bd9e9916c3
The NBD spec was recently changed [1] to refer to the opaque client identifier as a 'cookie' rather than a 'handle', but has for a much longer time listed it as a 64-bit value, and declares that all values in the NBD protocol are sent in network byte order (big-endian). Because the value is opaque to the server, it doesn't usually matter what endianness we send as the client - as long as we are consistent that either we byte-swap on both write and read, or on neither, then we can match server replies back to our requests. That said, our internal use of the cookie is as a 64-bit number (well, as two 32-bit numbers concatenated together), rather than as 8 individual bytes; so prior to this commit, we ARE leaking the native endianness of our internals as a client out to the server. We don't know of any server that will actually inspect the opaque value and behave differently depending on whether a little-endian or big-endian client is sending requests, but since we DO log the cookie value, a wireshark capture of the network traffic is easier to correlate back to the kernel traffic of a big-endian host (where the u64 and char[8] representations are the same) than of a little-endian host (where if wireshark honors the NBD spec and displays a u64 in network byte order, it is byte-swapped from what the kernel logged). The fix in this patch is thus two-part: it now consistently uses network byte order for the opaque value (no difference to a big-endian machine, but an extra byteswap on a little-endian machine; probably in the noise compared to the overhead of network traffic in general), and now uses a 64-bit integer instead of char[8] as its preferred access to the opaque value (direct assignment instead of memcpy()). Signed-off-by: Eric Blake <eblake@redhat.com> Reviewed-by: Josef Bacik <josef@toxicpanda.com> Link: https://lore.kernel.org/r/20230410180611.1051618-4-eblake@redhat.com Signed-off-by: Jens Axboe <axboe@kernel.dk>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.