kernel/linux.git/Documentation/filesystems/porting.rst, branch linux-7.1.y

Merge tag 'pull-dcache-busy-wait' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

2026-04-21T14:30:44+00:00

Pull dcache busy loop updates from Al Viro: "Fix livelocks in shrink_dcache_tree() If shrink_dcache_tree() finds a dentry in the middle of being killed by another thread, it has to wait until the victim finishes dying, gets detached from the tree and ceases to pin its parent. The way we used to deal with that amounted to busy-wait; unfortunately, it's not just inefficient but can lead to reliably reproducible hard livelocks. Solved by having shrink_dentry_tree() attach a completion to such dentry, with dentry_unlist() calling complete() on all objects attached to it. With a bit of care it can be done without growing struct dentry or adding overhead in normal case" * tag 'pull-dcache-busy-wait' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: get rid of busy-waiting in shrink_dcache_tree() dcache.c: more idiomatic "positives are not allowed" sanity checks struct dentry: make ->d_u anonymous for_each_alias(): helper macro for iterating through dentries of given inode

for_each_alias(): helper macro for iterating through dentries of given inode

2026-04-02T07:45:02+00:00

Most of the places using d_alias are loops iterating through all aliases for given inode; introduce a helper macro (for_each_alias(dentry, inode)) and convert open-coded instances of such loop to it. They are easier to read that way and it reduces the noise on the next steps. You _must_ hold inode->i_lock over that thing. Signed-off-by: Al Viro

VFS: unexport lock_rename(), lock_rename_child(), unlock_rename()

2026-03-09T08:43:04+00:00

These three function are now only used in namei.c, so they don't need to be exported. Reviewed-by: Jeff Layton Signed-off-by: NeilBrown Link: https://patch.msgid.link/20260224222542.3458677-16-neilb@ownmail.net Signed-off-by: Christian Brauner

VFS: make lookup_one_qstr_excl() static.

2026-03-06T09:24:12+00:00

lookup_one_qstr_excl() is no longer used outside of namei.c, so make it static. Reviewed-by: Jeff Layton Signed-off-by: NeilBrown Link: https://patch.msgid.link/20260224222542.3458677-9-neilb@ownmail.net Signed-off-by: Christian Brauner

Merge tag 'vfs-7.0-rc1.misc.2' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

2026-02-16T21:00:36+00:00

Pull more misc vfs updates from Christian Brauner: "Features: - Optimize close_range() from O(range size) to O(active FDs) by using find_next_bit() on the open_fds bitmap instead of linearly scanning the entire requested range. This is a significant improvement for large-range close operations on sparse file descriptor tables. - Add FS_XFLAG_VERITY file attribute for fs-verity files, retrievable via FS_IOC_FSGETXATTR and file_getattr(). The flag is read-only. Add tracepoints for fs-verity enable and verify operations, replacing the previously removed debug printk's. - Prevent nfsd from exporting special kernel filesystems like pidfs and nsfs. These filesystems have custom ->open() and ->permission() export methods that are designed for open_by_handle_at(2) only and are incompatible with nfsd. Update the exportfs documentation accordingly. Fixes: - Fix KMSAN uninit-value in ovl_fill_real() where strcmp() was used on a non-null-terminated decrypted directory entry name from fscrypt. This triggered on encrypted lower layers when the decrypted name buffer contained uninitialized tail data. The fix also adds VFS-level name_is_dot(), name_is_dotdot(), and name_is_dot_dotdot() helpers, replacing various open-coded "." and ".." checks across the tree. - Fix read-only fsflags not being reset together with xflags in vfs_fileattr_set(). Currently harmless since no read-only xflags overlap with flags, but this would cause inconsistencies for any future shared read-only flag - Return -EREMOTE instead of -ESRCH from PIDFD_GET_INFO when the target process is in a different pid namespace. This lets userspace distinguish "process exited" from "process in another namespace", matching glibc's pidfd_getpid() behavior Cleanups: - Use C-string literals in the Rust seq_file bindings, replacing the kernel::c_str!() macro (available since Rust 1.77) - Fix typo in d_walk_ret enum comment, add porting notes for the readlink_copy() calling convention change" * tag 'vfs-7.0-rc1.misc.2' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: fs: add porting notes about readlink_copy() pidfs: return -EREMOTE when PIDFD_GET_INFO is called on another ns nfsd: do not allow exporting of special kernel filesystems exportfs: clarify the documentation of open()/permission() expotrfs ops fsverity: add tracepoints fs: add FS_XFLAG_VERITY for fs-verity files rust: seq_file: replace `kernel::c_str!` with C-Strings fs: dcache: fix typo in enum d_walk_ret comment ovl: use name_is_dot* helpers in readdir code fs: add helpers name_is_dot{,dot,_dotdot} ovl: Fix uninit-value in ovl_fill_real fs: reset read-only fsflags together with xflags fs/file: optimize close_range() complexity from O(N) to O(Sparse)

Merge tag 'pull-filename' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

2026-02-10T00:58:28+00:00

Pull vfs 'struct filename' updates from Al Viro: "[Mostly] sanitize struct filename handling" * tag 'pull-filename' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (68 commits) sysfs(2): fs_index() argument is _not_ a pathname alpha: switch osf_mount() to strndup_user() ksmbd: use CLASS(filename_kernel) mqueue: switch to CLASS(filename) user_statfs(): switch to CLASS(filename) statx: switch to CLASS(filename_maybe_null) quotactl_block(): switch to CLASS(filename) chroot(2): switch to CLASS(filename) move_mount(2): switch to CLASS(filename_maybe_null) namei.c: switch user pathname imports to CLASS(filename{,_flags}) namei.c: convert getname_kernel() callers to CLASS(filename_kernel) do_f{chmod,chown,access}at(): use CLASS(filename_uflags) do_readlinkat(): switch to CLASS(filename_flags) do_sys_truncate(): switch to CLASS(filename) do_utimes_path(): switch to CLASS(filename_uflags) chdir(2): unspaghettify a bit... do_fchownat(): unspaghettify a bit... fspick(2): use CLASS(filename_flags) name_to_handle_at(): use CLASS(filename_uflags) vfs_open_tree(): use CLASS(filename_uflags) ...

Merge tag 'vfs-7.0-rc1.namespace' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

2026-02-09T22:43:47+00:00

Pull vfs mount updates from Christian Brauner: - statmount: accept fd as a parameter Extend struct mnt_id_req with a file descriptor field and a new STATMOUNT_BY_FD flag. When set, statmount() returns mount information for the mount the fd resides on — including detached mounts (unmounted via umount2(MNT_DETACH)). For detached mounts the STATMOUNT_MNT_POINT and STATMOUNT_MNT_NS_ID mask bits are cleared since neither is meaningful. The capability check is skipped for STATMOUNT_BY_FD since holding an fd already implies prior access to the mount and equivalent information is available through fstatfs() and /proc/pid/mountinfo without privilege. Includes comprehensive selftests covering both attached and detached mount cases. - fs: Remove internal old mount API code (1 patch) Now that every in-tree filesystem has been converted to the new mount API, remove all the legacy shim code in fs_context.c that handled unconverted filesystems. This deletes ~280 lines including legacy_init_fs_context(), the legacy_fs_context struct, and associated wrappers. The mount(2) syscall path for userspace remains untouched. Documentation references to the legacy callbacks are cleaned up. - mount: add OPEN_TREE_NAMESPACE to open_tree() Container runtimes currently use CLONE_NEWNS to copy the caller's entire mount namespace — only to then pivot_root() and recursively unmount everything they just copied. With large mount tables and thousands of parallel container launches this creates significant contention on the namespace semaphore. OPEN_TREE_NAMESPACE copies only the specified mount tree (like OPEN_TREE_CLONE) but returns a mount namespace fd instead of a detached mount fd. The new namespace contains the copied tree mounted on top of a clone of the real rootfs. This functions as a combined unshare(CLONE_NEWNS) + pivot_root() in a single syscall. Works with user namespaces: an unshare(CLONE_NEWUSER) followed by OPEN_TREE_NAMESPACE creates a mount namespace owned by the new user namespace. Mount namespace file mounts are excluded from the copy to prevent cycles. Includes ~1000 lines of selftests" * tag 'vfs-7.0-rc1.namespace' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: selftests/open_tree: add OPEN_TREE_NAMESPACE tests mount: add OPEN_TREE_NAMESPACE fs: Remove internal old mount API code selftests: statmount: tests for STATMOUNT_BY_FD statmount: accept fd as a parameter statmount: permission check should return EPERM

fs: add porting notes about readlink_copy()

2026-02-03T14:17:34+00:00

Calling convention has changed in ea382199071931d1 ("vfs: support caching symlink lengths in inodes") Signed-off-by: Mateusz Guzik Link: https://patch.msgid.link/20260203130032.315177-1-mjguzik@gmail.com Signed-off-by: Christian Brauner

non-consuming variants of do_{unlinkat,rmdir}()

2026-01-16T17:51:50+00:00

similar to previous commit; replacements are filename_{unlinkat,rmdir}() Signed-off-by: Al Viro

non-consuming variant of do_mknodat()

2026-01-16T17:49:26+00:00

similar to previous commit; replacement is filename_mknodat() Signed-off-by: Al Viro