Re: [PATCH v6 17/21] fanotify: Report fid info for file related file system errors

Plumb the pieces to add a FID report to error records.  Since all error
event memory must be pre-allocated, we estimate a file handle size and
if it is insuficient, we report an invalid FID and increase the
prediction for the next error slot allocation.

For errors that don't expose a file handle report it with an invalid
FID.

Signed-off-by: Gabriel Krisman Bertazi <redacted>

---
Changes since v5:
  - Use preallocated MAX_HANDLE_SZ FH buffer
  - Report superblock errors with a zerolength INVALID FID (jan, amir)
---
 fs/notify/fanotify/fanotify.c      | 15 +++++++++++++++
 fs/notify/fanotify/fanotify.h      | 11 +++++++++++
 fs/notify/fanotify/fanotify_user.c |  7 +++++++
 3 files changed, 33 insertions(+)

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 0c7667d3f5d1..f5c16ac37835 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c

@@ -734,6 +734,8 @@ static int fanotify_handle_error_event(struct fsnotify_iter_info *iter_info,
        struct fanotify_sb_mark *sb_mark =
                FANOTIFY_SB_MARK(fsnotify_iter_sb_mark(iter_info));
        struct fanotify_error_event *fee = sb_mark->fee_slot;
+       struct inode *inode = report->inode;
+       int fh_len;

        spin_lock(&group->notification_lock);
        if (fee->err_count++) {

@@ -743,6 +745,19 @@ static int fanotify_handle_error_event(struct fsnotify_iter_info *iter_info,
        spin_unlock(&group->notification_lock);

        fee->fae.type = FANOTIFY_EVENT_TYPE_FS_ERROR;
+       fee->fsid = fee->sb_mark->fsn_mark.connector->fsid;
+
+       fh_len = fanotify_encode_fh_len(inode);
+       if (WARN_ON(fh_len > MAX_HANDLE_SZ)) {
+               /*
+                * Fallback to reporting the error against the super
+                * block.  It should never happen.
+                */
+               inode = NULL;
+               fh_len = fanotify_encode_fh_len(NULL);
+       }
+
+       fanotify_encode_fh(&fee->object_fh, inode, fh_len, NULL, 0);

        if (fsnotify_insert_event(group, &fee->fae.fse,
                                  NULL, fanotify_insert_error_event)) {

diff --git a/fs/notify/fanotify/fanotify.h b/fs/notify/fanotify/fanotify.h
index eeb4a85af74e..158cf0c4b0bd 100644
--- a/fs/notify/fanotify/fanotify.h
+++ b/fs/notify/fanotify/fanotify.h

@@ -223,6 +223,13 @@ struct fanotify_error_event {
        u32 err_count; /* Suppressed errors count */

        struct fanotify_sb_mark *sb_mark; /* Back reference to the mark. */
+
+       __kernel_fsid_t fsid; /* FSID this error refers to. */
+
+       /* object_fh must be followed by the inline handle buffer. */
+       struct fanotify_fh object_fh;
+       /* Reserve space in object_fh.buf[] - access with fanotify_fh_buf() */
+       unsigned char _inline_fh_buf[MAX_HANDLE_SZ];
 };

 static inline struct fanotify_error_event *

@@ -237,6 +244,8 @@ static inline __kernel_fsid_t *fanotify_event_fsid(struct fanotify_event *event)
                return &FANOTIFY_FE(event)->fsid;
        else if (event->type == FANOTIFY_EVENT_TYPE_FID_NAME)
                return &FANOTIFY_NE(event)->fsid;
+       else if (event->type == FANOTIFY_EVENT_TYPE_FS_ERROR)
+               return &FANOTIFY_EE(event)->fsid;
        else
                return NULL;
 }

@@ -248,6 +257,8 @@ static inline struct fanotify_fh *fanotify_event_object_fh(
                return &FANOTIFY_FE(event)->object_fh;
        else if (event->type == FANOTIFY_EVENT_TYPE_FID_NAME)
                return fanotify_info_file_fh(&FANOTIFY_NE(event)->info);
+       else if (event->type == FANOTIFY_EVENT_TYPE_FS_ERROR)
+               return &FANOTIFY_EE(event)->object_fh;
        else
                return NULL;
 }

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 3fff0c994dc8..1ab8f9d8b3ac 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c

@@ -177,6 +177,13 @@ static struct fanotify_event *fanotify_dup_error_to_stack(
        error_on_stack->err_count = fee->err_count;
        error_on_stack->sb_mark = fee->sb_mark;

+       error_on_stack->fsid = fee->fsid;
+
+       memcpy(&error_on_stack->object_fh, &fee->object_fh,
+              sizeof(fee->object_fh));
+       memcpy(error_on_stack->object_fh.buf, fee->object_fh.buf,
+               fee->object_fh.len);
+