[PATCH v4 0/3] Convert NFS with fscache to the netfs API

[Dave Wysochanski <dwysocha@redhat.com>]

This patchset converts NFS with fscache non-direct READ IO paths to
use the netfs API with a non-invasive approach.  The existing NFS pgio
layer does not need extensive changes, and is the best way so far I've
found to address Trond's concerns about modifying the IO path [1] as
well as only enabling netfs when fscache is configured and enabled [2].
I have not attempted performance comparisions to address Chuck
Lever's concern [3] because we are not converting the non-fscache
enabled NFS IO paths to netfs.

The main patch to be reviewed is patch #3 which converts nfs_read_folio
and nfs_readahead.

Changes since v3
- PATCH2: Improve #ifdef readability; use VFS_I #define (Jeff Layton)
- PATCH3: Fix Aug 30 kernel test robot <lkp@intel.com> compile warning due
  to unusued 'sreq' variables in fscache.c (test build with W=1)
- PATCH3: Simplify nfs_netfs_init_request (Jeff Layton, Matt Wilcox)

The patches are fairly stable as evidenced with xfstests generic with
various servers: hammerspace w/NFS4.2+fscache,
NetApp(ontap9) NFSv4.1+fscache (other tests in progress)
The known issues are as follows:

No major issues outstanding - the data corruption is unrelated to this
patchset.  The known issues are as follows:

1. Unit test setting rsize < readahead does not properly read from
fscache but re-reads data from the NFS server
* This will be fixed with another linux-cachefs [4] patch to resolve
"Stop read optimisation when folio removed from pagecache"

2. "Cache volume key already in use" after xfstest runs
* xfstests (hammerspace with vers=4.2,fsc) shows the following on the
console after some tests:
"NFS: Cache volume key already in use (nfs,4.1,2,c50,cfe0100a,3,,,8000,100000,100000,bb8,ea60,7530,ea60,1)"
* This may be fixed with another patch [4] that is in progress

3. (RESOLVED) Hang

4. (DEFERRED/UNRELATED) Data corruption seen with unit test where rsize < readahead
* Confirmed unrelated to this patchset
* Seen with vanilla 6.0-rc2 (did not occur on 5.19)
* Not 100% reproducible (maybe 75% of the time)
* NFS protocol version doesn't matter
* First page is always fine, next 3 pages are not
* Garbage data is coming over the wire from the NFS server
because the NFS server file is garbage (the dd of the file from
/tmp to NFS /mnt corrupts it).
 mount -o vers=4.2,fsc,rsize=8192 127.0.0.1:/export /mnt
 dd if=/dev/urandom of=/tmp/integrity-rsize-file1.bin bs=16k count=1
 ./nfs-readahead.sh set /mnt 16384
 dd if=/tmp/integrity-rsize-file1.bin of=/mnt/integrity-rsize-file1.bin bs=16k count=1
 echo 3 > /proc/sys/vm/drop_caches
 md5sum /mnt/integrity-rsize-file1.bin /tmp/integrity-rsize-file1.bin
 md5sums don't match, MD5_NFS = 00eaf1a5bc1b3dfd54711db551619afa != MD5_LOCAL = e8d835c83ba1f1264869dc40673fa20c

5. generic/127 triggers "Subreq overread" warning
* just hit one time; did not stop test
[ 4196.864176] run fstests generic/127 at 2022-08-31 17:29:38
[ 5608.997945] ------------[ cut here ]------------
[ 5609.000476] Subreq overread: R1c85d[0] 73728 > 70073 - 0


The patchset is based on 6.0-rc3 and has been pushed to github at:
https://github.com/DaveWysochanskiRH/kernel/commits/nfs-fscache-netfs

[1] https://lore.kernel.org/linux-nfs/9cfd5bc3cfc6abc2d3316b0387222e708d67f595.camel@hammerspace.com/
[2] https://lore.kernel.org/linux-nfs/da9200f1bded9b8b078a7aef227fd6b92eb028fb.camel@hammerspace.com/
[3] https://marc.info/?l=linux-nfs&m=160597917525083&w=4
[4] https://www.mail-archive.com/linux-cachefs@redhat.com/msg03043.html
[5] https://marc.info/?l=linux-nfs&m=165962662200679&w=4

Dave Wysochanski (3):
  NFS: Rename readpage_async_filler to nfs_pageio_add_page
  NFS: Add support for netfs in struct nfs_inode and Kconfig
  NFS: Convert nfs_read_folio and nfs_readahead to netfs APIs

 fs/nfs/Kconfig           |   1 +
 fs/nfs/delegation.c      |   2 +-
 fs/nfs/dir.c             |   2 +-
 fs/nfs/fscache.c         | 191 ++++++++++++++++++---------------------
 fs/nfs/fscache.h         |  77 ++++++++--------
 fs/nfs/inode.c           |   8 +-
 fs/nfs/internal.h        |  10 +-
 fs/nfs/pagelist.c        |  14 +++
 fs/nfs/pnfs.c            |  12 +--
 fs/nfs/read.c            | 117 ++++++++----------------
 fs/nfs/write.c           |   2 +-
 include/linux/nfs_fs.h   |  19 +---
 include/linux/nfs_page.h |   1 +
 include/linux/nfs_xdr.h  |   1 +
 14 files changed, 210 insertions(+), 247 deletions(-)

-- 
2.31.1