RFC io_uring lseek

From: Hao Xu <[email protected]>

This series adds lseek for io_uring, the motivation to import this syscall is in previous io_uring getdents patchset, we lack a way to rewind the file cursor when it goes to the end of file. Another reason is lseek is a common syscall, it's good for coding consistency when users use io_uring as their main loop.

Patch 1 is code clean for iomap
Patch 2 adds IOMAP_NOWAIT logic for iomap lseek
Patch 3 adds a nowait parameter to for IOMAP_NOWAIT control Patch 4 adds llseek_nowait() for file_operations so that specific
filesystem can implement it for nowait lseek
Patch 5 adds llseek_nowait() implementation for xfs Patch 6 adds a new vfs wrapper for io_uring use
Patch 7 is the main io_uring lseek implementation

Note, this series depends on the previous io_uring getdents series.

This is marked RFC since there is (at least) an issue to be discussed:
The work in this series is mainly to reslove a problem that the current llseek() in struct file_operations doesn't have a place to deliver nowait info, and adding an argument to it results in update for llseek implementation of all filesystems (35 functions), so here I introduce a new llseek_nowait() as a workaround.

For performance, it has about 20%~30% improvement on iops. The test program is just like the one for io_uring getdents, here is the link to it: https://github.com/HowHsu/liburing/blob/llseek/test/lseek.c
- Each test runs about 30000 async requests/sync syscalls
- Each test runs 100 times and get the average value.
- offset is randomly generated value
- the file is a 1M all zero file

[howeyxu@~]$ python3 run_lseek.py
test args:  seek mode:SEEK_SET, offset: 334772
Average of  sync :  0.012300650000000002
Average of  iouring :  0.008528009999999999
30.67%

[howeyxu@~]$ python3 run_lseek.py
test args:  seek mode:SEEK_CUR, offset: 389292
Average of  sync :  0.012736129999999995
Average of  iouring :  0.00928725
27.08%

[howeyxu@~]$ python3 run_lseek.py
test args:  seek mode:SEEK_END, offset: 281141
Average of  sync :  0.01221595
Average of  iouring :  0.008442890000000003
30.89%

[howeyxu@~]$ python3 run_lseek.py
test args:  seek mode:SEEK_DATA, offset: 931103
Average of  sync :  0.015496230000000005
Average of  iouring :  0.012341509999999998
20.36%

[howeyxu@~]$ python3 run_lseek.py
test args:  seek mode:SEEK_HOLE, offset: 430194
Average of  sync :  0.01555663000000001
Average of  iouring :  0.012064940000000003
22.45%

Hao Xu (7):
iomap: merge iomap_seek_hole() and iomap_seek_data()
xfs: add nowait support for xfs_seek_iomap_begin() add nowait parameter for iomap_seek()
add llseek_nowait() for struct file_operations add llseek_nowait support for xfs
add vfs_lseek_nowait()
add lseek for io_uring

 fs/ext4/file.c                |  9 ++---
 fs/gfs2/inode.c               |  4 +--
 fs/iomap/seek.c               | 42 ++++++-----------------
 fs/read_write.c               | 18 ++++++++++
 fs/xfs/xfs_file.c             | 34 ++++++++++++++++---
 fs/xfs/xfs_iomap.c            |  4 ++-
 include/linux/fs.h            |  4 +++
 include/linux/iomap.h         |  6 ++--
 include/uapi/linux/io_uring.h |  1 +
 io_uring/fs.c                 | 63 +++++++++++++++++++++++++++++++++++
 io_uring/fs.h                 |  3 ++
 io_uring/opdef.c              |  8 +++++
 12 files changed, 145 insertions(+), 51 deletions(-)

base-commit: 4a4b046082eca8ae90b654d772fccc30e9f23f4d

2.25.1