[PATCH v1 5/5] ntfs: support O_TMPFILE

[Baolin Liu <liubaolin12138@163.com>]

From: Baolin Liu <liubaolin@kylinos.cn>

Allow regular files to be created without a FILE_NAME attribute or
a directory index entry. Keep their on-disk link count at zero and use
d_tmpfile() to attach the inode to the anonymous dentry. Clear the base
inode's in-memory link count before initializing EAs so that attribute
inodes inherit zero links and can be evicted rather than pinning an
unpublished file in cache.

Allow the first hard link of a zero-link inode only when the VFS marks
it I_LINKABLE. Existing deletion checks remain in place, and the VFS
controls O_EXCL and clears I_LINKABLE after publication. Reuse the
zero-link eviction path for unpublished files.

Document the interface and the named-stream restriction before
publication.

Signed-off-by: Baolin Liu <liubaolin@kylinos.cn>
---
Tested the complete five-patch series in QEMU (x86-64, four CPUs, NTFS
debug and lockdep enabled) on disposable NTFS images. Checked anonymous
creation, last-reference cleanup, O_EXCL, linkat publication and failed
publication retry, ACLs, nonresident EAs, prepared timestamps, direct I/O,
mmap, fallocate, truncation, permissions and idmapped mounts. Named-stream
writes were rejected before publication; stream writes, reads and removal
worked after publication.

Verified published file contents, a 12000-byte EA, mode and explicitly set
atime/mtime after cache eviction, read-only and read-write remounts,
unmount/mount and a fresh boot. The inherited access ACL remained readable
in those checks.

Created 400 files using four worker threads, including 100 publications.
Also checked concurrent publication of the same inode, competing target
names, last-unlink races and ENOSPC followed by space reuse. Injected
ENOSPC at five sites in creation, publication and final-open paths and
checked the failure behavior. Offline inspection found the recorded base
MFT records' in-use flags and MFT bitmap bits clear after cleanup.

 Documentation/filesystems/ntfs.rst | 15 +++++++++
 fs/ntfs/namei.c                    | 54 ++++++++++++++++++++++++++----
 2 files changed, 63 insertions(+), 6 deletions(-)

diff --git a/Documentation/filesystems/ntfs.rst b/Documentation/filesystems/ntfs.rst
index 699e91f..a0acc01 100644
--- a/Documentation/filesystems/ntfs.rst
+++ b/Documentation/filesystems/ntfs.rst
@@ -10,6 +10,7 @@ The Linux NTFS filesystem driver
    - Overview
    - Utilities support
    - Linux file attributes
+   - Temporary files
    - Supported mount options
 
 
@@ -58,6 +59,20 @@ These Linux flags are enforced by Linux. Storing them in an NTFS EA does
 not make Windows enforce immutable, append-only or nodump semantics.
 
 
+Temporary files
+===============
+
+The driver supports ``O_TMPFILE`` for regular files. The file has no
+directory entry until it is linked with linkat(2); ``O_EXCL`` prevents
+this publication. Ownership and mode follow normal file creation rules.
+With ACLs enabled, the file's access ACL is derived from the creation
+directory's default ACL. Unpublished files are reclaimed when their last
+reference is released.
+
+Named stream ioctls cannot create or open streams on an unpublished
+temporary file. They can be used after the file has been linked.
+
+
 Supported mount options
 =======================
 
diff --git a/fs/ntfs/namei.c b/fs/ntfs/namei.c
index b26fd9c..4f58b80 100644
--- a/fs/ntfs/namei.c
+++ b/fs/ntfs/namei.c
@@ -489,9 +489,11 @@ static struct ntfs_inode *__ntfs_create(struct mnt_idmap *idmap, struct inode *d
 	simple_inode_init_ts(vi);
 	ni->i_crtime = inode_get_ctime(vi);
 
-	inode_set_mtime_to_ts(dir, ni->i_crtime);
-	inode_set_ctime_to_ts(dir, ni->i_crtime);
-	mark_inode_dirty(dir);
+	if (name) {
+		inode_set_mtime_to_ts(dir, ni->i_crtime);
+		inode_set_ctime_to_ts(dir, ni->i_crtime);
+		mark_inode_dirty(dir);
+	}
 
 	err = ntfs_mft_record_alloc(dir_ni->vol, mode, &ni, NULL,
 			&ni_mrec, -1);
@@ -513,6 +515,10 @@ static struct ntfs_inode *__ntfs_create(struct mnt_idmap *idmap, struct inode *d
 	inode_set_iversion(vi, 1);
 	insert_inode_hash(vi);
 
+	/* Attribute inodes must not pin an unpublished file in cache. */
+	if (!name)
+		clear_nlink(vi);
+
 	mutex_lock_nested(&ni->mrec_lock, NTFS_INODE_MUTEX_NORMAL);
 	mutex_lock_nested(&dir_ni->mrec_lock, NTFS_INODE_MUTEX_PARENT);
 	if (NInoBeingDeleted(dir_ni)) {
@@ -658,6 +664,12 @@ static struct ntfs_inode *__ntfs_create(struct mnt_idmap *idmap, struct inode *d
 	if (err)
 		goto err_out;
 
+	if (!name) {
+		ni_mrec->link_count = 0;
+		mark_mft_record_dirty(ni);
+		goto done;
+	}
+
 	/* Create FILE_NAME attribute. */
 	fn_len = sizeof(struct file_name_attr) + name_len * sizeof(__le16);
 	fn = kzalloc(fn_len, GFP_NOFS);
@@ -709,12 +721,13 @@ static struct ntfs_inode *__ntfs_create(struct mnt_idmap *idmap, struct inode *d
 		goto err_out;
 	}
 
+	ni->flags = fn->file_attributes |
+		    (ni->flags & FILE_ATTRIBUTE_RECALL_ON_OPEN);
+done:
 	unmap_mft_record(ni);
 	mutex_unlock(&dir_ni->mrec_lock);
 	mutex_unlock(&ni->mrec_lock);
 
-	ni->flags = fn->file_attributes |
-		    (ni->flags & FILE_ATTRIBUTE_RECALL_ON_OPEN);
 	/* Set the sequence number. */
 	vi->i_generation = ni->seq_no;
 	set_nlink(vi, 1);
@@ -782,6 +795,8 @@ err_out:
 	mutex_unlock(&dir_ni->mrec_lock);
 	mutex_unlock(&ni->mrec_lock);
 
+	/* The MFT record has already been freed above. */
+	set_nlink(vi, 1);
 	if (rollback_ea_vi)
 		iput(rollback_ea_vi);
 	if (rollback_eai_vi)
@@ -856,6 +871,31 @@ out_free_stream_names:
 	return 0;
 }
 
+static int ntfs_tmpfile(struct mnt_idmap *idmap, struct inode *dir,
+			struct file *file, umode_t mode)
+{
+	struct ntfs_volume *vol = NTFS_SB(dir->i_sb);
+	struct ntfs_inode *ni;
+	struct inode *inode;
+	int err;
+
+	if (NVolShutdown(vol))
+		return -EIO;
+
+	err = ntfs_set_volume_flags(vol, VOLUME_IS_DIRTY);
+	if (err)
+		return err;
+
+	ni = __ntfs_create(idmap, dir, NULL, 0, mode, 0, NULL, 0);
+	if (IS_ERR(ni))
+		return PTR_ERR(ni);
+
+	inode = VFS_I(ni);
+	d_tmpfile(file, inode);
+	unlock_new_inode(inode);
+	return finish_open_simple(file, 0);
+}
+
 static int ntfs_check_unlinkable_dir(struct ntfs_attr_search_ctx *ctx, struct file_name_attr *fn)
 {
 	int link_count;
@@ -1270,7 +1310,8 @@ static int __ntfs_link(struct ntfs_inode *ni, struct ntfs_inode *dir_ni,
 		goto err_out;
 	}
 
-	if (le16_to_cpu(ni_mrec->link_count) == 0) {
+	if (!ni_mrec->link_count &&
+	    !(inode_state_read_once(vi) & I_LINKABLE)) {
 		err = -ENOENT;
 		goto err_out;
 	}
@@ -1703,6 +1744,7 @@ out:
 const struct inode_operations ntfs_dir_inode_ops = {
 	.lookup		= ntfs_lookup,	/* VFS: Lookup directory. */
 	.create		= ntfs_create,
+	.tmpfile	= ntfs_tmpfile,
 	.unlink		= ntfs_unlink,
 	.mkdir		= ntfs_mkdir,
 	.rmdir		= ntfs_rmdir,