[PATCH v15 00/45] sg: add v4 interface

Douglas Gilbert
2021-01-25T19:12:41Z

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 v1 0/3] io_uring iopoll in scsi
layer". This patchset allows 'iopoll' requests to be issued
without io_uring. iopoll and blk_poll() can be considered
synonymous. One further note, an _async_ interface to blk_poll()
is being proposed.

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 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 (sent to linux-scsi list on 20200301)
- add new patch to ignore the /proc/scsi/sg/allow_dio setting.
Now direct IO will be attempted whenever the SG_FLAG_DIRECT_IO
flag is given
- add new patch to track mmap_sz from previous mmap() call.
Allows catching mmap-ed requests that exceed that value
- change warning about using the v3 interface with the write()
system call from WARN_ONCE() to pr_warn_once()
- remove __KERNEL__ conditionals in include/scsi/sg.h
- change struct sg_fd::start_ns from u64 to ktime_t type
- introduce a new small sg_rq_state_mul2arr array to avoid
a multiplication at runtime in the state machine engine
- tweak mempool introduced in v7 for sense buffers
- rework sg_mk_sgat() to better handle low memory situations;
similar work on sg_remove_sgat_helper()

Changes since v7 (sent to linux-scsi list on 20200227)
- improve direct IO code, remove the SG_FRQ_DIO_IN_USE
sg_request::frq_bm flag as it is no longer needed
- simplify state changing code. Many state changes (rq_st) do not
need changes to the xarray "marks"; only lock those that do
(reviewer queried the locking)
- remove some misplaced likely()/unlikely() macros. They are gathered
together in a separate patch (in a second patchset)
- change a cast that the kbuild robot complained about. It also
flagged a stack size problem in sg_ioctl_common() for reasons not
given nor obvious. That function (and its parents) declare only
simple scalars on the stack.
- add 'Reviewed-by' where appropriate

Changes since v6 (sent to linux-scsi list on 20200112)
- based on Martin Petersen's 5.7/scsi-queue branch in his
linux-scsi repository
- major work on mmap support: when mmap(2) is used the reserve
request scatter gather list is rebuilt to have order=0
elements (i.e. each is PAGE_SIZE bytes).
- address one kbuild robot issue: add include defining size_t
- nearly all patches that have been reviewed have been changed,
usually in minor ways. Those patches have "***" before the
"Reviewed-by" line.

Changes since v5 to v1 in earlier patchsets
- for example: 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 | 5389 +++++++++++++++++++++++++++-------------
include/scsi/sg.h | 273 +-
include/uapi/scsi/sg.h | 375 +++
3 files changed, 4112 insertions(+), 1925 deletions(-)
create mode 100644 include/uapi/scsi/sg.h

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2.25.1