[PATCH 9/9] vfs: intercept fsync on overlay files

Miklos Szeredi
2017-02-17T16:09:38Z

Fsync is really an inode operation (AFAICS) so a doing it on a O_RDONLY
file descriptor should flush any data written through an O_WRONLY file
descriptor for example.

To make this work correctly in case the file is copied up after being
opened for read, intercept the fsync operation, similarly to read_iter and
mmap.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
fs/overlay_util.c | 19 +++++++++++++++++++
include/linux/fs.h | 3 +++
include/linux/overlay_util.h | 2 ++
3 files changed, 24 insertions(+)

diff --git a/fs/overlay_util.c b/fs/overlay_util.c
index 063f8c5719d1..dae9d23b1519 100644
--- a/fs/overlay_util.c
+++ b/fs/overlay_util.c
@@ -37,6 +37,25 @@ ssize_t overlay_read_iter(struct file *file, struct kiocb *kio,
}
EXPORT_SYMBOL(overlay_read_iter);

+int overlay_fsync(struct file *file, loff_t start, loff_t end,
+ int datasync)
+{
+ int ret;
+
+ if (likely(overlay_file_consistent(file)))
+ return file->f_op->fsync(file, start, end, datasync);
+
+ file = filp_clone_open(file);
+ if (IS_ERR(file))
+ return PTR_ERR(file);
+
+ ret = vfs_fsync_range(file, start, end, datasync);
+ fput(file);
+
+ return ret;
+}
+EXPORT_SYMBOL(overlay_fsync);
+
int overlay_mmap(struct file *file, struct vm_area_struct *vma)
{
if (unlikely(!overlay_file_consistent(file))) {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 1293005de2e3..1cfa3b33659c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1748,6 +1748,9 @@ static inline int call_mmap(struct file *file, struct vm_area_struct *vma)
static inline int call_fsync(struct file *file, loff_t start, loff_t end,
int datasync)
{
+ if (unlikely(is_overlay_file(file)))
+ return overlay_fsync(file, start, end, datasync);
+
return file->f_op->fsync(file, start, end, datasync);
}

diff --git a/include/linux/overlay_util.h b/include/linux/overlay_util.h
index 2cd66bc316cc..06a0dd923404 100644
--- a/include/linux/overlay_util.h
+++ b/include/linux/overlay_util.h
@@ -11,5 +11,7 @@ struct vm_area_struct;
extern ssize_t overlay_read_iter(struct file *file, struct kiocb *kio,
struct iov_iter *iter);
extern int overlay_mmap(struct file *file, struct vm_area_struct *vma);
+extern int overlay_fsync(struct file *file, loff_t start, loff_t end,
+ int datasync);

#endif /* _LINUX_OVERLAY_FS_H */
--
2.5.5