[PATCH v4 0/4] OPENAT2_REGULAR flag support in openat2

Dorjoy Chowdhury
2026-02-21T16:41:06Z

Hi,

I came upon this "Ability to only open regular files" uapi feature suggestion
from https://uapi-group.org/kernel-features/#ability-to-only-open-regular-files
and thought it would be something I could do as a first patch and get to
know the kernel code a bit better.

I only tested this new flag on my local system (fedora btrfs).

Note that I had submitted a v4 previously (that had -EINVAL for the atomic_open
code paths) but did not do a get_maintainers.pl. It didn't get any review and
please ignore that one anyway. In this version, I have tried to properly update
the filesystems that provide atomic_open (fs/ceph, fs/nfs, fs/smb, fs/gfs2,
fs/fuse, fs/vboxsf, fs/9p) for the new OPENAT2_REGULAR flag. Some of them
(fs/fuse, fs/vboxsf, fs/9p) didn't need any changing. As far as I see, most of
the filesystems do finish_no_open for ~O_CREAT and have file->f_mode |= FMODE_CREATED
for the O_CREAT code path which I assume means they always create new file which
is a regular file. OPENAT2_REGULAR | O_DIRECTORY returns -EINVAL (instead of working
if path is either a directory or regular file) as it was easier to reason about when
making changes in all the filesystems.

Changes in v4:
- changed O_REGULAR to OPENAT2_REGULAR
- OPENAT2_REGULAR does not affect O_PATH
- atomic_open codepaths updated to work properly for OPENAT2_REGULAR
- commit message includes the uapi-group URL
- v3 is at: https://lore.kernel.org/linux-fsdevel/20260127180109.66691-1-dorjoychy111@gmail.com/T/

Changes in v3:
- included motivation about O_REGULAR flag in commit message e.g., programs not wanting to be tricked into opening device nodes
- fixed commit message wrongly referencing ENOTREGULAR instead of ENOTREG
- fixed the O_REGULAR flag in arch/parisc/include/uapi/asm/fcntl.h from 060000000 to 0100000000
- added 2 commits converting arch/{mips,sparc}/include/uapi/asm/fcntl.h O_* macros from hex to octal
- v2 is at: https://lore.kernel.org/linux-fsdevel/20260126154156.55723-1-dorjoychy111@gmail.com/T/

Changes in v2:
- rename ENOTREGULAR to ENOTREG
- define ENOTREG in uapi/asm-generic/errno.h (instead of errno-base.h) and in arch/*/include/uapi/asm/errno.h files
- override O_REGULAR in arch/{alpha,sparc,parisc}/include/uapi/asm/fcntl.h due to clash with include/uapi/asm-generic/fcntl.h
- I have kept the kselftest but now that O_REGULAR and ENOTREG can have different value on different architectures I am not sure if it's right
- v1 is at: https://lore.kernel.org/linux-fsdevel/20260125141518.59493-1-dorjoychy111@gmail.com/T/

Thanks.

Regards,
Dorjoy

Dorjoy Chowdhury (4):
openat2: new OPENAT2_REGULAR flag support
kselftest/openat2: test for OPENAT2_REGULAR flag
sparc/fcntl.h: convert O_* flag macros from hex to octal
mips/fcntl.h: convert O_* flag macros from hex to octal

arch/alpha/include/uapi/asm/errno.h | 2 +
arch/alpha/include/uapi/asm/fcntl.h | 1 +
arch/mips/include/uapi/asm/errno.h | 2 +
arch/mips/include/uapi/asm/fcntl.h | 22 +++++------
arch/parisc/include/uapi/asm/errno.h | 2 +
arch/parisc/include/uapi/asm/fcntl.h | 1 +
arch/sparc/include/uapi/asm/errno.h | 2 +
arch/sparc/include/uapi/asm/fcntl.h | 35 +++++++++---------
fs/ceph/file.c | 4 ++
fs/gfs2/inode.c | 2 +
fs/namei.c | 4 ++
fs/nfs/dir.c | 4 +-
fs/open.c | 4 +-
fs/smb/client/dir.c | 11 +++++-
include/linux/fcntl.h | 2 +
include/uapi/asm-generic/errno.h | 2 +
include/uapi/asm-generic/fcntl.h | 4 ++
tools/arch/alpha/include/uapi/asm/errno.h | 2 +
tools/arch/mips/include/uapi/asm/errno.h | 2 +
tools/arch/parisc/include/uapi/asm/errno.h | 2 +
tools/arch/sparc/include/uapi/asm/errno.h | 2 +
tools/include/uapi/asm-generic/errno.h | 2 +
.../testing/selftests/openat2/openat2_test.c | 37 ++++++++++++++++++-
23 files changed, 119 insertions(+), 32 deletions(-)

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2.53.0