On Thu, Mar 27, 2025 at 12:39:28PM +0100, Amir Goldstein wrote:
> On Thu, Mar 27, 2025 at 10:33 AM Andrey Albershteyn <aalbe...@redhat.com>
> wrote:
> >
> > On 2025-03-23 09:56:25, Amir Goldstein wrote:
> > > On Fri, Mar 21, 2025 at 8:49 PM Andrey Albershteyn <aalbe...@redhat.com>
> > > wrote:
> > > >
> > > > From: Andrey Albershteyn <aalbe...@redhat.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-...@vger.kernel.org
> > > > CC: linux-fsde...@vger.kernel.org
> > > > CC: linux-...@vger.kernel.org
> > > > Signed-off-by: Andrey Albershteyn <aalbe...@redhat.com>
> > > > Acked-by: Arnd Bergmann <a...@arndb.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.
