On Sun, 2026-03-01 at 20:16 +0600, Dorjoy Chowdhury wrote: > On Sun, Mar 1, 2026 at 6:44 PM Jeff Layton <[email protected]> wrote: > > > > On Sat, 2026-02-21 at 20:45 +0600, Dorjoy Chowdhury wrote: > > > This flag indicates the path should be opened if it's a regular file. > > > This is useful to write secure programs that want to avoid being > > > tricked into opening device nodes with special semantics while thinking > > > they operate on regular files. This is a requested feature from the > > > uapi-group[1]. > > > > > > A corresponding error code EFTYPE has been introduced. For example, if > > > openat2 is called on path /dev/null with OPENAT2_REGULAR in the flag > > > param, it will return -EFTYPE. > > > > > > When used in combination with O_CREAT, either the regular file is > > > created, or if the path already exists, it is opened if it's a regular > > > file. Otherwise, -EFTYPE is returned. > > > > > > > It would be good to mention that EFTYPE has precedent in BSD/Darwin. > > When an error code is already supported in another UNIX-y OS, then it > > bolsters the case for adding it here. > > > > Good suggestion. Yes, I can include this information in the commit > message during the next posting. > > > Your cover letter mentions that you only tested this on btrfs. At the > > very least, you should test NFS and SMB. It should be fairly easy to > > set up mounts over loopback for those cases. > > > > I used virtme-ng (which I think reuses the host's filesystem) to run > the compiled bzImage and ran the openat2 kselftests there to verify > it's working. Is there a similar way I can test NFS/SMB by adding > kselftests? Or would I need to setup NFS/SMB inside a full VM distro > with a modified kernel to test this? I would appreciate any suggestion > on this. >
I imagine virtme would need some configuration to set up for nfs or cifs, but maybe it's possible. I mostly use kdevops for this sort of testing. > > There are some places where it doesn't seem like -EFTYPE will be > > returned. It looks like it can send back -EISDIR and -ENOTDIR in some > > cases as well. With a new API like this, I think we ought to strive for > > consistency. > > > > Good point. There was a comment in a previous posting of this patch > series "The most useful behavior would indicate what was found (e.g., > a pipe)." > (ref: > https://lore.kernel.org/linux-fsdevel/vhq3osjqs3nn764wrp2lxp66b4dxpb3n5x3dijhe2yr53qfgy3@tfswbjskc3y6/ > ) > So I thought maybe it would be useful to return -EISDIR where it was > already doing that. But it is a good point about consistency that we > won't be doing this for other different types so I guess it's better > to return -EFTYPE for all the cases anyway as you mention. Any > thoughts? > There is a case to be made for either. The big question is whether you can consistently return the same error codes in the same situations. For instance, you can return -EISDIR on NFS when the target is a directory, but can you do the same on btrfs or ceph? If not, then we have a situation where we have to deal with the possibility of two different error codes. In general, I think returning EFTYPE for everything is simplest and therefore best. Sure, EISDIR tells you a bit more about the target, but that info is probably not that helpful if you were expecting it to be a regular file. > > > Should this API return -EFTYPE for all cases where it's not S_IFREG? If > > not, then what other errors are allowed? Bear in mind that you'll need > > to document this in the manpages too. > > > > Are the manpages in the kernel git repository or in a separate > repository? Do I make separate patch series for that? Sorry I don't > know about this in detail. > Separate repo and mailing list: https://www.kernel.org/doc/man-pages/ ...come to think of it, you should also cc the linux-api mailing list when you send the next version: https://www.kernel.org/doc/man-pages/linux-api-ml.html This one is fairly straightforward, but once a new API is in a released kernel, it's hard to change things, so we'll want to make sure we get this right. I should also ask you about testcases here. You should add some tests to fstests for O_REGULAR if you haven't already: https://www.kernel.org/doc/man-pages/linux-api-ml.html > > > When OPENAT2_REGULAR is combined with O_DIRECTORY, -EINVAL is returned > > > as it doesn't make sense to open a path that is both a directory and a > > > regular file. > > > > > > [1]: > > > https://uapi-group.org/kernel-features/#ability-to-only-open-regular-files > > > > > > Signed-off-by: Dorjoy Chowdhury <[email protected]> > > > --- > > > 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/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 | 1 + > > > 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 ++ > > > 21 files changed, 55 insertions(+), 3 deletions(-) > > > > > > diff --git a/arch/alpha/include/uapi/asm/errno.h > > > b/arch/alpha/include/uapi/asm/errno.h > > > index 6791f6508632..1a99f38813c7 100644 > > > --- a/arch/alpha/include/uapi/asm/errno.h > > > +++ b/arch/alpha/include/uapi/asm/errno.h > > > @@ -127,4 +127,6 @@ > > > > > > #define EHWPOISON 139 /* Memory page has hardware error */ > > > > > > +#define EFTYPE 140 /* Wrong file type for the intended > > > operation */ > > > + > > > #endif > > > diff --git a/arch/alpha/include/uapi/asm/fcntl.h > > > b/arch/alpha/include/uapi/asm/fcntl.h > > > index 50bdc8e8a271..fe488bf7c18e 100644 > > > --- a/arch/alpha/include/uapi/asm/fcntl.h > > > +++ b/arch/alpha/include/uapi/asm/fcntl.h > > > @@ -34,6 +34,7 @@ > > > > > > #define O_PATH 040000000 > > > #define __O_TMPFILE 0100000000 > > > +#define OPENAT2_REGULAR 0200000000 > > > > > > #define F_GETLK 7 > > > #define F_SETLK 8 > > > diff --git a/arch/mips/include/uapi/asm/errno.h > > > b/arch/mips/include/uapi/asm/errno.h > > > index c01ed91b1ef4..1835a50b69ce 100644 > > > --- a/arch/mips/include/uapi/asm/errno.h > > > +++ b/arch/mips/include/uapi/asm/errno.h > > > @@ -126,6 +126,8 @@ > > > > > > #define EHWPOISON 168 /* Memory page has hardware error */ > > > > > > +#define EFTYPE 169 /* Wrong file type for the intended > > > operation */ > > > + > > > #define EDQUOT 1133 /* Quota exceeded */ > > > > > > > > > diff --git a/arch/parisc/include/uapi/asm/errno.h > > > b/arch/parisc/include/uapi/asm/errno.h > > > index 8cbc07c1903e..93194fbb0a80 100644 > > > --- a/arch/parisc/include/uapi/asm/errno.h > > > +++ b/arch/parisc/include/uapi/asm/errno.h > > > @@ -124,4 +124,6 @@ > > > > > > #define EHWPOISON 257 /* Memory page has hardware error */ > > > > > > +#define EFTYPE 258 /* Wrong file type for the intended > > > operation */ > > > + > > > #endif > > > diff --git a/arch/parisc/include/uapi/asm/fcntl.h > > > b/arch/parisc/include/uapi/asm/fcntl.h > > > index 03dee816cb13..d46812f2f0f4 100644 > > > --- a/arch/parisc/include/uapi/asm/fcntl.h > > > +++ b/arch/parisc/include/uapi/asm/fcntl.h > > > @@ -19,6 +19,7 @@ > > > > > > #define O_PATH 020000000 > > > #define __O_TMPFILE 040000000 > > > +#define OPENAT2_REGULAR 0100000000 > > > > > > #define F_GETLK64 8 > > > #define F_SETLK64 9 > > > diff --git a/arch/sparc/include/uapi/asm/errno.h > > > b/arch/sparc/include/uapi/asm/errno.h > > > index 4a41e7835fd5..71940ec9130b 100644 > > > --- a/arch/sparc/include/uapi/asm/errno.h > > > +++ b/arch/sparc/include/uapi/asm/errno.h > > > @@ -117,4 +117,6 @@ > > > > > > #define EHWPOISON 135 /* Memory page has hardware error */ > > > > > > +#define EFTYPE 136 /* Wrong file type for the intended > > > operation */ > > > + > > > #endif > > > diff --git a/arch/sparc/include/uapi/asm/fcntl.h > > > b/arch/sparc/include/uapi/asm/fcntl.h > > > index 67dae75e5274..bb6e9fa94bc9 100644 > > > --- a/arch/sparc/include/uapi/asm/fcntl.h > > > +++ b/arch/sparc/include/uapi/asm/fcntl.h > > > @@ -37,6 +37,7 @@ > > > > > > #define O_PATH 0x1000000 > > > #define __O_TMPFILE 0x2000000 > > > +#define OPENAT2_REGULAR 0x4000000 > > > > > > #define F_GETOWN 5 /* for sockets. */ > > > #define F_SETOWN 6 /* for sockets. */ > > > diff --git a/fs/ceph/file.c b/fs/ceph/file.c > > > index 31b691b2aea2..0a4220f72ada 100644 > > > --- a/fs/ceph/file.c > > > +++ b/fs/ceph/file.c > > > @@ -977,6 +977,10 @@ int ceph_atomic_open(struct inode *dir, struct > > > dentry *dentry, > > > ceph_init_inode_acls(newino, &as_ctx); > > > file->f_mode |= FMODE_CREATED; > > > } > > > + if ((flags & OPENAT2_REGULAR) && !d_is_reg(dentry)) { > > > + err = -EFTYPE; > > > + goto out_req; > > > + } > > > err = finish_open(file, dentry, ceph_open); > > > } > > > out_req: > > > diff --git a/fs/gfs2/inode.c b/fs/gfs2/inode.c > > > index 8344040ecaf7..0dc3e4240d9e 100644 > > > --- a/fs/gfs2/inode.c > > > +++ b/fs/gfs2/inode.c > > > @@ -749,6 +749,8 @@ static int gfs2_create_inode(struct inode *dir, > > > struct dentry *dentry, > > > if (file) { > > > if (S_ISREG(inode->i_mode)) > > > error = finish_open(file, dentry, > > > gfs2_open_common); > > > + else if (file->f_flags & OPENAT2_REGULAR) > > > + error = -EFTYPE; > > > else > > > error = finish_no_open(file, NULL); > > > } > > > diff --git a/fs/namei.c b/fs/namei.c > > > index 5fe6cac48df8..aa5fb2672881 100644 > > > --- a/fs/namei.c > > > +++ b/fs/namei.c > > > @@ -4651,6 +4651,10 @@ static int do_open(struct nameidata *nd, > > > if (unlikely(error)) > > > return error; > > > } > > > + > > > + if ((open_flag & OPENAT2_REGULAR) && !d_is_reg(nd->path.dentry)) > > > + return -EFTYPE; > > > + > > > if ((nd->flags & LOOKUP_DIRECTORY) && > > > !d_can_lookup(nd->path.dentry)) > > > return -ENOTDIR; > > > > > > diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c > > > index b3f5c9461204..ef61db67d06e 100644 > > > --- a/fs/nfs/dir.c > > > +++ b/fs/nfs/dir.c > > > @@ -2195,7 +2195,9 @@ int nfs_atomic_open(struct inode *dir, struct > > > dentry *dentry, > > > break; > > > case -EISDIR: > > > case -ENOTDIR: > > > - goto no_open; > > > + if (!(open_flags & OPENAT2_REGULAR)) > > > + goto no_open; > > > + break; > > > > Shouldn't this also set the error to -EFTYPE? > > > > > case -ELOOP: > > > if (!(open_flags & O_NOFOLLOW)) > > > goto no_open; > > > diff --git a/fs/open.c b/fs/open.c > > > index 91f1139591ab..1524f52a1773 100644 > > > --- a/fs/open.c > > > +++ b/fs/open.c > > > @@ -1198,7 +1198,7 @@ inline int build_open_flags(const struct open_how > > > *how, struct open_flags *op) > > > * values before calling build_open_flags(), but openat2(2) checks > > > all > > > * of its arguments. > > > */ > > > - if (flags & ~VALID_OPEN_FLAGS) > > > + if (flags & ~VALID_OPENAT2_FLAGS) > > > return -EINVAL; > > > if (how->resolve & ~VALID_RESOLVE_FLAGS) > > > return -EINVAL; > > > @@ -1237,6 +1237,8 @@ inline int build_open_flags(const struct open_how > > > *how, struct open_flags *op) > > > return -EINVAL; > > > if (!(acc_mode & MAY_WRITE)) > > > return -EINVAL; > > > + } else if ((flags & O_DIRECTORY) && (flags & OPENAT2_REGULAR)) { > > > + return -EINVAL; > > > } > > > if (flags & O_PATH) { > > > /* O_PATH only permits certain other flags to be set. */ > > > diff --git a/fs/smb/client/dir.c b/fs/smb/client/dir.c > > > index cb10088197d2..d12ed0c87599 100644 > > > --- a/fs/smb/client/dir.c > > > +++ b/fs/smb/client/dir.c > > > @@ -236,6 +236,11 @@ static int cifs_do_create(struct inode *inode, > > > struct dentry *direntry, unsigned > > > * lookup. > > > */ > > > CIFSSMBClose(xid, tcon, fid->netfid); > > > + if (oflags & OPENAT2_REGULAR) { > > > + iput(newinode); > > > + rc = -EFTYPE; > > > + goto out; > > > + } > > > goto cifs_create_get_file_info; > > > } > > > /* success, no need to query */ > > > @@ -433,11 +438,15 @@ static int cifs_do_create(struct inode *inode, > > > struct dentry *direntry, unsigned > > > goto out_err; > > > } > > > > > > - if (newinode) > > > + if (newinode) { > > > if (S_ISDIR(newinode->i_mode)) { > > > rc = -EISDIR; > > > goto out_err; > > > > This logic doesn't look quite right. If you do a create and race with a > > directory create, then it looks like you'll send back -EISDIR here > > instead of -EFTYPE? > > > > Yes, I thought it would be useful for the caller to know what type of > file it actually is so I had kept this the same. Let me know if it is > preferable to return -EFTYPE always. > > Thanks for reviewing! > > Regards, > Dorjoy -- Jeff Layton <[email protected]>
