[PATCH 00/10] convert the majority of file systems to mmap_prepare

Lorenzo Stoakes
2025-06-16T19:35:11Z

REVIEWER'S NOTES
================

I am basing this on the mm-new branch in Andrew's tree, so let me know if I
should rebase anything here. Given the mm bits touched I did think perhaps
we should take it through the mm tree, however it may be more sensible to
take it through an fs tree - let me know!

Apologies for the noise/churn, but there are some prerequisite steps here
that inform an ordering - "fs: consistently use file_has_valid_mmap_hooks()
helper" being especially critical, and so I put the bulk of the work in the
same series.

Let me know if there's anything I can do to make life easier here.

Thanks!

===============

In commit c84bf6dd2b83 ("mm: introduce new .mmap_prepare() file
callback"), a new hook for mmap was introduced - f_op->mmap_prepare().

This is preferred to the existing f_op->mmap() hook as it does require a
VMA to be established yet, thus allowing the mmap logic to invoke this hook
far, far earlier, prior to inserting a VMA into the virtual address space,
or performing any other heavy handed operations.

This allows for much simpler unwinding on error, and for there to be a
single attempt at merging a VMA rather than having to possibly reattempt a
merge based on potentially altered VMA state.

Far more importantly, it prevents inappropriate manipulation of
incompletely initialised VMA state, which is something that has been the
cause of bugs and complexity in the past.

The intent is to gradually deprecate f_op->mmap, and in that vein this
series coverts the majority of file systems to using f_op->mmap_prepare.

Prerequisite steps are taken - firstly ensuring all checks for mmap
capabilities use the file_has_valid_mmap_hooks() helper rather than
directly checking for f_op->mmap (which is now not a valid check) and
secondly updating daxdev_mapping_supported() to not require a VMA parameter
to allow ext4 and xfs to be converted.

Commit bb666b7c2707 ("mm: add mmap_prepare() compatibility layer for nested
file systems") handles the nasty edge-case of nested file systems like
overlayfs, which introduces a compatibility shim to allow
f_op->mmap_prepare() to be invoked from an f_op->mmap() callback.

This allows for nested filesystems to continue to function correctly with
all file systems regardless of which callback is used. Once we finally
convert all file systems, this shim can be removed.

As a result, ecryptfs, fuse, and overlayfs remain unaltered so they can
nest all other file systems.

We additionally do not update resctl - as this requires an update to
remap_pfn_range() (or an alternative to it) which we defer to a later
series, equally we do not update cramfs which needs a mixed mapping
insertion with the same issue, nor do we update procfs, hugetlbfs, syfs or
kernfs all of which require VMAs for internal state and hooks. We shall
return to all of these later.

Lorenzo Stoakes (10):
mm: rename call_mmap/mmap_prepare to vfs_mmap/mmap_prepare
mm/nommu: use file_has_valid_mmap_hooks() helper
fs: consistently use file_has_valid_mmap_hooks() helper
fs/dax: make it possible to check dev dax support without a VMA
fs/ext4: transition from deprecated .mmap hook to .mmap_prepare
fs/xfs: transition from deprecated .mmap hook to .mmap_prepare
mm/filemap: introduce generic_file_*_mmap_prepare() helpers
fs: convert simple use of generic_file_*_mmap() to .mmap_prepare()
fs: convert most other generic_file_*mmap() users to .mmap_prepare()
fs: replace mmap hook with .mmap_prepare for simple mappings

block/fops.c | 9 +++---
drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 2 +-
fs/9p/vfs_file.c | 13 +++++----
fs/adfs/file.c | 2 +-
fs/affs/file.c | 2 +-
fs/afs/file.c | 11 ++++----
fs/aio.c | 8 +++---
fs/backing-file.c | 4 +--
fs/bcachefs/fs.c | 8 +++---
fs/bfs/file.c | 2 +-
fs/binfmt_elf.c | 4 +--
fs/binfmt_elf_fdpic.c | 2 +-
fs/btrfs/file.c | 7 +++--
fs/ceph/addr.c | 5 ++--
fs/ceph/file.c | 2 +-
fs/ceph/super.h | 2 +-
fs/coda/file.c | 6 ++--
fs/ecryptfs/file.c | 2 +-
fs/erofs/data.c | 16 ++++++-----
fs/exfat/file.c | 7 +++--
fs/ext2/file.c | 12 ++++----
fs/ext4/file.c | 13 +++++----
fs/f2fs/file.c | 7 +++--
fs/fat/file.c | 2 +-
fs/hfs/inode.c | 2 +-
fs/hfsplus/inode.c | 2 +-
fs/hostfs/hostfs_kern.c | 2 +-
fs/hpfs/file.c | 2 +-
fs/jffs2/file.c | 2 +-
fs/jfs/file.c | 2 +-
fs/minix/file.c | 2 +-
fs/nfs/file.c | 13 +++++----
fs/nfs/internal.h | 2 +-
fs/nfs/nfs4file.c | 2 +-
fs/nilfs2/file.c | 8 +++---
fs/ntfs3/file.c | 15 +++++-----
fs/ocfs2/file.c | 4 +--
fs/ocfs2/mmap.c | 5 ++--
fs/ocfs2/mmap.h | 2 +-
fs/omfs/file.c | 2 +-
fs/orangefs/file.c | 10 ++++---
fs/ramfs/file-mmu.c | 2 +-
fs/ramfs/file-nommu.c | 12 ++++----
fs/read_write.c | 2 +-
fs/romfs/mmap-nommu.c | 6 ++--
fs/smb/client/cifsfs.c | 12 ++++----
fs/smb/client/cifsfs.h | 4 +--
fs/smb/client/file.c | 14 ++++++----
fs/ubifs/file.c | 8 +++---
fs/ufs/file.c | 2 +-
fs/vboxsf/file.c | 8 +++---
fs/xfs/xfs_file.c | 15 +++++-----
fs/zonefs/file.c | 10 ++++---
include/linux/dax.h | 16 ++++++-----
include/linux/fs.h | 11 ++++----
ipc/shm.c | 2 +-
mm/filemap.c | 29 ++++++++++++++++++++
mm/internal.h | 2 +-
mm/nommu.c | 2 +-
mm/vma.c | 2 +-
tools/testing/vma/vma_internal.h | 32 ++++++++++++++++++----
61 files changed, 245 insertions(+), 171 deletions(-)

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2.49.0