Unlike files accessed via a normal file system, the file->read_hook() is
not honoured when using blocklist notation.
This means that when trying to use a dedicated, 1 KiB, raw partition
for the environment block and hence does something like
save_env --file=(hd0,gpt9)0+2 X Y Z
this fails with "sparse file not allowed", which is rather unexpected,
as I've explicitly said exactly which blocks should be used. Adding
a little debugging reveals that grub_file_size(file) is 1024 as expected,
but total_length is 0, simply because the callback was never invoked, so
blocklists is an empty list.
Fix that by honouring the ->read_hook() set by the caller, also when
a "file" is specified with blocklist notation.
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Reviewed-by: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
