Pull netfs updates from Christian Brauner:
 "This extends the netfs helper library that network filesystems can use
  to replace their own implementations. Both afs and 9p are ported. cifs
  is ready as well but the patches are way bigger and will be routed
  separately once this is merged. That will remove lots of code as well.

  The overal goal is to get high-level I/O and knowledge of the page
  cache and ouf of the filesystem drivers. This includes knowledge about
  the existence of pages and folios

  The pull request converts afs and 9p. This removes about 800 lines of
  code from afs and 300 from 9p. For 9p it is now possible to do writes
  in larger than a page chunks. Additionally, multipage folio support
  can be turned on for 9p. Separate patches exist for cifs removing
  another 2000+ lines. I've included detailed information in the
  individual pulls I took.

  Summary:

   - Add NFS-style (and Ceph-style) locking around DIO vs buffered I/O
     calls to prevent these from happening at the same time.

   - Support for direct and unbuffered I/O.

   - Support for write-through caching in the page cache.

   - O_*SYNC and RWF_*SYNC writes use write-through rather than writing
     to the page cache and then flushing afterwards.

   - Support for write-streaming.

   - Support for write grouping.

   - Skip reads for which the server could only return zeros or EOF.

   - The fscache module is now part of the netfs library and the
     corresponding maintainer entry is updated.

   - Some helpers from the fscache subsystem are renamed to mark them as
     belonging to the netfs library.

   - Follow-up fixes for the netfs library.

   - Follow-up fixes for the 9p conversion"

* tag 'vfs-6.8.netfs' of gitolite.kernel.org:pub/scm/linux/kernel/git/vfs/vfs: (50 commits)
  netfs: Fix wrong #ifdef hiding wait
  cachefiles: Fix signed/unsigned mixup
  netfs: Fix the loop that unmarks folios after writing to the cache
  netfs: Fix interaction between write-streaming and cachefiles culling
  netfs: Count DIO writes
  netfs: Mark netfs_unbuffered_write_iter_locked() static
  netfs: Fix proc/fs/fscache symlink to point to "netfs" not "../netfs"
  netfs: Rearrange netfs_io_subrequest to put request pointer first
  9p: Use length of data written to the server in preference to error
  9p: Do a couple of cleanups
  9p: Fix initialisation of netfs_inode for 9p
  cachefiles: Fix __cachefiles_prepare_write()
  9p: Use netfslib read/write_iter
  afs: Use the netfs write helpers
  netfs: Export the netfs_sreq tracepoint
  netfs: Optimise away reads above the point at which there can be no data
  netfs: Implement a write-through caching option
  netfs: Provide a launder_folio implementation
  netfs: Provide a writepages implementation
  netfs, cachefiles: Pass upper bound length to allow expansion
  ...

Pull afs updates from David Howells:
 "The majority of the patches are aimed at fixing and improving the AFS
  filesystem's rotation over server IP addresses, but there are also
  some fixes from Oleg Nesterov for the use of read_seqbegin_or_lock().

   - Fix fileserver probe handling so that the next round of probes
     doesn't break ongoing server/address rotation by clearing all the
     probe result tracking. This could occasionally cause the rotation
     algorithm to drop straight through, give a 'successful' result
     without actually emitting any RPC calls, leaving the reply buffer
     in an undefined state.

     Instead, detach the probe results into a separate struct and
     allocate a new one each time we start probing and update the
     pointer to it. Probes are also sent in order of address preference
     to try and improve the chance that the preferred one will complete
     first.

   - Fix server rotation so that it uses configurable address
     preferences across on the probes that have completed so far than
     ranking them by RTT as the latter doesn't necessarily give the best
     route. The preference list can be altered by writing into
     /proc/net/afs/addr_prefs.

   - Fix the handling of Read-Only (and Backup) volume callbacks as
     there is one per volume, not one per file, so if someone performs a
     command that, say, offlines the volume but doesn't change it, when
     it comes back online we don't spam the server with a status fetch
     for every vnode we're using. Instead, check the Creation timestamp
     in the VolSync record when prompted by a callback break.

   - Handle volume regression (ie. a RW volume being restored from a
     backup) by scrubbing all cache data for that volume. This is
     detected from the VolSync creation timestamp.

   - Adjust abort handling and abort -> error mapping to match better
     with what other AFS clients do.

   - Fix offline and busy volume state handling as they only apply to
     individual server instances and not entire volumes and the rotation
     algorithm should go and look at other servers if available. Also
     make it sleep briefly before each retry if all the volume instances
     are unavailable"

* tag 'afs-fix-rotation-20240105' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs: (40 commits)
  afs: trace: Log afs_make_call(), including server address
  afs: Fix offline and busy message emission
  afs: Fix fileserver rotation
  afs: Overhaul invalidation handling to better support RO volumes
  afs: Parse the VolSync record in the reply of a number of RPC ops
  afs: Don't leave DONTUSE/NEWREPSITE servers out of server list
  afs: Fix comment in afs_do_lookup()
  afs: Apply server breaks to mmap'd files in the call processor
  afs: Move the vnode/volume validity checking code into its own file
  afs: Defer volume record destruction to a workqueue
  afs: Make it possible to find the volumes that are using a server
  afs: Combine the endpoint state bools into a bitmask
  afs: Keep a record of the current fileserver endpoint state
  afs: Dispatch vlserver probes in priority order
  afs: Dispatch fileserver probes in priority order
  afs: Mark address lists with configured priorities
  afs: Provide a way to configure address priorities
  afs: Remove the unimplemented afs_cmp_addr_list()
  afs: Add some more info to /proc/net/afs/servers
  rxrpc: Create a procfile to display outstanding client conn bundles
  ...

Make afs use the netfs write helpers.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org

Wrap most op->error accesses with inline funcs which will make it easier
for a subsequent patch to replace op->error with something else.  Two
functions are added to this end:

 (1) afs_op_error() - Get the error code.

 (2) afs_op_set_error() - Set the error code.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org

AFS currently uses folio->private to store the range of bytes within a
folio that have been modified - the idea being that if we have, say, a 2MiB
folio and someone writes a single byte, we only have to write back that
single page and not the whole 2MiB folio - thereby saving on network
bandwidth.

Remove this, at least for now, and accept the extra network load (which
doesn't matter in the common case of writing a whole file at a time from
beginning to end).

This makes folio->private available for netfslib to use.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org

Move the resource pinning-for-writeback from fscache code to netfslib code.
This is used to keep a cache backing object pinned whilst we have dirty
pages on the netfs inode in the pagecache such that VM writeback will be
able to reach it.

Whilst we're at it, switch the parameters of netfs_unpin_writeback() to
match ->write_inode() so that it can be used for that directly.

Note that this mechanism could be more generically useful than that for
network filesystems.  Quite often they have to keep around other resources
(e.g. authentication tokens or network connections) until the writeback is
complete.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org

There were already assertions that we were not passing a tail page to
error_remove_page(), so make the compiler enforce that by converting
everything to pass and use a folio.

Link: https://lkml.kernel.org/r/20231117161447.2461643-7-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

In preparation for removing the return value entirely, stop testing it
in afs.

Link: https://lkml.kernel.org/r/20231108204605.745109-3-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Steve French <sfrench@samba.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Convert to using the new inode timestamp accessor functions.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://lore.kernel.org/r/20231004185347.80880-16-jlayton@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

When an AFS FS.StoreData RPC call is made, amongst other things it is
given the resultant file size to be.  On the server, this is processed
by truncating the file to new size and then writing the data.

Now, kafs has a lock (vnode->io_lock) that serves to serialise
operations against a specific vnode (ie.  inode), but the parameters for
the op are set before the lock is taken.  This allows two writebacks
(say sync and kswapd) to race - and if writes are ongoing the writeback
for a later write could occur before the writeback for an earlier one if
the latter gets interrupted.

Note that afs_writepages() cannot take i_mutex and only takes a shared
lock on vnode->validate_lock.

Also note that the server does the truncation and the write inside a
lock, so there's no problem at that end.

Fix this by moving the calculation for the proposed new i_size inside
the vnode->io_lock.  Also reset the iterator (which we might have read
from) and update the mtime setting there.

Fixes: bd80d8a80e12 ("afs: Use ITER_XARRAY for writing")
Reported-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeffrey Altman <jaltman@auristor.com>
Reviewed-by: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/3526895.1687960024@warthog.procyon.org.uk/
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>