The existing write_slice() method is a wrapper around copy_to_user() and
expects the user buffer to be larger than the source buffer.
However, userspace may split up reads in multiple partial operations
providing an offset into the source buffer and a smaller user buffer.
In order to support this common case, provide a helper for partial
writes.
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Matthew Maurer <mmaurer@google.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
[ Replace map_or() with let-else; use saturating_add(). - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
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