[v16,00/45] sg: add v4 interface

This patchset is the first stage of a two stage rewrite of the scsi
generic (sg) driver. The main goal of the first stage is to introduce
the sg v4 interface that uses 'struct sg_io_v4' as well as keeping and
modernizing the sg v3 interface (based on 'struct sg_io_hdr'). The
async interface formerly requiring the use of write() and read()
system calls now have ioctl(SG_IOSUBMIT) and ioctl(SG_IORECEIVE)
replacements.

A recent patch added support for blk_poll() and requests that
have REQ_HIPRI set. The blk_poll() additions are in patch 44 and
will compile. However, to use those additions one or more SCSI LLDs
are needed that support mq_poll(). For those, look to a patchset
from Kashyap Desai called "[PATCH v4 0/5] io_uring iopoll in scsi
layer" [20210215]. This patchset allows 'iopoll' requests to be
issued without io_uring (by setting SGV4_FLAG_HIPRI). A recent
patch to fio allows its sg engine to issue iopoll requests by
using hipri=1 in the fio script. One further note, an _async_
interface to blk_poll() is being proposed in this patchset.

For documentation see:
    http://sg.danny.cz/sg/sg_v40.html
for more details. If accessing http pages is a problem, a temporary
rendering of this page can be found here:
    https://doug-gilbert.github.io/sg_v40.html

This patchset is against Martin Petersen's 5.12/scsi-queue branch.

Changes since v15 (sent to linux-scsi list on 20210125)
  - tweak state machine which sets INFLIGHT state _before_
    blk_execute_rq_nowait() is called. Add a bit flag that indicates
    the logic flow has returned from that call. This guards against
    blk_poll() being called before the block layer has really
    launched the request.
  - fix bug clearing SG_FFD_HIPRI_SEEN bit as
    atomic_dec_and_test() returns true when the post-decrement value
    is zero, the opposite of what a C conditional does.

Changes since v14 (sent to linux-scsi list on 20210124)
  - two fixes based on report from Dan Carpenter and kernel test
    robot
  - fix Johannes Thumshirn's email address
  - separate patch issued on fio to add 'hipri' option to its sg
    engine. Enables fio to test new sg driver blk_poll() support

Changes since v13 (sent to linux-scsi list on 20210113)
  - fix obscure compile error reported by "kernel test robot
    <lkp@intel.com>"
  - harden code around blk_poll() invocation; needed based on
    fio testing
  - remove SG_FFD_MMAP_CALLED bit code after Hannes Reinecke pointed
    out it was redundant

Changes since v12 (sent to linux-scsi list on 20201115)
  - add blk_poll() support, prefix that patch's subject with 'RFC'

Changes since v11 (sent to linux-scsi list on 20201014)
  - no author originated changes since v11
  - port from lk 5.9.0-rc1 to lk 5.10.0-rc1 picks up a change to
    the import_iovec() which requires a change to patch 25/44
  - only publish this cover letter and v12 of patch 25/44 to
    the linux-scsi list. The other 43 patches remain as published
    on 20201014.

Changes since v10 (sent to linux-scsi list on 20200823)
  - unchanged: 0001 to 0009, 0010 to 0017
  - rename sg_add_req() to sg_setup_req() [0010]
  - patches 40,41,42 and 43 are new, see their commit messages
  - remove SG_RS_RCV_DONE request state leaving 3.5 states
    [the 0.5 state is SG_RS_BUSY]
  - rework sg_rq_chg_state() code that enforces request
    state changes and associated xarray marks
  - track lowest used and unused indexes in the request arrays so
    iterations over the request xarray are efficient. This is a
    significant saving when the iodepth queue length is large

Changes since v9 (sent to linux-scsi list on 20200421)
  - rebase on MKP's 5.10/scsi-queue branch
  - remove some master/slave terminology that had bled in from
    the part 2 patchset
  - change sg_request::start_ns type from ktime_t to u64
  - pick up several error path correction fixes applied to the
    sg driver by other authors

Changes since v8 to v1 in earlier patchsets
  - see: the v10 patchset sent to linux-scsi on 20200823


Douglas Gilbert (45):
  sg: move functions around
  sg: remove typedefs, type+formatting cleanup
  sg: sg_log and is_enabled
  sg: rework sg_poll(), minor changes
  sg: bitops in sg_device
  sg: make open count an atomic
  sg: move header to uapi section
  sg: speed sg_poll and sg_get_num_waiting
  sg: sg_allow_if_err_recovery and renames
  sg: improve naming
  sg: change rwlock to spinlock
  sg: ioctl handling
  sg: split sg_read
  sg: sg_common_write add structure for arguments
  sg: rework sg_vma_fault
  sg: rework sg_mmap
  sg: replace sg_allow_access
  sg: rework scatter gather handling
  sg: introduce request state machine
  sg: sg_find_srp_by_id
  sg: sg_fill_request_element
  sg: printk change %p to %pK
  sg: xarray for fds in device
  sg: xarray for reqs in fd
  sg: replace rq array with xarray
  sg: sense buffer rework
  sg: add sg v4 interface support
  sg: rework debug info
  sg: add 8 byte SCSI LUN to sg_scsi_id
  sg: expand sg_comm_wr_t
  sg: add sg_iosubmit_v3 and sg_ioreceive_v3 ioctls
  sg: add some __must_hold macros
  sg: move procfs objects to avoid forward decls
  sg: protect multiple receivers
  sg: first debugfs support
  sg: rework mmap support
  sg: defang allow_dio
  sg: warn v3 write system call users
  sg: add mmap_sz tracking
  sg: remove rcv_done request state
  sg: track lowest inactive and await indexes
  sg: remove unit attention check for device changed
  sg: no_dxfer: move to/from kernel buffers
  sg: add blk_poll support
  sg: bump version to 4.0.12

 drivers/scsi/sg.c      | 5394 +++++++++++++++++++++++++++-------------
 include/scsi/sg.h      |  273 +-
 include/uapi/scsi/sg.h |  375 +++
 3 files changed, 4117 insertions(+), 1925 deletions(-)
 create mode 100644 include/uapi/scsi/sg.h