dbf637ff39
For legacy reasons NFP FW may be compiled to DMA packets to a constant
offset into the buffer and use the space before it for metadata. This
ensures that packets data always start at a certain offset regardless of
the amount of preceding metadata.
If rx offset is set to 0 there may still be up to 64 bytes of metadata
but metadata will start at the beginning of the buffer, instead of:
data_start_offset = rx_offset - meta_len
Even though we make the buffers larger to accommodate up to 64 bytes of
metadata, if there is only N bytes of metadata, we will end up with
N bytes of headroom and 64 - N bytes of tailroom. Therefore we can't
rely on that space for XDP headroom. Make sure we always allocate
full 256 bytes. This, unfortunately, means we can't fit the headroom
on an u8 any more.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.