On Fri, Mar 21, 2025 at 8:49 PM Andrey Albershteyn <aalbersh@xxxxxxxxxx> wrote:
>
> From: Andrey Albershteyn <aalbersh@xxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxx
> CC: linux-fsdevel@xxxxxxxxxxxxxxx
> CC: linux-xfs@xxxxxxxxxxxxxxx
> Signed-off-by: Andrey Albershteyn <aalbersh@xxxxxxxxxx>
> Acked-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
...
> +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.
