>> When "scsi rescan" or "usb stop; usb start", for instance, is invoked, > >>> all the existing devices and associated blk_desc structures are once freed > >>> and even if nothing is changed, i.e. a device is neither removed nor > >>> added, > >>> the exact same structures will be re-created. > >>> With your patch applied, however, a new (and different) "media_id" will be > >>> assigned to an existing device. UEFI User may be notified of "media > >>> change". > >>> (To be honest, this is quite unlikely because the current UEFI > >>> implementation > >>> doesn't use BLOCK_IO_PROTOCOL internally, say, for file system access.) > >> > >> This behavior matches what EDK II does if you remove a device and create a > >> new device. > > > > I don't think that EDK2 has "scsi rescan" or others, which users can invoke > > at any time. Moreover, I believe that EDK2 code (drivers) checks whether a > > device > > is really changed or not before updating a MediaId. > > > >> If a device is removed and recreated anything could have happened in > >> between > >> like complete repartitioning. We cannot assume that any cached state is > >> valid anymore even if GUIDs are the same. > > > > I'm not sure if you fully understand my point. > > My assumption is the case where a device is NOT removed around "scsi rescan" > > (or usb stop/start) and stays online. In this case, > > 1. access to, say, "scsi 0:1", via UEFI BLOCK_IO succeeds > > 2. "scsi rescan" > > 3. access to the same device, "scsi 0:1", via UEFI BLOCK_IO > > currently (3) succeeds, but with your patch, it may potentially fail because > > of media_id altered. > > > > I admit that it will not happen under the current UEFI implementation > > because > > non of UEFI applications will survive across command lines and none of > > information, > > including media_id or handle, can be carried over from (1) to (3). > > But unconditionally incrementing an internally-held media_id, as in your > > patch, > > is a wrong behavior. > > The patch issues a new media ID if a new device is probed which only > happens to have the same device number if another device of that number > was removed before. > > Commands like 'usb scan' don't necessarily issue the same numbers to the > same device as before the command if a new device has been attached in > the meanwhile. > > Assuming that a new device contains the same medium as an old one > because by chance it has the same device number is definitively unsafe. > > If a device is probed, we have to assume that it contains a new medium.
Sorry if I repeat myself, but this sort of thing should be handled in the driver model code. Can we get some more progress on integrating the EFI layer better? Regards, Simon
