dev-null: The "read" function has to return 0 if nothing has been read
dev-null: The "read" function has to return 0 if nothing has been read

The "read" function of the dev-null device currently claims that
the same amount of bytes has been read as input bytes have been
requested. This causes grub to hang forever at the boot selection
menu, since grub then thinks that there's a continuous stream of input
data. If nothing has been read (which is always the case for the
dev-null device), the "read" function should simply return 0 instead.
Then grub also boots properly again after the typical short timeout.

Reported-by: Laurent Vivier <240b731be4efaffb85b5d13af681c07e7ef8ddcb@redhat.com>
Signed-off-by: Thomas Huth <9e65be74847981e55b2564b6266c57d86d3bac05@redhat.com>
Tested-by: Laurent Vivier <240b731be4efaffb85b5d13af681c07e7ef8ddcb@redhat.com>
Signed-off-by: Alexey Kardashevskiy <ac1fc56530d7d037e1ea666f130daca22d72f964@ozlabs.ru>
Signed-off-by: Nikunj A Dadhania <e2f4a5db9b4735182a88051d1e7a3599f9eac9db@linux.vnet.ibm.com>

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