[PATCH v2 4/5] xfs: introduce XFS_DIFLAG2_IOMAP_IMMUTABLE

[Dan Williams]

Add an on-disk inode flag to record the state of the S_IOMAP_IMMUTABLE
in-memory vfs inode flags. This allows the protections against reflink
and hole punch to be automatically restored on a sub-sequent boot when
the in-memory inode is established.

The FS_XFLAG_IOMAP_IMMUTABLE is introduced to allow xfs_io to read the
state of the flag, but toggling the flag requires going through
fallocate(FALLOC_FL_[UN]SEAL_BLOCK_MAP). Support for toggling this
on-disk state is saved for a later patch.

Cc: Jan Kara <jack@xxxxxxx>
Cc: Jeff Moyer <jmoyer@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Suggested-by: Dave Chinner <david@xxxxxxxxxxxxx>
Suggested-by: "Darrick J. Wong" <darrick.wong@xxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
 fs/xfs/libxfs/xfs_format.h |    5 ++++-
 fs/xfs/xfs_inode.c         |    2 ++
 fs/xfs/xfs_ioctl.c         |    1 +
 fs/xfs/xfs_iops.c          |    8 +++++---
 include/uapi/linux/fs.h    |    1 +
 5 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
index d4d9bef20c3a..9e720e55776b 100644
--- a/fs/xfs/libxfs/xfs_format.h
+++ b/fs/xfs/libxfs/xfs_format.h
@@ -1063,12 +1063,15 @@ static inline void xfs_dinode_put_rdev(struct xfs_dinode *dip, xfs_dev_t rdev)
 #define XFS_DIFLAG2_DAX_BIT	0	/* use DAX for this inode */
 #define XFS_DIFLAG2_REFLINK_BIT	1	/* file's blocks may be shared */
 #define XFS_DIFLAG2_COWEXTSIZE_BIT   2  /* copy on write extent size hint */
+#define XFS_DIFLAG2_IOMAP_IMMUTABLE_BIT 3 /* set S_IOMAP_IMMUTABLE for this inode */
 #define XFS_DIFLAG2_DAX		(1 << XFS_DIFLAG2_DAX_BIT)
 #define XFS_DIFLAG2_REFLINK     (1 << XFS_DIFLAG2_REFLINK_BIT)
 #define XFS_DIFLAG2_COWEXTSIZE  (1 << XFS_DIFLAG2_COWEXTSIZE_BIT)
+#define XFS_DIFLAG2_IOMAP_IMMUTABLE (1 << XFS_DIFLAG2_IOMAP_IMMUTABLE_BIT)
 
 #define XFS_DIFLAG2_ANY \
-	(XFS_DIFLAG2_DAX | XFS_DIFLAG2_REFLINK | XFS_DIFLAG2_COWEXTSIZE)
+	(XFS_DIFLAG2_DAX | XFS_DIFLAG2_REFLINK | XFS_DIFLAG2_COWEXTSIZE | \
+	 XFS_DIFLAG2_IOMAP_IMMUTABLE)
 
 /*
  * Inode number format:
diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index ceef77c0416a..4ca22e272ce6 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -674,6 +674,8 @@ _xfs_dic2xflags(
 			flags |= FS_XFLAG_DAX;
 		if (di_flags2 & XFS_DIFLAG2_COWEXTSIZE)
 			flags |= FS_XFLAG_COWEXTSIZE;
+		if (di_flags2 & XFS_DIFLAG2_IOMAP_IMMUTABLE)
+			flags |= FS_XFLAG_IOMAP_IMMUTABLE;
 	}
 
 	if (has_attr)
diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index 2e64488bc4de..df2eef0f9d45 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -978,6 +978,7 @@ xfs_set_diflags(
 		return;
 
 	di_flags2 = (ip->i_d.di_flags2 & XFS_DIFLAG2_REFLINK);
+	di_flags2 |= (ip->i_d.di_flags2 & XFS_DIFLAG2_IOMAP_IMMUTABLE);
 	if (xflags & FS_XFLAG_DAX)
 		di_flags2 |= XFS_DIFLAG2_DAX;
 	if (xflags & FS_XFLAG_COWEXTSIZE)
diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index 469c9fa4c178..174ef95453f5 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -1186,9 +1186,10 @@ xfs_diflags_to_iflags(
 	struct xfs_inode	*ip)
 {
 	uint16_t		flags = ip->i_d.di_flags;
+	uint64_t		flags2 = ip->i_d.di_flags2;
 
 	inode->i_flags &= ~(S_IMMUTABLE | S_APPEND | S_SYNC |
-			    S_NOATIME | S_DAX);
+			    S_NOATIME | S_DAX | S_IOMAP_IMMUTABLE);
 
 	if (flags & XFS_DIFLAG_IMMUTABLE)
 		inode->i_flags |= S_IMMUTABLE;
@@ -1201,9 +1202,10 @@ xfs_diflags_to_iflags(
 	if (S_ISREG(inode->i_mode) &&
 	    ip->i_mount->m_sb.sb_blocksize == PAGE_SIZE &&
 	    !xfs_is_reflink_inode(ip) &&
-	    (ip->i_mount->m_flags & XFS_MOUNT_DAX ||
-	     ip->i_d.di_flags2 & XFS_DIFLAG2_DAX))
+	    (ip->i_mount->m_flags & XFS_MOUNT_DAX || flags2 & XFS_DIFLAG2_DAX))
 		inode->i_flags |= S_DAX;
+	if (flags2 & XFS_DIFLAG2_IOMAP_IMMUTABLE)
+		inode->i_flags |= S_IOMAP_IMMUTABLE;
 }
 
 /*
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index b7495d05e8de..4765e024ad74 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -182,6 +182,7 @@ struct fsxattr {
 #define FS_XFLAG_FILESTREAM	0x00004000	/* use filestream allocator */
 #define FS_XFLAG_DAX		0x00008000	/* use DAX for IO */
 #define FS_XFLAG_COWEXTSIZE	0x00010000	/* CoW extent size allocator hint */
+#define FS_XFLAG_IOMAP_IMMUTABLE 0x00020000	/* block map immutable */
 #define FS_XFLAG_HASATTR	0x80000000	/* no DIFLAG for this	*/
 
 /* the read-only stuff doesn't really belong here, but any other place is