[PATCH] disk/efi: skip iPXE dummy block devices

[Andrei Borzenkov <arvidjaar@gmail.com>]

iPXE adds Simple File System Protocol to loaded image handle, as side
effect it also adds Block IO protocol (according to comments, to work
around some bugs in EDK2). GRUB assumes that every device with Block IO
is disk and skips network initialization entirely. But iPXE Block IO
implementation is just a stub which always fails for every operation
so cannot be used. Attempt to detect and skip such devices.

We are using media ID which iPXE sets to "iPXE" and block IO size in
hope that no real device would announce 1B block ...

Closes: 50518

@Vladimir, @Daniel - this is probably 2.02 material. We cannot use
any device that advertises block size less than 512B anyway, so it
should not cause regression for disk boot.

It is my fault, I have seen it earlier but was busy with another problem
so just worked around it to continue testing.

---
 grub-core/disk/efi/efidisk.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/grub-core/disk/efi/efidisk.c b/grub-core/disk/efi/efidisk.c
index 3b79f7b..47a4e99 100644
--- a/grub-core/disk/efi/efidisk.c
+++ b/grub-core/disk/efi/efidisk.c
@@ -80,6 +80,15 @@ make_devices (void)
 	/* This should not happen... Why?  */
 	continue;
 
+      /* iPXE adds stub Block IO protocol to loaded image device handle. It is
+         completely non-functional and simply returns an error for every method.
+	 So attempt to detect and skip it. Magic number is literal "iPXE" and
+	 check block size as well */
+      /* FIXME: shoud we close it? We do not do it elsewhere */
+      if (bio->media && bio->media->media_id == 0x69505845U &&
+	  bio->media->block_size == 1)
+	  continue;
+
       d = grub_malloc (sizeof (*d));
       if (! d)
 	{
-- 
tg: (bcf3c55..) bug/50518 (depends on: master)