[PATCH v9 17/31] fsnotify: Support FS_ERROR event type

[Gabriel Krisman Bertazi <krisman@collabora.com>]

Expose a new type of fsnotify event for filesystems to report errors for
userspace monitoring tools.  fanotify will send this type of
notification for FAN_FS_ERROR events.  This also introduce a helper for
generating the new event.

Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>

---
Changes since v6:
  - Add fsnotify_data_error_report

Changes since v5:
  - pass sb inside data field (jan)
Changes since v3:
  - Squash patch ("fsnotify: Introduce helpers to send error_events")
  - Drop reviewed-bys!

Changes since v2:
  - FAN_ERROR->FAN_FS_ERROR (Amir)

Changes since v1:
  - Overload FS_ERROR with FS_IN_IGNORED
  - Implement support for this type on fsnotify_data_inode (Amir)
---
 include/linux/fsnotify.h         | 13 +++++++++++++
 include/linux/fsnotify_backend.h | 32 +++++++++++++++++++++++++++++++-
 2 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h
index 1e5f7435a4b5..787545e87eeb 100644
--- a/include/linux/fsnotify.h
+++ b/include/linux/fsnotify.h
@@ -339,4 +339,17 @@ static inline void fsnotify_change(struct dentry *dentry, unsigned int ia_valid)
 		fsnotify_dentry(dentry, mask);
 }
 
+static inline int fsnotify_sb_error(struct super_block *sb, struct inode *inode,
+				    int error)
+{
+	struct fs_error_report report = {
+		.error = error,
+		.inode = inode,
+		.sb = sb,
+	};
+
+	return fsnotify(FS_ERROR, &report, FSNOTIFY_EVENT_ERROR,
+			NULL, NULL, NULL, 0);
+}
+
 #endif	/* _LINUX_FS_NOTIFY_H */
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 3a7c31436182..00dbaafbcf95 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -42,6 +42,12 @@
 
 #define FS_UNMOUNT		0x00002000	/* inode on umount fs */
 #define FS_Q_OVERFLOW		0x00004000	/* Event queued overflowed */
+#define FS_ERROR		0x00008000	/* Filesystem Error (fanotify) */
+
+/*
+ * FS_IN_IGNORED overloads FS_ERROR.  It is only used internally by inotify
+ * which does not support FS_ERROR.
+ */
 #define FS_IN_IGNORED		0x00008000	/* last inotify event here */
 
 #define FS_OPEN_PERM		0x00010000	/* open event in an permission hook */
@@ -95,7 +101,8 @@
 #define ALL_FSNOTIFY_EVENTS (ALL_FSNOTIFY_DIRENT_EVENTS | \
 			     FS_EVENTS_POSS_ON_CHILD | \
 			     FS_DELETE_SELF | FS_MOVE_SELF | FS_DN_RENAME | \
-			     FS_UNMOUNT | FS_Q_OVERFLOW | FS_IN_IGNORED)
+			     FS_UNMOUNT | FS_Q_OVERFLOW | FS_IN_IGNORED | \
+			     FS_ERROR)
 
 /* Extra flags that may be reported with event or control handling of events */
 #define ALL_FSNOTIFY_FLAGS  (FS_EXCL_UNLINK | FS_ISDIR | FS_IN_ONESHOT | \
@@ -250,6 +257,13 @@ enum fsnotify_data_type {
 	FSNOTIFY_EVENT_PATH,
 	FSNOTIFY_EVENT_INODE,
 	FSNOTIFY_EVENT_DENTRY,
+	FSNOTIFY_EVENT_ERROR,
+};
+
+struct fs_error_report {
+	int error;
+	struct inode *inode;
+	struct super_block *sb;
 };
 
 static inline struct inode *fsnotify_data_inode(const void *data, int data_type)
@@ -261,6 +275,8 @@ static inline struct inode *fsnotify_data_inode(const void *data, int data_type)
 		return d_inode(data);
 	case FSNOTIFY_EVENT_PATH:
 		return d_inode(((const struct path *)data)->dentry);
+	case FSNOTIFY_EVENT_ERROR:
+		return ((struct fs_error_report *)data)->inode;
 	default:
 		return NULL;
 	}
@@ -300,6 +316,20 @@ static inline struct super_block *fsnotify_data_sb(const void *data,
 		return ((struct dentry *)data)->d_sb;
 	case FSNOTIFY_EVENT_PATH:
 		return ((const struct path *)data)->dentry->d_sb;
+	case FSNOTIFY_EVENT_ERROR:
+		return ((struct fs_error_report *) data)->sb;
+	default:
+		return NULL;
+	}
+}
+
+static inline struct fs_error_report *fsnotify_data_error_report(
+							const void *data,
+							int data_type)
+{
+	switch (data_type) {
+	case FSNOTIFY_EVENT_ERROR:
+		return (struct fs_error_report *) data;
 	default:
 		return NULL;
 	}
-- 
2.33.0