[PATCH v5 0/4] OPENAT2_REGULAR flag support for openat2

Dorjoy Chowdhury
2026-03-07T14:07:54Z

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.

The following filesystems have been tested by building and booting the kernel
x86 bzImage in a Fedora 43 VM in QEMU. I have tested with OPENAT2_REGULAR that
regular files can be successfully opened and non-regular files (directory, fifo etc)
return -EFTYPE.
- btrfs
- NFS (loopback)
- SMB (loopback)

Changes in v5:
- EFTYPE is already used in BSDs mentioned in commit message
- consistently return -EFTYPE in all 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 | 6 +++
fs/namei.c | 4 ++
fs/nfs/dir.c | 4 ++
fs/open.c | 4 +-
fs/smb/client/dir.c | 14 ++++++-
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, 127 insertions(+), 31 deletions(-)

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2.53.0