Pull overlayfs update from Miklos Szeredi:

 - Fix a regression in getting the path of an open file (e.g. in
   /proc/PID/maps) for a nested overlayfs setup (André Almeida)

 - Support data-only layers and verity in a user namespace (unprivileged
   composefs use case)

 - Fix a gcc warning (Kees)

 - Cleanups

* tag 'ovl-update-v2-6.16' of git://git.kernel.org/pub/scm/linux/kernel/git/overlayfs/vfs:
  ovl: Annotate struct ovl_entry with __counted_by()
  ovl: Replace offsetof() with struct_size() in ovl_stack_free()
  ovl: Replace offsetof() with struct_size() in ovl_cache_entry_new()
  ovl: Check for NULL d_inode() in ovl_dentry_upper()
  ovl: Use str_on_off() helper in ovl_show_options()
  ovl: don't require "metacopy=on" for "verity"
  ovl: relax redirect/metacopy requirements for lower -> data redirect
  ovl: make redirect/metacopy rejection consistent
  ovl: Fix nested backing file paths

Pull misc vfs updates from Christian Brauner:
 "This contains the usual selections of misc updates for this cycle.

  Features:

   - Use folios for symlinks in the page cache

     FUSE already uses folios for its symlinks. Mirror that conversion
     in the generic code and the NFS code. That lets us get rid of a few
     folio->page->folio conversions in this path, and some of the few
     remaining users of read_cache_page() / read_mapping_page()

   - Try and make a few filesystem operations killable on the VFS
     inode->i_mutex level

   - Add sysctl vfs_cache_pressure_denom for bulk file operations

     Some workloads need to preserve more dentries than we currently
     allow through out sysctl interface

     A HDFS servers with 12 HDDs per server, on a HDFS datanode startup
     involves scanning all files and caching their metadata (including
     dentries and inodes) in memory. Each HDD contains approximately 2
     million files, resulting in a total of ~20 million cached dentries
     after initialization

     To minimize dentry reclamation, they set vfs_cache_pressure to 1.
     Despite this configuration, memory pressure conditions can still
     trigger reclamation of up to 50% of cached dentries, reducing the
     cache from 20 million to approximately 10 million entries. During
     the subsequent cache rebuild period, any HDFS datanode restart
     operation incurs substantial latency penalties until full cache
     recovery completes

     To maintain service stability, more dentries need to be preserved
     during memory reclamation. The current minimum reclaim ratio (1/100
     of total dentries) remains too aggressive for such workload. This
     patch introduces vfs_cache_pressure_denom for more granular cache
     pressure control

     The configuration [vfs_cache_pressure=1,
     vfs_cache_pressure_denom=10000] effectively maintains the full 20
     million dentry cache under memory pressure, preventing datanode
     restart performance degradation

   - Avoid some jumps in inode_permission() using likely()/unlikely()

   - Avid a memory access which is most likely a cache miss when
     descending into devcgroup_inode_permission()

   - Add fastpath predicts for stat() and fdput()

   - Anonymous inodes currently don't come with a proper mode causing
     issues in the kernel when we want to add useful VFS debug assert.
     Fix that by giving them a proper mode and masking it off when we
     report it to userspace which relies on them not having any mode

   - Anonymous inodes currently allow to change inode attributes because
     the VFS falls back to simple_setattr() if i_op->setattr isn't
     implemented. This means the ownership and mode for every single
     user of anon_inode_inode can be changed. Block that as it's either
     useless or actively harmful. If specific ownership is needed the
     respective subsystem should allocate anonymous inodes from their
     own private superblock

   - Raise SB_I_NODEV and SB_I_NOEXEC on the anonymous inode superblock

   - Add proper tests for anonymous inode behavior

   - Make it easy to detect proper anonymous inodes and to ensure that
     we can detect them in codepaths such as readahead()

  Cleanups:

   - Port pidfs to the new anon_inode_{g,s}etattr() helpers

   - Try to remove the uselib() system call

   - Add unlikely branch hint return path for poll

   - Add unlikely branch hint on return path for core_sys_select

   - Don't allow signals to interrupt getdents copying for fuse

   - Provide a size hint to dir_context for during readdir()

   - Use writeback_iter directly in mpage_writepages

   - Update compression and mtime descriptions in initramfs
     documentation

   - Update main netfs API document

   - Remove useless plus one in super_cache_scan()

   - Remove unnecessary NULL-check guards during setns()

   - Add separate separate {get,put}_cgroup_ns no-op cases

  Fixes:

   - Fix typo in root= kernel parameter description

   - Use KERN_INFO for infof()|info_plog()|infofc()

   - Correct comments of fs_validate_description()

   - Mark an unlikely if condition with unlikely() in
     vfs_parse_monolithic_sep()

   - Delete macro fsparam_u32hex()

   - Remove unused and problematic validate_constant_table()

   - Fix potential unsigned integer underflow in fs_name()

   - Make file-nr output the total allocated file handles"

* tag 'vfs-6.16-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (43 commits)
  fs: Pass a folio to page_put_link()
  nfs: Use a folio in nfs_get_link()
  fs: Convert __page_get_link() to use a folio
  fs/read_write: make default_llseek() killable
  fs/open: make do_truncate() killable
  fs/open: make chmod_common() and chown_common() killable
  include/linux/fs.h: add inode_lock_killable()
  readdir: supply dir_context.count as readdir buffer size hint
  vfs: Add sysctl vfs_cache_pressure_denom for bulk file operations
  fuse: don't allow signals to interrupt getdents copying
  Documentation: fix typo in root= kernel parameter description
  include/cgroup: separate {get,put}_cgroup_ns no-op case
  kernel/nsproxy: remove unnecessary guards
  fs: use writeback_iter directly in mpage_writepages
  fs: remove useless plus one in super_cache_scan()
  fs: add S_ANON_INODE
  fs: remove uselib() system call
  device_cgroup: avoid access to ->i_rdev in the common case in devcgroup_inode_permission()
  fs/fs_parse: Remove unused and problematic validate_constant_table()
  fs: touch up predicts in inode_permission()
  ...

This is a preparation for large readdir buffers in fuse.

Simply setting the fuse buffer size to the userspace buffer size should
work, the record sizes are similar (fuse's is slightly larger than libc's,
so no overflow should ever happen).

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Jaco Kroon <jaco@uls.co.za>
Link: https://lore.kernel.org/20250513151012.1476536-1-mszeredi@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

Compared to offsetof(), struct_size() provides additional compile-time
checks for structs with flexible arrays (e.g., __must_be_array()).

No functional changes intended.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

The family of functions:
  lookup_one()
  lookup_one_unlocked()
  lookup_one_positive_unlocked()

appear designed to be used by external clients of the filesystem rather
than by filesystems acting on themselves as the lookup_one_len family
are used.

They are used by:
   btrfs/ioctl - which is a user-space interface rather than an internal
     activity
   exportfs - i.e. from nfsd or the open_by_handle_at interface
   overlayfs - at access the underlying filesystems
   smb/server - for file service

They should be used by nfsd (more than just the exportfs path) and
cachefs but aren't.

It would help if the documentation didn't claim they should "not be
called by generic code".

Also the path component name is passed as "name" and "len" which are
(confusingly?) separate by the "base".  In some cases the len in simply
"strlen" and so passing a qstr using QSTR() would make the calling
clearer.
Other callers do pass separate name and len which are stored in a
struct.  Sometimes these are already stored in a qstr, other times it
easily could be.

So this patch changes these three functions to receive a 'struct qstr *',
and improves the documentation.

QSTR_LEN() is added to make it easy to pass a QSTR containing a known
len.

[brauner@kernel.org: take a struct qstr pointer]
Signed-off-by: NeilBrown <neil@brown.name>
Link: https://lore.kernel.org/r/20250319031545.2999807-2-neil@brown.name
Signed-off-by: Christian Brauner <brauner@kernel.org>

Introduce ovl_revert_creds() wrapper of revert_creds() to
match callers of ovl_override_creds().

Suggested-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>

An opaque directory cannot have xwhiteouts, so instead of marking an
xwhiteouts directory with a new xattr, overload overlay.opaque xattr
for marking both opaque dir ('y') and xwhiteouts dir ('x').

This is more efficient as the overlay.opaque xattr is checked during
lookup of directory anyway.

This also prevents unnecessary checking the xattr when reading a
directory without xwhiteouts, i.e. most of the time.

Note that the xwhiteouts marker is not checked on the upper layer and
on the last layer in lowerstack, where xwhiteouts are not expected.

Fixes: bc8df7a3dc03 ("ovl: Add an alternative type of whiteout")
Cc: <stable@vger.kernel.org> # v6.7
Reviewed-by: Alexander Larsson <alexl@redhat.com>
Tested-by: Alexander Larsson <alexl@redhat.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>

When the index feature is disabled, ofs->indexdir is NULL.
When the index feature is enabled, ofs->indexdir has the same value as
ofs->workdir and takes an extra reference.

This makes the code harder to understand when it is not always clear
that ofs->indexdir in one function is the same dentry as ofs->workdir
in another function.

Remove this redundancy, by referencing ofs->workdir directly in index
helpers and by using the ovl_indexdir() accessor in generic code.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>

An xattr whiteout (called "xwhiteout" in the code) is a reguar file of
zero size with the "overlay.whiteout" xattr set. A file like this in a
directory with the "overlay.whiteouts" xattrs set will be treated the
same way as a regular whiteout.

The "overlay.whiteouts" directory xattr is used in order to
efficiently handle overlay checks in readdir(), as we only need to
checks xattrs in affected directories.

The advantage of this kind of whiteout is that they can be escaped
using the standard overlay xattr escaping mechanism. So, a file with a
"overlay.overlay.whiteout" xattr would be unescaped to
"overlay.whiteout", which could then be consumed by another overlayfs
as a whiteout.

Overlayfs itself doesn't create whiteouts like this, but a userspace
mechanism could use this alternative mechanism to convert images that
may contain whiteouts to be used with overlayfs.

To work as a whiteout for both regular overlayfs mounts as well as
userxattr mounts both the "user.overlay.whiteout*" and the
"trusted.overlay.whiteout*" xattrs will need to be created.

Signed-off-by: Alexander Larsson <alexl@redhat.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>

All users now just use '->iterate_shared()', which only takes the
directory inode lock for reading.

Filesystems that never got convered to shared mode now instead use a
wrapper that drops the lock, re-takes it in write mode, calls the old
function, and then downgrades the lock back to read mode.

This way the VFS layer and other callers no longer need to care about
filesystems that never got converted to the modern era.

The filesystems that use the new wrapper are ceph, coda, exfat, jfs,
ntfs, ocfs2, overlayfs, and vboxsf.

Honestly, several of them look like they really could just iterate their
directories in shared mode and skip the wrapper entirely, but the point
of this change is to not change semantics or fix filesystems that
haven't been fixed in the last 7+ years, but to finally get rid of the
dual iterators.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>