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[PATCH 0/3] fs, xfs: block map immutable files for dax, dma-to-storage, and swap

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  [PATCH 0/3] fs, xfs: block map immutable files for dax,  dma-to-storage, and swap Dan Williams <dan.j.williams@intel.com> - 2017-07-29 22:00 +0200
    [PATCH 3/3] xfs: persist S_IOMAP_IMMUTABLE in di_flags2 Dan Williams <dan.j.williams@intel.com> - 2017-07-29 22:00 +0200
    [PATCH 2/3] fs, xfs: introduce FALLOC_FL_SEAL_BLOCK_MAP Dan Williams <dan.j.williams@intel.com> - 2017-07-29 22:00 +0200
    [PATCH 1/3] fs, xfs: introduce S_IOMAP_IMMUTABLE Dan Williams <dan.j.williams@intel.com> - 2017-07-29 22:00 +0200

#1699356 — [PATCH 0/3] fs, xfs: block map immutable files for dax, dma-to-storage, and swap

tl;dr: The proposed S_IOMAP_IMMUTABLE mechanism

The daxfile proposal a few weeks back [1] sought to piggy back on the
swapfile implementation to approximate a block map immutable file. This
is an idea Dave originated last year to solve the dax "flush from
userspace" problem [2].

The discussion yielded several results. First, Christoph pointed out that
swapfiles are subtly broken [3].  Second, Darrick [4]
and Dave [5] proposed how to properly implement a block map immutable file.
Finally, Dave identified some improvements to swapfiles that can be
built on the block-map-immutable mecahanism. These patches seek to
implement the first part of the proposal and save the swapfile work to
build on top once the base mechanism is complete.

While the initial motivation for this feature is support for
byte-addressable updates of persistent memory and managing cache
maintenance from userspace, the applications of the feature are broader.
In addition to being the start of a better swapfile mechanism it can
also support a DMA-to-storage use case.  This use case enables
data-acquisition hardware to DMA directly to a storage device address
while being safe in the knowledge that storage mappings will not change.

These patches are relative to Darrick's 'devel' tree. Patch 3 is likely
wrong in the way it sets the new XFS_DIFLAG2_IOMAP_IMMUTABLE flag, but
seems to work with a basic test. The test just turns the flag on and
off, checks that the file is fully allocated and immutable, and
validates that the state persists over a umount / mount cycle. A proper
xfstest is in the works, but comments on this first draft are welcome.

[1]: https://lkml.org/lkml/2017/6/16/790
[2]: https://lkml.org/lkml/2016/9/11/159
[3]: https://lkml.org/lkml/2017/6/18/31
[4]: https://lkml.org/lkml/2017/6/20/49
[5]: https://www.spinics.net/lists/linux-xfs/msg07871.html

---

Dan Williams (3):
      fs, xfs: introduce S_IOMAP_IMMUTABLE
      fs, xfs: introduce FALLOC_FL_SEAL_BLOCK_MAP
      xfs: persist S_IOMAP_IMMUTABLE in di_flags2


 fs/attr.c                   |   10 ++++
 fs/namei.c                  |    3 +
 fs/open.c                   |   28 ++++++++++++
 fs/read_write.c             |    3 +
 fs/xfs/libxfs/xfs_format.h  |    5 ++
 fs/xfs/xfs_bmap_util.c      |   98 ++++++++++++++++++++++++++++++++++++++++++-
 fs/xfs/xfs_bmap_util.h      |    4 +-
 fs/xfs/xfs_file.c           |   14 ++++--
 fs/xfs/xfs_ioctl.c          |   10 ++++
 fs/xfs/xfs_iops.c           |    8 ++--
 include/linux/falloc.h      |    3 +
 include/linux/fs.h          |    2 +
 include/uapi/linux/falloc.h |   19 ++++++++
 mm/filemap.c                |    9 ++++
 14 files changed, 200 insertions(+), 16 deletions(-)

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#1699357 — [PATCH 3/3] xfs: persist S_IOMAP_IMMUTABLE in di_flags2

Record the immutable state in the on-disk inode so that on the next boot
the protections against reflink and hole punch etc are automatically
restored.

This deliberately does not add a FS_XFLAG_IOMAP_IMMUTABLE since
fallocate(2) is the path to toggle this flag.

Cc: Jan Kara <jack@suse.cz>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Suggested-by: Dave Chinner <david@fromorbit.com>
Suggested-by: "Darrick J. Wong" <darrick.wong@oracle.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 fs/xfs/libxfs/xfs_format.h |    5 ++++-
 fs/xfs/xfs_bmap_util.c     |   14 +++++++++++---
 fs/xfs/xfs_bmap_util.h     |    2 +-
 fs/xfs/xfs_file.c          |    4 ++--
 fs/xfs/xfs_ioctl.c         |    4 ++--
 fs/xfs/xfs_iops.c          |    8 +++++---
 6 files changed, 25 insertions(+), 12 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_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index c4fc79a0704f..1dcb521da456 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -1021,7 +1021,8 @@ xfs_alloc_file_space(
 	struct xfs_inode	*ip,
 	xfs_off_t		offset,
 	xfs_off_t		len,
-	int			alloc_type)
+	int			alloc_type,
+	uint64_t		di_flags2)
 {
 	xfs_mount_t		*mp = ip->i_mount;
 	xfs_off_t		count;
@@ -1119,6 +1120,12 @@ xfs_alloc_file_space(
 			break;
 		}
 		xfs_ilock(ip, XFS_ILOCK_EXCL);
+		if (di_flags2) {
+			/* fold inode attributes for this allocation */
+			ip->i_d.di_flags2 |= di_flags2;
+			di_flags2 = 0;
+		}
+
 		error = xfs_trans_reserve_quota_nblks(tp, ip, qblocks,
 						      0, quota_flag);
 		if (error)
@@ -1381,7 +1388,7 @@ xfs_zero_file_space(
 	error = xfs_alloc_file_space(ip, round_down(offset, blksize),
 				     round_up(offset + len, blksize) -
 				     round_down(offset, blksize),
-				     XFS_BMAPI_PREALLOC);
+				     XFS_BMAPI_PREALLOC, 0);
 out:
 	return error;
 
@@ -1461,7 +1468,8 @@ xfs_seal_file_space(
 		goto err;
 
 	error = xfs_alloc_file_space(ip, offset, len,
-			XFS_BMAPI_CONVERT | XFS_BMAPI_ZERO);
+			XFS_BMAPI_CONVERT | XFS_BMAPI_ZERO,
+			XFS_DIFLAG2_IOMAP_IMMUTABLE);
 	if (error)
 		goto err;
 
diff --git a/fs/xfs/xfs_bmap_util.h b/fs/xfs/xfs_bmap_util.h
index 5115a32a2483..1698e0c58b78 100644
--- a/fs/xfs/xfs_bmap_util.h
+++ b/fs/xfs/xfs_bmap_util.h
@@ -51,7 +51,7 @@ int	xfs_bmap_last_extent(struct xfs_trans *tp, struct xfs_inode *ip,
 
 /* preallocation and hole punch interface */
 int	xfs_alloc_file_space(struct xfs_inode *ip, xfs_off_t offset,
-			     xfs_off_t len, int alloc_type);
+			     xfs_off_t len, int alloc_type, uint64_t di_flags2);
 int	xfs_free_file_space(struct xfs_inode *ip, xfs_off_t offset,
 			    xfs_off_t len);
 int	xfs_zero_file_space(struct xfs_inode *ip, xfs_off_t offset,
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index e21121530a90..2d9ffa1773bd 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -837,12 +837,12 @@ xfs_file_fallocate(
 					goto out_unlock;
 
 				error = xfs_alloc_file_space(ip, offset, len,
-						XFS_BMAPI_PREALLOC);
+						XFS_BMAPI_PREALLOC, 0);
 			} else if (mode & FALLOC_FL_SEAL_BLOCK_MAP) {
 				error = xfs_seal_file_space(ip, offset, len);
 			} else
 				error = xfs_alloc_file_space(ip, offset, len,
-						XFS_BMAPI_PREALLOC);
+						XFS_BMAPI_PREALLOC, 0);
 		}
 		if (error)
 			goto out_unlock;
diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index 2e64488bc4de..c829f85bed99 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -703,7 +703,7 @@ xfs_ioc_space(
 	case XFS_IOC_RESVSP64:
 		flags |= XFS_PREALLOC_SET;
 		error = xfs_alloc_file_space(ip, bf->l_start, bf->l_len,
-						XFS_BMAPI_PREALLOC);
+						XFS_BMAPI_PREALLOC, 0);
 		break;
 	case XFS_IOC_UNRESVSP:
 	case XFS_IOC_UNRESVSP64:
@@ -716,7 +716,7 @@ xfs_ioc_space(
 		flags |= XFS_PREALLOC_CLEAR;
 		if (bf->l_start > XFS_ISIZE(ip)) {
 			error = xfs_alloc_file_space(ip, XFS_ISIZE(ip),
-					bf->l_start - XFS_ISIZE(ip), 0);
+					bf->l_start - XFS_ISIZE(ip), 0, 0);
 			if (error)
 				goto out_unlock;
 		}
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;
 }
 
 /*

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#1699358 — [PATCH 2/3] fs, xfs: introduce FALLOC_FL_SEAL_BLOCK_MAP

>From falloc.h:

    FALLOC_FL_SEAL_BLOCK_MAP is used to seal (make immutable) all of the
    file logical-to-physical extent offset mappings in the file. The
    purpose is to allow an application to assume that there are no holes
    or shared extents in the file and that the metadata needed to find
    all the physical extents of the file is stable and can never be
    dirtied.

For now this patch only permits setting / clearing the in-memory state
of S_IOMAP_IMMMUTABLE, persisting the state is saved for a later patch.

The implementation is careful to not allow the immutable state to change
while any process might have any established mappings. It reuses the
existing xfs_reflink_unshare() and xfs_alloc_file_space() to unshare
extents and fill all holes in the file, or otherwise extend the file
size in the same operation that sets S_IOMAP_IMMUTABLE.

Cc: Jan Kara <jack@suse.cz>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Suggested-by: Dave Chinner <david@fromorbit.com>
Suggested-by: "Darrick J. Wong" <darrick.wong@oracle.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 fs/open.c                   |   26 ++++++++++++-
 fs/xfs/xfs_bmap_util.c      |   86 +++++++++++++++++++++++++++++++++++++++++++
 fs/xfs/xfs_bmap_util.h      |    2 +
 fs/xfs/xfs_file.c           |   14 +++++--
 include/linux/falloc.h      |    3 +-
 include/uapi/linux/falloc.h |   19 ++++++++++
 6 files changed, 142 insertions(+), 8 deletions(-)

diff --git a/fs/open.c b/fs/open.c
index 7395860d7164..df075484fad5 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -241,7 +241,11 @@ int vfs_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 	struct inode *inode = file_inode(file);
 	long ret;
 
-	if (offset < 0 || len <= 0)
+	if (offset < 0 || len < 0)
+		return -EINVAL;
+
+	/* Allow zero len only for the unseal operation */
+	if (!(mode & FALLOC_FL_SEAL_BLOCK_MAP) && len == 0)
 		return -EINVAL;
 
 	/* Return error if mode is not supported */
@@ -273,6 +277,17 @@ int vfs_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 	    (mode & ~(FALLOC_FL_UNSHARE_RANGE | FALLOC_FL_KEEP_SIZE)))
 		return -EINVAL;
 
+	/*
+	 * Seal block map should only be used exclusively, and with
+	 * the IMMUTABLE capability.
+	 */
+	if (mode & FALLOC_FL_SEAL_BLOCK_MAP) {
+		if (mode & ~FALLOC_FL_SEAL_BLOCK_MAP)
+			return -EINVAL;
+		if (!capable(CAP_LINUX_IMMUTABLE))
+			return -EPERM;
+	}
+
 	if (!(file->f_mode & FMODE_WRITE))
 		return -EBADF;
 
@@ -292,9 +307,14 @@ int vfs_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 		return -ETXTBSY;
 
 	/*
-	 * We cannot allow any allocation changes on an iomap immutable file
+	 * We cannot allow any allocation changes on an iomap immutable
+	 * file, however if the operation is FALLOC_FL_SEAL_BLOCK_MAP,
+	 * call down to ->fallocate() to determine if the operations is
+	 * allowed. ->fallocate() may either clear the flag when @len is
+	 * zero, or validate that the requested operation is already the
+	 * current state of the file.
 	 */
-	if (IS_IOMAP_IMMUTABLE(inode))
+	if (IS_IOMAP_IMMUTABLE(inode) && (!(mode & FALLOC_FL_SEAL_BLOCK_MAP)))
 		return -ETXTBSY;
 
 	/*
diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index 93e955262d07..c4fc79a0704f 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -1387,6 +1387,92 @@ xfs_zero_file_space(
 
 }
 
+int
+xfs_seal_file_space(
+	struct xfs_inode	*ip,
+	xfs_off_t		offset,
+	xfs_off_t		len)
+{
+	struct inode		*inode = VFS_I(ip);
+	struct address_space	*mapping = inode->i_mapping;
+	int			error = 0;
+
+	if (offset)
+		return -EINVAL;
+
+	i_mmap_lock_read(mapping);
+	xfs_ilock(ip, XFS_ILOCK_EXCL);
+	if (len == 0) {
+		/*
+		 * Clear the immutable flag provided there are no active
+		 * mappings. The active mapping check prevents an
+		 * application that is assuming a static block map, for
+		 * DAX or peer-to-peer DMA, from having this state
+		 * silently change behind its back.
+		 */
+		if (RB_EMPTY_ROOT(&mapping->i_mmap))
+			inode->i_flags &= ~S_IOMAP_IMMUTABLE;
+		else
+			error = -EBUSY;
+	} else if (IS_IOMAP_IMMUTABLE(inode)) {
+		if (len == i_size_read(inode)) {
+			/*
+			 * The file is already in the correct state,
+			 * bail out without error below.
+			 */
+			len = 0;
+		} else {
+			/* too late to allocate more space */
+			error = -ETXTBSY;
+		}
+	} else {
+		if (len < i_size_read(inode)) {
+			/*
+			 * Since S_IOMAP_IMMUTABLE is inode global it
+			 * does not make sense to fallocate(immutable)
+			 * on a sub-range of the file.
+			 */
+			error = -EINVAL;
+		} else if (!RB_EMPTY_ROOT(&mapping->i_mmap)) {
+			/*
+			 * It's not strictly required to prevent setting
+			 * immutable while a file is already mapped, but
+			 * we do it for simplicity and symmetry with the
+			 * S_IOMAP_IMMUTABLE disable case.
+			 */
+			error = -EBUSY;
+		} else
+			inode->i_flags |= S_IOMAP_IMMUTABLE;
+	}
+	xfs_iunlock(ip, XFS_ILOCK_EXCL);
+	i_mmap_unlock_read(mapping);
+
+	if (error || len == 0)
+		return error;
+
+	/*
+	 * From here, the immutable flag is already set, so new
+	 * operations that would change the block map are prevented by
+	 * upper layer code paths. Wwe can proceed to unshare and
+	 * allocate zeroed / written extents.
+	 */
+	error = xfs_reflink_unshare(ip, offset, len);
+	if (error)
+		goto err;
+
+	error = xfs_alloc_file_space(ip, offset, len,
+			XFS_BMAPI_CONVERT | XFS_BMAPI_ZERO);
+	if (error)
+		goto err;
+
+	return 0;
+err:
+	xfs_ilock(ip, XFS_ILOCK_EXCL);
+	inode->i_flags &= ~S_IOMAP_IMMUTABLE;
+	xfs_iunlock(ip, XFS_ILOCK_EXCL);
+	return error;
+}
+
 /*
  * @next_fsb will keep track of the extent currently undergoing shift.
  * @stop_fsb will keep track of the extent at which we have to stop.
diff --git a/fs/xfs/xfs_bmap_util.h b/fs/xfs/xfs_bmap_util.h
index 0cede1043571..5115a32a2483 100644
--- a/fs/xfs/xfs_bmap_util.h
+++ b/fs/xfs/xfs_bmap_util.h
@@ -60,6 +60,8 @@ int	xfs_collapse_file_space(struct xfs_inode *, xfs_off_t offset,
 				xfs_off_t len);
 int	xfs_insert_file_space(struct xfs_inode *, xfs_off_t offset,
 				xfs_off_t len);
+int	xfs_seal_file_space(struct xfs_inode *, xfs_off_t offset,
+				xfs_off_t len);
 
 /* EOF block manipulation functions */
 bool	xfs_can_free_eofblocks(struct xfs_inode *ip, bool force);
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index c4893e226fd8..e21121530a90 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -739,7 +739,8 @@ xfs_file_write_iter(
 #define	XFS_FALLOC_FL_SUPPORTED						\
 		(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |		\
 		 FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_ZERO_RANGE |	\
-		 FALLOC_FL_INSERT_RANGE | FALLOC_FL_UNSHARE_RANGE)
+		 FALLOC_FL_INSERT_RANGE | FALLOC_FL_UNSHARE_RANGE |	\
+		 FALLOC_FL_SEAL_BLOCK_MAP)
 
 STATIC long
 xfs_file_fallocate(
@@ -834,9 +835,14 @@ xfs_file_fallocate(
 				error = xfs_reflink_unshare(ip, offset, len);
 				if (error)
 					goto out_unlock;
-			}
-			error = xfs_alloc_file_space(ip, offset, len,
-						     XFS_BMAPI_PREALLOC);
+
+				error = xfs_alloc_file_space(ip, offset, len,
+						XFS_BMAPI_PREALLOC);
+			} else if (mode & FALLOC_FL_SEAL_BLOCK_MAP) {
+				error = xfs_seal_file_space(ip, offset, len);
+			} else
+				error = xfs_alloc_file_space(ip, offset, len,
+						XFS_BMAPI_PREALLOC);
 		}
 		if (error)
 			goto out_unlock;
diff --git a/include/linux/falloc.h b/include/linux/falloc.h
index 7494dc67c66f..48546c6fbec7 100644
--- a/include/linux/falloc.h
+++ b/include/linux/falloc.h
@@ -26,6 +26,7 @@ struct space_resv {
 					 FALLOC_FL_COLLAPSE_RANGE |	\
 					 FALLOC_FL_ZERO_RANGE |		\
 					 FALLOC_FL_INSERT_RANGE |	\
-					 FALLOC_FL_UNSHARE_RANGE)
+					 FALLOC_FL_UNSHARE_RANGE |	\
+					 FALLOC_FL_SEAL_BLOCK_MAP)
 
 #endif /* _FALLOC_H_ */
diff --git a/include/uapi/linux/falloc.h b/include/uapi/linux/falloc.h
index b075f601919b..629c9b20e49b 100644
--- a/include/uapi/linux/falloc.h
+++ b/include/uapi/linux/falloc.h
@@ -76,4 +76,23 @@
  */
 #define FALLOC_FL_UNSHARE_RANGE		0x40
 
+/*
+ * FALLOC_FL_SEAL_BLOCK_MAP is used to seal (make immutable) all of the
+ * file logical-to-physical extent offset mappings in the file. The
+ * purpose is to allow an application to assume that there are no holes
+ * or shared extents in the file and that the metadata needed to find
+ * all the physical extents of the file is stable and can never be
+ * dirtied.
+ *
+ * The immutable property is in effect for the entire inode, so the
+ * range for this operation must start at offset 0 and len must be
+ * greater than or equal to the current size of the file. If greater,
+ * this operation allocates, unshares, hole fills, and seals in one
+ * atomic step. If len is zero then the immutable state is cleared for
+ * the inode.
+ *
+ * This flag implies FALLOC_FL_UNSHARE_RANGE and as such cannot be used
+ * with the punch, zero, collapse, or insert range modes.
+ */
+#define FALLOC_FL_SEAL_BLOCK_MAP	0x80
 #endif /* _UAPI_FALLOC_H_ */

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#1699359 — [PATCH 1/3] fs, xfs: introduce S_IOMAP_IMMUTABLE

An inode with this flag set indicates that the file's block map cannot
be changed, no size change, deletion, hole-punch, range collapse, or
reflink.

The implementation of toggling the flag and sealing the state of the
extent map is saved for a later patch. The functionality provided by
S_IOMAP_IMMUTABLE, once toggle support is added, will be a superset of
that provided by S_SWAPFILE, and it is targeted to replace it.

For now, only xfs and the core vfs are updated to consider the new flag.

The additional check that is added for this flag, beyond what we are
already doing for swapfiles, is to truncate or abort writes that try to
extend the file size.

Cc: Jan Kara <jack@suse.cz>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Suggested-by: Dave Chinner <david@fromorbit.com>
Suggested-by: "Darrick J. Wong" <darrick.wong@oracle.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 fs/attr.c          |   10 ++++++++++
 fs/namei.c         |    3 ++-
 fs/open.c          |    6 ++++++
 fs/read_write.c    |    3 +++
 fs/xfs/xfs_ioctl.c |    6 ++++++
 include/linux/fs.h |    2 ++
 mm/filemap.c       |    9 +++++++++
 7 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/fs/attr.c b/fs/attr.c
index 135304146120..8573e364bd06 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -112,6 +112,16 @@ EXPORT_SYMBOL(setattr_prepare);
  */
 int inode_newsize_ok(const struct inode *inode, loff_t offset)
 {
+	if (IS_IOMAP_IMMUTABLE(inode)) {
+		/*
+		 * Any size change is disallowed. Size increases may
+		 * dirty metadata that an application is not prepared to
+		 * sync, and a size decrease may expose free blocks to
+		 * in-flight DMA.
+		 */
+		return -ETXTBSY;
+	}
+
 	if (inode->i_size < offset) {
 		unsigned long limit;
 
diff --git a/fs/namei.c b/fs/namei.c
index ddb6a7c2b3d4..588f1135c42c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2793,7 +2793,8 @@ static int may_delete(struct inode *dir, struct dentry *victim, bool isdir)
 		return -EPERM;
 
 	if (check_sticky(dir, inode) || IS_APPEND(inode) ||
-	    IS_IMMUTABLE(inode) || IS_SWAPFILE(inode) || HAS_UNMAPPED_ID(inode))
+	    IS_IMMUTABLE(inode) || IS_SWAPFILE(inode) || HAS_UNMAPPED_ID(inode)
+	    || IS_IOMAP_IMMUTABLE(inode))
 		return -EPERM;
 	if (isdir) {
 		if (!d_is_dir(victim))
diff --git a/fs/open.c b/fs/open.c
index 35bb784763a4..7395860d7164 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -292,6 +292,12 @@ int vfs_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 		return -ETXTBSY;
 
 	/*
+	 * We cannot allow any allocation changes on an iomap immutable file
+	 */
+	if (IS_IOMAP_IMMUTABLE(inode))
+		return -ETXTBSY;
+
+	/*
 	 * Revalidate the write permissions, in case security policy has
 	 * changed since the files were opened.
 	 */
diff --git a/fs/read_write.c b/fs/read_write.c
index 0cc7033aa413..dc673be7c7cb 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1706,6 +1706,9 @@ int vfs_clone_file_prep_inodes(struct inode *inode_in, loff_t pos_in,
 	if (IS_SWAPFILE(inode_in) || IS_SWAPFILE(inode_out))
 		return -ETXTBSY;
 
+	if (IS_IOMAP_IMMUTABLE(inode_in) || IS_IOMAP_IMMUTABLE(inode_out))
+		return -ETXTBSY;
+
 	/* Don't reflink dirs, pipes, sockets... */
 	if (S_ISDIR(inode_in->i_mode) || S_ISDIR(inode_out->i_mode))
 		return -EISDIR;
diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index e75c40a47b7d..2e64488bc4de 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -1755,6 +1755,12 @@ xfs_ioc_swapext(
 		goto out_put_tmp_file;
 	}
 
+	if (IS_IOMAP_IMMUTABLE(file_inode(f.file)) ||
+	    IS_IOMAP_IMMUTABLE(file_inode(tmp.file))) {
+		error = -EINVAL;
+		goto out_put_tmp_file;
+	}
+
 	/*
 	 * We need to ensure that the fds passed in point to XFS inodes
 	 * before we cast and access them as XFS structures as we have no
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 6e1fd5d21248..0a254b768855 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1829,6 +1829,7 @@ struct super_operations {
 #else
 #define S_DAX		0	/* Make all the DAX code disappear */
 #endif
+#define S_IOMAP_IMMUTABLE 16384 /* logical-to-physical extent map is fixed */
 
 /*
  * Note that nosuid etc flags are inode-specific: setting some file-system
@@ -1867,6 +1868,7 @@ struct super_operations {
 #define IS_AUTOMOUNT(inode)	((inode)->i_flags & S_AUTOMOUNT)
 #define IS_NOSEC(inode)		((inode)->i_flags & S_NOSEC)
 #define IS_DAX(inode)		((inode)->i_flags & S_DAX)
+#define IS_IOMAP_IMMUTABLE(inode) ((inode)->i_flags & S_IOMAP_IMMUTABLE)
 
 #define IS_WHITEOUT(inode)	(S_ISCHR(inode->i_mode) && \
 				 (inode)->i_rdev == WHITEOUT_DEV)
diff --git a/mm/filemap.c b/mm/filemap.c
index a49702445ce0..e4a6529da2bd 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2806,6 +2806,15 @@ inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
 	if (unlikely(pos >= inode->i_sb->s_maxbytes))
 		return -EFBIG;
 
+	/* Are we about to mutate the block map on an immutable file? */
+	if (IS_IOMAP_IMMUTABLE(inode)
+			&& (pos + iov_iter_count(from) > i_size_read(inode))) {
+		if (pos < i_size_read(inode))
+			iov_iter_truncate(from, i_size_read(inode) - pos);
+		else
+			return -ETXTBSY;
+	}
+
 	iov_iter_truncate(from, inode->i_sb->s_maxbytes - pos);
 	return iov_iter_count(from);
 }

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