[GIT PULL] netfs, afs: Fix write_begin/end

[David Howells]

Hi Linus,

Could you pull this please?  It includes patches to fix netfs_write_begin()
and afs_write_end() in the following ways:

 (1) In netfs_write_begin(), extract the decision about whether to skip a
     page out to its own helper and have that clear around the region to be
     written, but not clear that region.  This requires the filesystem to
     patch it up afterwards if the hole doesn't get completely filled.

 (2) Use offset_in_thp() in (1) rather than manually calculating the offset
     into the page.

 (3) Due to (1), afs_write_end() now needs to handle short data write into
     the page by generic_perform_write().  I've adopted an analogous
     approach to ceph of just returning 0 in this case and letting the
     caller go round again.

It also adds a note that (in the future) the len parameter may extend
beyond the page allocated.  This is because the page allocation is deferred
to write_begin() and that gets to decide what size of THP to allocate.

Thanks,
David

Link: https://lore.kernel.org/r/20210613233345.113565-1-jlayton@xxxxxxxxxx/
Link: https://lore.kernel.org/r/162367681795.460125.11729955608839747375.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v1
Link: https://lore.kernel.org/r/162391823192.1173366.9740514875196345746.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v2
Link: https://lore.kernel.org/r/162429000639.2770648.6368710175435880749.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v3

Changes
=======

ver #3:
   - Drop the bits that make afs take account of len exceeding the end of
     the page in afs_write_begin/end().

ver #2:
   - Removed a var that's no longer used (spotted by the kernel test robot)
   - Removed a forgotten "noinline".

ver #1:
   - Prefixed the Jeff's new helper with "netfs_".
   - Don't call zero_user_segments() for a full-page write.
   - Altered the beyond-last-page check to avoid a DIV.
   - Removed redundant zero-length-file check.
   - Added patches to fix afs.

---
The following changes since commit 009c9aa5be652675a06d5211e1640e02bbb1c33d:

  Linux 5.13-rc6 (2021-06-13 14:43:10 -0700)

are available in the Git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git tags/netfs-fixes-20210621

for you to fetch changes up to 827a746f405d25f79560c7868474aec5aee174e1:

  netfs: fix test for whether we can skip read when writing beyond EOF (2021-06-21 21:24:07 +0100)

----------------------------------------------------------------
netfslib fixes

----------------------------------------------------------------
David Howells (1):
      afs: Fix afs_write_end() to handle short writes

Jeff Layton (1):
      netfs: fix test for whether we can skip read when writing beyond EOF

 fs/afs/write.c         | 11 +++++++++--
 fs/netfs/read_helper.c | 49 ++++++++++++++++++++++++++++++++++++-------------
 2 files changed, 45 insertions(+), 15 deletions(-)