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.
--
- Andrey
