[PATCH 0/7] net/9p: remove msize limit in virtio transport

This is an initial draft for getting rid of the current 500k 'msize'
limitation in the 9p virtio transport, which is currently a bottleneck for
performance of Linux 9p mounts.

This is a follow-up of the following series and discussion:
https://lore.kernel.org/all/28bb651ae0349a7d57e8ddc92c1bd5e62924a912.1630770829.git.linux_oss@crudebyte.com/T/#eb647d0c013616cee3eb8ba9d87da7d8b1f476f37 (local)

Known limitation: With this series applied I can run

  QEMU host <-> 9P virtio <-> Linux guest

with up to 3 MB msize. If I try to run it with 4 MB it seems to hit some
limitation on QEMU side:

  qemu-system-x86_64: virtio: too many write descriptors in indirect table

I haven't looked into this issue yet.

Testing and feedback appreciated!

Christian Schoenebeck (7):
  net/9p: show error message if user 'msize' cannot be satisfied
  9p/trans_virtio: separate allocation of scatter gather list
  9p/trans_virtio: turn amount of sg lists into runtime info
  9p/trans_virtio: introduce struct virtqueue_sg
  net/9p: add trans_maxsize to struct p9_client
  9p/trans_virtio: support larger msize values
  9p/trans_virtio: resize sg lists to whatever is possible

 include/net/9p/client.h |   2 +
 net/9p/client.c         |  18 ++-
 net/9p/trans_virtio.c   | 281 ++++++++++++++++++++++++++++++++++------
 3 files changed, 261 insertions(+), 40 deletions(-)

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2.20.1