eventfs: Implement functions to create files and dirs when accessed

Add create_file() and create_dir() functions to create the files and
directories respectively when they are accessed. The functions will be
called from the lookup operation of the inode_operations or from the open
function of file_operations.

Link: https://lkml.kernel.org/r/1690568452-46553-8-git-send-email-akaher@vmware.com
Signed-off-by: Ajay Kaher <akaher@vmware.com>
Co-developed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Tested-by: Ching-lin Yu <chinglinyu@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index 24d645c..5240bd2 100644 (file)
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -101,7 +101,34 @@ static struct dentry *create_file(const char *name, umode_t mode,
                                  struct dentry *parent, void *data,
                                  const struct file_operations *fop)
 {
-       return NULL;
+       struct tracefs_inode *ti;
+       struct dentry *dentry;
+       struct inode *inode;
+
+       if (!(mode & S_IFMT))
+               mode |= S_IFREG;
+
+       if (WARN_ON_ONCE(!S_ISREG(mode)))
+               return NULL;
+
+       dentry = eventfs_start_creating(name, parent);
+
+       if (IS_ERR(dentry))
+               return dentry;
+
+       inode = tracefs_get_inode(dentry->d_sb);
+       if (unlikely(!inode))
+               return eventfs_failed_creating(dentry);
+
+       inode->i_mode = mode;
+       inode->i_fop = fop;
+       inode->i_private = data;
+
+       ti = get_tracefs(inode);
+       ti->flags |= TRACEFS_EVENT_INODE;
+       d_instantiate(dentry, inode);
+       fsnotify_create(dentry->d_parent->d_inode, dentry);
+       return eventfs_end_creating(dentry);
 };
 
 /**
@@ -123,7 +150,31 @@ static struct dentry *create_file(const char *name, umode_t mode,
  */
 static struct dentry *create_dir(const char *name, struct dentry *parent, void *data)
 {
-       return NULL;
+       struct tracefs_inode *ti;
+       struct dentry *dentry;
+       struct inode *inode;
+
+       dentry = eventfs_start_creating(name, parent);
+       if (IS_ERR(dentry))
+               return dentry;
+
+       inode = tracefs_get_inode(dentry->d_sb);
+       if (unlikely(!inode))
+               return eventfs_failed_creating(dentry);
+
+       inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
+       inode->i_op = &eventfs_root_dir_inode_operations;
+       inode->i_fop = &eventfs_file_operations;
+       inode->i_private = data;
+
+       ti = get_tracefs(inode);
+       ti->flags |= TRACEFS_EVENT_INODE;
+
+       inc_nlink(inode);
+       d_instantiate(dentry, inode);
+       inc_nlink(dentry->d_parent->d_inode);
+       fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
+       return eventfs_end_creating(dentry);
 }
 
 /**
@@ -234,6 +285,12 @@ create_dentry(struct eventfs_file *ef, struct dentry *parent, bool lookup)
        } else {
                /* A race here, should try again (unless freed) */
                invalidate = true;
+
+               /*
+                * Should never happen unless we get here due to being freed.
+                * Otherwise it means two dentries exist with the same name.
+                */
+               WARN_ON_ONCE(!ef->is_freed);
        }
        mutex_unlock(&eventfs_mutex);
        if (invalidate)

diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
index 4acc4b4..d927306 100644 (file)
--- a/fs/tracefs/inode.c
+++ b/fs/tracefs/inode.c
@@ -475,6 +475,80 @@ struct dentry *tracefs_end_creating(struct dentry *dentry)
 }
 
 /**
+ * eventfs_start_creating - start the process of creating a dentry
+ * @name: Name of the file created for the dentry
+ * @parent: The parent dentry where this dentry will be created
+ *
+ * This is a simple helper function for the dynamically created eventfs
+ * files. When the directory of the eventfs files are accessed, their
+ * dentries are created on the fly. This function is used to start that
+ * process.
+ */
+struct dentry *eventfs_start_creating(const char *name, struct dentry *parent)
+{
+       struct dentry *dentry;
+       int error;
+
+       error = simple_pin_fs(&trace_fs_type, &tracefs_mount,
+                             &tracefs_mount_count);
+       if (error)
+               return ERR_PTR(error);
+
+       /*
+        * If the parent is not specified, we create it in the root.
+        * We need the root dentry to do this, which is in the super
+        * block. A pointer to that is in the struct vfsmount that we
+        * have around.
+        */
+       if (!parent)
+               parent = tracefs_mount->mnt_root;
+
+       if (unlikely(IS_DEADDIR(parent->d_inode)))
+               dentry = ERR_PTR(-ENOENT);
+       else
+               dentry = lookup_one_len(name, parent, strlen(name));
+
+       if (!IS_ERR(dentry) && dentry->d_inode) {
+               dput(dentry);
+               dentry = ERR_PTR(-EEXIST);
+       }
+
+       if (IS_ERR(dentry))
+               simple_release_fs(&tracefs_mount, &tracefs_mount_count);
+
+       return dentry;
+}
+
+/**
+ * eventfs_failed_creating - clean up a failed eventfs dentry creation
+ * @dentry: The dentry to clean up
+ *
+ * If after calling eventfs_start_creating(), a failure is detected, the
+ * resources created by eventfs_start_creating() needs to be cleaned up. In
+ * that case, this function should be called to perform that clean up.
+ */
+struct dentry *eventfs_failed_creating(struct dentry *dentry)
+{
+       dput(dentry);
+       simple_release_fs(&tracefs_mount, &tracefs_mount_count);
+       return NULL;
+}
+
+/**
+ * eventfs_end_creating - Finish the process of creating a eventfs dentry
+ * @dentry: The dentry that has successfully been created.
+ *
+ * This function is currently just a place holder to match
+ * eventfs_start_creating(). In case any synchronization needs to be added,
+ * this function will be used to implement that without having to modify
+ * the callers of eventfs_start_creating().
+ */
+struct dentry *eventfs_end_creating(struct dentry *dentry)
+{
+       return dentry;
+}
+
+/**
  * tracefs_create_file - create a file in the tracefs filesystem
  * @name: a pointer to a string containing the name of the file to create.
  * @mode: the permission that the file should have.

diff --git a/fs/tracefs/internal.h b/fs/tracefs/internal.h
index 9bfad9d..69c2b1d 100644 (file)
--- a/fs/tracefs/internal.h
+++ b/fs/tracefs/internal.h
@@ -21,6 +21,9 @@ struct dentry *tracefs_start_creating(const char *name, struct dentry *parent);
 struct dentry *tracefs_end_creating(struct dentry *dentry);
 struct dentry *tracefs_failed_creating(struct dentry *dentry);
 struct inode *tracefs_get_inode(struct super_block *sb);
+struct dentry *eventfs_start_creating(const char *name, struct dentry *parent);
+struct dentry *eventfs_failed_creating(struct dentry *dentry);
+struct dentry *eventfs_end_creating(struct dentry *dentry);
 void eventfs_set_ef_status_free(struct dentry *dentry);
 
 #endif /* _TRACEFS_INTERNAL_H */