I think this behavior is raised by the grub search command in memdisk:
1. in the reproducing step 8, press e and then press F2 to make ourselves to be
dropped into the grub shell
2. cat (memdisk)/grub.cfg, shows
grub shell> cat (memdisk)/grub.cfg
if ! search --file --set=root /.disk/info: then
search --file --set=root /.disk/minu-info
fi
set prefix=($root)/boot/grub
if [ -e $prefix/x86_64-efi/grub.cfg ]; then
source $prefix/x86_64-efi/grub.cfg
else
source $prefix/grub.cfg
fi
3. investigate the search behavior,
it seems that grub iterates hd before cd always.
grub-core/disk/efi/efidisk.c
static int
grub_efidisk_iterate (int (*hook) (const char *name))
{
struct grub_efidisk_data *d;
char buf[16];
int count;
for (d = fd_devices, count = 0; d; d = d->next, count++)
{
grub_snprintf (buf, sizeof (buf), "fd%d", count);
grub_dprintf ("efidisk", "iterating %s\n", buf);
if (hook (buf))
>.......return 1;
}
for (d = hd_devices, count = 0; d; d = d->next, count++)
{
grub_snprintf (buf, sizeof (buf), "hd%d", count);
grub_dprintf ("efidisk", "iterating %s\n", buf);
if (hook (buf))
>.......return 1;
}
for (d = cd_devices, count = 0; d; d = d->next, count++)
{
grub_snprintf (buf, sizeof (buf), "cd%d", count);
grub_dprintf ("efidisk", "iterating %s\n", buf);
if (hook (buf))
>.......return 1;
}
return 0;
}
4. usb will be regarded as hd device, so the search command always set
the variable root as usb (more precisely, any other hard disk devices
with .disk/info) instead of our selection, DVD
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https://bugs.launchpad.net/bugs/1198846
Title:
[efi boot to unexpected media] plug in live usb and DVD at the same
time, try to boot from DVD but it comes to usb
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