fuse: add more control over cache invalidation behaviour

jira SECO-478
RFBugFix: FUSE
commit-author Luis Henriques <luis@igalia.com>
commit 2396356
upstream-diff | conflict in fs/fuse/dir.c due to missing this piece:
       d701902 - fuse: return correct dentry for ->mkdir
       Which is a part of a larger changeset here that we're not going to
       take: https://lore.kernel.org/all/20250227013949.536172-1-neilb@suse.de/
       | Additionally this bumps the Kernel FUSE API minor version from 41
       to 44.  The interface into via fuse3 currently in Rocky 10.1 is
       limited to API 38 anyways at 3.16.2.
       | There is a build conflict due to a major rewrite of the d_revalidate
       calls which now includes the parent directory being passed.
       5be1fa8 Pass parent directory inode and expected name to ->d_revalidate()
       In this case we can use the dentry->i_sb because we only need the
       superblock for get_fuse_conn_super().

Currently userspace is able to notify the kernel to invalidate the cache
for an inode.  This means that, if all the inodes in a filesystem need to
be invalidated, then userspace needs to iterate through all of them and do
this kernel notification separately.

This patch adds the concept of 'epoch': each fuse connection will have the
current epoch initialized and every new dentry will have it's d_time set to
the current epoch value.  A new operation will then allow userspace to
increment the epoch value.  Every time a dentry is d_revalidate()'ed, it's
epoch is compared with the current connection epoch and invalidated if it's
value is different.

	Signed-off-by: Luis Henriques <luis@igalia.com>
	Tested-by: Laura Promberger <laura.promberger@cern.ch>
	Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
(cherry picked from commit 2396356)
	Signed-off-by: Jonathan Maple <jmaple@ciq.com>

build fix: fuse: add more control over cache invalidation behaviour

Author: PlaidCat

fs/fuse/dev.c

@@ -1887,6 +1887,19 @@ static int fuse_notify_resend(struct fuse_conn *fc)
 	return 0;
 }
 
+/*
+ * Increments the fuse connection epoch.  This will result of dentries from
+ * previous epochs to be invalidated.
+ *
+ * XXX optimization: add call to shrink_dcache_sb()?
+ */
+static int fuse_notify_inc_epoch(struct fuse_conn *fc)
+{
+	atomic_inc(&fc->epoch);
+
+	return 0;
+}
+
 static int fuse_notify(struct fuse_conn *fc, enum fuse_notify_code code,
 		       unsigned int size, struct fuse_copy_state *cs)
 {
@@ -1915,6 +1928,9 @@ static int fuse_notify(struct fuse_conn *fc, enum fuse_notify_code code,
 	case FUSE_NOTIFY_RESEND:
 		return fuse_notify_resend(fc);
 
+	case FUSE_NOTIFY_INC_EPOCH:
+		return fuse_notify_inc_epoch(fc);
+
 	default:
 		fuse_copy_finish(cs);
 		return -EINVAL;

fs/fuse/dir.c

@@ -197,9 +197,14 @@ static int fuse_dentry_revalidate(struct dentry *entry, unsigned int flags)
 	struct inode *inode;
 	struct dentry *parent;
 	struct fuse_mount *fm;
+	struct fuse_conn *fc;
 	struct fuse_inode *fi;
 	int ret;
 
+	fc = get_fuse_conn_super(entry->d_sb);
+	if (entry->d_time < atomic_read(&fc->epoch))
+		goto invalid;
+
 	inode = d_inode_rcu(entry);
 	if (inode && fuse_is_bad(inode))
 		goto invalid;
@@ -415,16 +420,20 @@ int fuse_lookup_name(struct super_block *sb, u64 nodeid, const struct qstr *name
 static struct dentry *fuse_lookup(struct inode *dir, struct dentry *entry,
 				  unsigned int flags)
 {
-	int err;
 	struct fuse_entry_out outarg;
+	struct fuse_conn *fc;
 	struct inode *inode;
 	struct dentry *newent;
+	int err, epoch;
 	bool outarg_valid = true;
 	bool locked;
 
 	if (fuse_is_bad(dir))
 		return ERR_PTR(-EIO);
 
+	fc = get_fuse_conn_super(dir->i_sb);
+	epoch = atomic_read(&fc->epoch);
+
 	locked = fuse_lock_inode(dir);
 	err = fuse_lookup_name(dir->i_sb, get_node_id(dir), &entry->d_name,
 			       &outarg, &inode);
@@ -446,6 +455,7 @@ static struct dentry *fuse_lookup(struct inode *dir, struct dentry *entry,
 		goto out_err;
 
 	entry = newent ? newent : entry;
+	entry->d_time = epoch;
 	if (outarg_valid)
 		fuse_change_entry_timeout(entry, &outarg);
 	else
@@ -618,7 +628,6 @@ static int fuse_create_open(struct mnt_idmap *idmap, struct inode *dir,
 			    struct dentry *entry, struct file *file,
 			    unsigned int flags, umode_t mode, u32 opcode)
 {
-	int err;
 	struct inode *inode;
 	struct fuse_mount *fm = get_fuse_mount(dir);
 	FUSE_ARGS(args);
@@ -628,11 +637,13 @@ static int fuse_create_open(struct mnt_idmap *idmap, struct inode *dir,
 	struct fuse_entry_out outentry;
 	struct fuse_inode *fi;
 	struct fuse_file *ff;
+	int epoch, err;
 	bool trunc = flags & O_TRUNC;
 
 	/* Userspace expects S_IFREG in create mode */
 	BUG_ON((mode & S_IFMT) != S_IFREG);
 
+	epoch = atomic_read(&fm->fc->epoch);
 	forget = fuse_alloc_forget();
 	err = -ENOMEM;
 	if (!forget)
@@ -701,6 +712,7 @@ static int fuse_create_open(struct mnt_idmap *idmap, struct inode *dir,
 	}
 	kfree(forget);
 	d_instantiate(entry, inode);
+	entry->d_time = epoch;
 	fuse_change_entry_timeout(entry, &outentry);
 	fuse_dir_changed(dir);
 	err = generic_file_open(inode, file);
@@ -787,12 +799,14 @@ static int create_new_entry(struct mnt_idmap *idmap, struct fuse_mount *fm,
 	struct fuse_entry_out outarg;
 	struct inode *inode;
 	struct dentry *d;
-	int err;
 	struct fuse_forget_link *forget;
+	int epoch, err;
 
 	if (fuse_is_bad(dir))
 		return -EIO;
 
+	epoch = atomic_read(&fm->fc->epoch);
+
 	forget = fuse_alloc_forget();
 	if (!forget)
 		return -ENOMEM;
@@ -835,9 +849,11 @@ static int create_new_entry(struct mnt_idmap *idmap, struct fuse_mount *fm,
 		return PTR_ERR(d);
 
 	if (d) {
+		d->d_time = epoch;
 		fuse_change_entry_timeout(d, &outarg);
 		dput(d);
 	} else {
+		entry->d_time = epoch;
 		fuse_change_entry_timeout(entry, &outarg);
 	}
 	fuse_dir_changed(dir);

fs/fuse/fuse_i.h

@@ -604,6 +604,9 @@ struct fuse_conn {
 	/** Number of fuse_dev's */
 	atomic_t dev_count;
 
+	/** Current epoch for up-to-date dentries */
+	atomic_t epoch;
+
 	struct rcu_head rcu;
 
 	/** The user id for this mount */

fs/fuse/inode.c

@@ -926,6 +926,7 @@ void fuse_conn_init(struct fuse_conn *fc, struct fuse_mount *fm,
 	init_rwsem(&fc->killsb);
 	refcount_set(&fc->count, 1);
 	atomic_set(&fc->dev_count, 1);
+	atomic_set(&fc->epoch, 1);
 	init_waitqueue_head(&fc->blocked_waitq);
 	fuse_iqueue_init(&fc->iq, fiq_ops, fiq_priv);
 	INIT_LIST_HEAD(&fc->bg_queue);

fs/fuse/readdir.c

@@ -161,6 +161,7 @@ static int fuse_direntplus_link(struct file *file,
 	struct fuse_conn *fc;
 	struct inode *inode;
 	DECLARE_WAIT_QUEUE_HEAD_ONSTACK(wq);
+	int epoch;
 
 	if (!o->nodeid) {
 		/*
@@ -190,6 +191,7 @@ static int fuse_direntplus_link(struct file *file,
 		return -EIO;
 
 	fc = get_fuse_conn(dir);
+	epoch = atomic_read(&fc->epoch);
 
 	name.hash = full_name_hash(parent, name.name, name.len);
 	dentry = d_lookup(parent, &name);
@@ -256,6 +258,7 @@ static int fuse_direntplus_link(struct file *file,
 	}
 	if (fc->readdirplus_auto)
 		set_bit(FUSE_I_INIT_RDPLUS, &get_fuse_inode(inode)->state);
+	dentry->d_time = epoch;
 	fuse_change_entry_timeout(dentry, o);
 
 	dput(dentry);

include/uapi/linux/fuse.h

@@ -220,6 +220,9 @@
  *
  *  7.41
  *  - add FUSE_ALLOW_IDMAP
+ *
+ *  7.44
+ *  - add FUSE_NOTIFY_INC_EPOCH
  */
 
 #ifndef _LINUX_FUSE_H
@@ -255,7 +258,7 @@
 #define FUSE_KERNEL_VERSION 7
 
 /** Minor version number of this interface */
-#define FUSE_KERNEL_MINOR_VERSION 41
+#define FUSE_KERNEL_MINOR_VERSION 44
 
 /** The node ID of the root inode */
 #define FUSE_ROOT_ID 1
@@ -655,6 +658,7 @@ enum fuse_notify_code {
 	FUSE_NOTIFY_RETRIEVE = 5,
 	FUSE_NOTIFY_DELETE = 6,
 	FUSE_NOTIFY_RESEND = 7,
+	FUSE_NOTIFY_INC_EPOCH = 8,
 	FUSE_NOTIFY_CODE_MAX,
 };