How best to get the size of a blockdev from a file?

[David Howells <dhowells@xxxxxxxxxx>]

Hi Christoph,

It seems that my use of i_size_read(file_inode(in)) in filemap_splice_read()
to get the size of the file to be spliced from doesn't work in the case of
blockdevs and it always returns 0.

What would be the best way to get the blockdev size?  Look at
file->f_mapping->i_size maybe?

David