On Fri 21-03-25 20:48:42, Andrey Albershteyn wrote:

From: Andrey Albershteyn <redacted>

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@vger.kernel.org
CC: linux-fsdevel@vger.kernel.org
CC: linux-xfs@vger.kernel.org
Signed-off-by: Andrey Albershteyn <redacted>
Acked-by: Arnd Bergmann <arnd@arndb.de>

Looks good. Just two nits below:

+SYSCALL_DEFINE5(getfsxattrat, 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 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;

Strictly speaking setting LOOKUP_EMPTY does not have any effect because
empty names are already handled by getname_maybe_null(). But it does not
hurt either so I don't really care...

+
+	if (usize > PAGE_SIZE)
+		return -E2BIG;
+
+	if (usize < FSXATTR_SIZE_VER0)
+		return -EINVAL;
+
+	name = getname_maybe_null(filename, at_flags);
+	if (!name) {
+		CLASS(fd, f)(dfd);
+
+		if (fd_empty(f))
+			return -EBADF;
+		error = vfs_fileattr_get(file_dentry(fd_file(f)), &fa);
+	} else {
+		error = filename_lookup(dfd, name, lookup_flags, &filepath,
+					NULL);
+		if (error)
+			goto out;
+		error = vfs_fileattr_get(filepath.dentry, &fa);
+		path_put(&filepath);
+	}
+	if (error == -ENOIOCTLCMD)
+		error = -EOPNOTSUPP;
+	if (!error) {
+		fileattr_to_fsxattr(&fa, &fsx);
+		error = copy_struct_to_user(ufsx, usize, &fsx,
+					    sizeof(struct fsxattr), NULL);
+	}
+out:
+	putname(name);
+	return error;
+}
+
+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;

Same comment regarding LOOKUP_EMPTY here.

+
+	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;
+		mnt_drop_write(mnt);
+	}
+
+	path_put(&filepath);

filepath will not be initialized here in case of name == NULL. 

+	return error;
+}

With this fixed feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

-- 
Jan Kara [off-list ref]
SUSE Labs, CR