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Message-ID: <20250422-gefressen-faucht-8ded2c9a5375@brauner>
Date: Tue, 22 Apr 2025 17:14:10 +0200
From: Christian Brauner <brauner@...nel.org>
To: Amir Goldstein <amir73il@...il.com>
Cc: Andrey Albershteyn <aalbersh@...hat.com>,
Richard Henderson <richard.henderson@...aro.org>, Matt Turner <mattst88@...il.com>,
Russell King <linux@...linux.org.uk>, Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>, Geert Uytterhoeven <geert@...ux-m68k.org>,
Michal Simek <monstr@...str.eu>, Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
"James E.J. Bottomley" <James.Bottomley@...senpartnership.com>, Helge Deller <deller@....de>,
Madhavan Srinivasan <maddy@...ux.ibm.com>, Michael Ellerman <mpe@...erman.id.au>,
Nicholas Piggin <npiggin@...il.com>, Christophe Leroy <christophe.leroy@...roup.eu>,
Naveen N Rao <naveen@...nel.org>, Heiko Carstens <hca@...ux.ibm.com>,
Vasily Gorbik <gor@...ux.ibm.com>, Alexander Gordeev <agordeev@...ux.ibm.com>,
Christian Borntraeger <borntraeger@...ux.ibm.com>, Sven Schnelle <svens@...ux.ibm.com>,
Yoshinori Sato <ysato@...rs.sourceforge.jp>, Rich Felker <dalias@...c.org>,
John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>, "David S. Miller" <davem@...emloft.net>,
Andreas Larsson <andreas@...sler.com>, Andy Lutomirski <luto@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
Chris Zankel <chris@...kel.net>, Max Filippov <jcmvbkbc@...il.com>,
Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>,
Mickaël Salaün <mic@...ikod.net>, Günther Noack <gnoack@...gle.com>,
Arnd Bergmann <arnd@...db.de>, Pali Rohár <pali@...nel.org>,
Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
"Serge E. Hallyn" <serge@...lyn.com>, linux-alpha@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, linux-m68k@...ts.linux-m68k.org, linux-mips@...r.kernel.org,
linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
linux-sh@...r.kernel.org, sparclinux@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-security-module@...r.kernel.org, linux-api@...r.kernel.org, linux-arch@...r.kernel.org,
linux-xfs@...r.kernel.org
Subject: Re: [PATCH v4 3/3] fs: introduce getfsxattrat and setfsxattrat
syscalls
On Tue, Apr 22, 2025 at 04:31:29PM +0200, Christian Brauner wrote:
> On Thu, Mar 27, 2025 at 12:39:28PM +0100, Amir Goldstein wrote:
> > On Thu, Mar 27, 2025 at 10:33 AM Andrey Albershteyn <aalbersh@...hat.com> wrote:
> > >
> > > On 2025-03-23 09:56:25, Amir Goldstein wrote:
> > > > On Fri, Mar 21, 2025 at 8:49 PM Andrey Albershteyn <aalbersh@...hat.com> wrote:
> > > > >
> > > > > From: Andrey Albershteyn <aalbersh@...hat.com>
> > > > >
> > > > > Introduce getfsxattrat and setfsxattrat syscalls to manipulate inode
> > > > > extended attributes/flags. The syscalls take parent directory fd and
> > > > > path to the child together with struct fsxattr.
> > > > >
> > > > > This is an alternative to FS_IOC_FSSETXATTR ioctl with a difference
> > > > > that file don't need to be open as we can reference it with a path
> > > > > instead of fd. By having this we can manipulated inode extended
> > > > > attributes not only on regular files but also on special ones. This
> > > > > is not possible with FS_IOC_FSSETXATTR ioctl as with special files
> > > > > we can not call ioctl() directly on the filesystem inode using fd.
> > > > >
> > > > > This patch adds two new syscalls which allows userspace to get/set
> > > > > extended inode attributes on special files by using parent directory
> > > > > and a path - *at() like syscall.
> > > > >
> > > > > CC: linux-api@...r.kernel.org
> > > > > CC: linux-fsdevel@...r.kernel.org
> > > > > CC: linux-xfs@...r.kernel.org
> > > > > Signed-off-by: Andrey Albershteyn <aalbersh@...hat.com>
> > > > > Acked-by: Arnd Bergmann <arnd@...db.de>
> > > > > ---
> > > > ...
> > > > > +SYSCALL_DEFINE5(setfsxattrat, int, dfd, const char __user *, filename,
> > > > > + struct fsxattr __user *, ufsx, size_t, usize,
> > > > > + unsigned int, at_flags)
> > > > > +{
> > > > > + struct fileattr fa;
> > > > > + struct path filepath;
> > > > > + int error;
> > > > > + unsigned int lookup_flags = 0;
> > > > > + struct filename *name;
> > > > > + struct mnt_idmap *idmap;.
> > > >
> > > > > + struct dentry *dentry;
> > > > > + struct vfsmount *mnt;
> > > > > + struct fsxattr fsx = {};
> > > > > +
> > > > > + BUILD_BUG_ON(sizeof(struct fsxattr) < FSXATTR_SIZE_VER0);
> > > > > + BUILD_BUG_ON(sizeof(struct fsxattr) != FSXATTR_SIZE_LATEST);
> > > > > +
> > > > > + if ((at_flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
> > > > > + return -EINVAL;
> > > > > +
> > > > > + if (!(at_flags & AT_SYMLINK_NOFOLLOW))
> > > > > + lookup_flags |= LOOKUP_FOLLOW;
> > > > > +
> > > > > + if (at_flags & AT_EMPTY_PATH)
> > > > > + lookup_flags |= LOOKUP_EMPTY;
> > > > > +
> > > > > + if (usize > PAGE_SIZE)
> > > > > + return -E2BIG;
> > > > > +
> > > > > + if (usize < FSXATTR_SIZE_VER0)
> > > > > + return -EINVAL;
> > > > > +
> > > > > + error = copy_struct_from_user(&fsx, sizeof(struct fsxattr), ufsx, usize);
> > > > > + if (error)
> > > > > + return error;
> > > > > +
> > > > > + fsxattr_to_fileattr(&fsx, &fa);
> > > > > +
> > > > > + name = getname_maybe_null(filename, at_flags);
> > > > > + if (!name) {
> > > > > + CLASS(fd, f)(dfd);
> > > > > +
> > > > > + if (fd_empty(f))
> > > > > + return -EBADF;
> > > > > +
> > > > > + idmap = file_mnt_idmap(fd_file(f));
> > > > > + dentry = file_dentry(fd_file(f));
> > > > > + mnt = fd_file(f)->f_path.mnt;
> > > > > + } else {
> > > > > + error = filename_lookup(dfd, name, lookup_flags, &filepath,
> > > > > + NULL);
> > > > > + if (error)
> > > > > + return error;
> > > > > +
> > > > > + idmap = mnt_idmap(filepath.mnt);
> > > > > + dentry = filepath.dentry;
> > > > > + mnt = filepath.mnt;
> > > > > + }
> > > > > +
> > > > > + error = mnt_want_write(mnt);
> > > > > + if (!error) {
> > > > > + error = vfs_fileattr_set(idmap, dentry, &fa);
> > > > > + if (error == -ENOIOCTLCMD)
> > > > > + error = -EOPNOTSUPP;
> > > >
> > > > This is awkward.
> > > > vfs_fileattr_set() should return -EOPNOTSUPP.
> > > > ioctl_setflags() could maybe convert it to -ENOIOCTLCMD,
> > > > but looking at similar cases ioctl_fiemap(), ioctl_fsfreeze() the
> > > > ioctl returns -EOPNOTSUPP.
> > > >
> > > > I don't think it is necessarily a bad idea to start returning
> > > > -EOPNOTSUPP instead of -ENOIOCTLCMD for the ioctl
> > > > because that really reflects the fact that the ioctl is now implemented
> > > > in vfs and not in the specific fs.
> > > >
> > > > and I think it would not be a bad idea at all to make that change
> > > > together with the merge of the syscalls as a sort of hint to userspace
> > > > that uses the ioctl, that the sycalls API exists.
> > > >
> > > > Thanks,
> > > > Amir.
> > > >
> > >
> > > Hmm, not sure what you're suggesting here. I see it as:
> > > - get/setfsxattrat should return EOPNOTSUPP as it make more sense
> > > than ENOIOCTLCMD
> > > - ioctl_setflags returns ENOIOCTLCMD which also expected
> > >
> > > Don't really see a reason to change what vfs_fileattr_set() returns
> > > and then copying this if() to other places or start returning
> > > EOPNOTSUPP.
> >
> > ENOIOCTLCMD conceptually means that the ioctl command is unknown
> > This is not the case since ->fileattr_[gs]et() became a vfs API
>
> vfs_fileattr_{g,s}et() should not return ENOIOCTLCMD. Change the return
> code to EOPNOTSUPP and then make EOPNOTSUPP be translated to ENOTTY on
> on overlayfs and to ENOIOCTLCMD in ecryptfs and in fs/ioctl.c. This way
> we get a clean VFS api while retaining current behavior. Amir can do his
> cleanup based on that.
Also this get/set dance is not something new apis should do. It should
be handled like setattr_prepare() or generic_fillattr() where the
filesystem calls a VFS helper and that does all of this based on the
current state of the inode instead of calling into the filesystem twice:
int vfs_fileattr_set(struct mnt_idmap *idmap, struct dentry *dentry,
struct fileattr *fa)
{
<snip>
inode_lock(inode);
err = vfs_fileattr_get(dentry, &old_ma);
if (!err) {
/* initialize missing bits from old_ma */
if (fa->flags_valid) {
<snip>
err = fileattr_set_prepare(inode, &old_ma, fa);
if (!err && !security_inode_setfsxattr(inode, fa))
err = inode->i_op->fileattr_set(idmap, dentry, fa);
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