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Subject[PATCH] 9p: avoid attaching writeback_fid on mmap with type PRIVATE
Date
Currently on mmap cache policy, we always attach writeback_fid
whether mmap type is SHARED or PRIVATE. However, in the use case
of kata-container which combines 9p(Guest OS) with overlayfs(Host OS),
this behavior will trigger overlayfs' copy-up when excute command
inside container.

Signed-off-by: Chengguang Xu <cgxu519@zoho.com.cn>
---
fs/9p/vfs_file.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/fs/9p/vfs_file.c b/fs/9p/vfs_file.c
index 4cc966a31cb3..fe7f0bd2048e 100644
--- a/fs/9p/vfs_file.c
+++ b/fs/9p/vfs_file.c
@@ -513,6 +513,7 @@ v9fs_mmap_file_mmap(struct file *filp, struct vm_area_struct *vma)
v9inode = V9FS_I(inode);
mutex_lock(&v9inode->v_mutex);
if (!v9inode->writeback_fid &&
+ (vma->vm_flags & VM_SHARED) &&
(vma->vm_flags & VM_WRITE)) {
/*
* clone a fid and add it to writeback_fid
@@ -614,6 +615,8 @@ static void v9fs_mmap_vm_close(struct vm_area_struct *vma)
(vma->vm_end - vma->vm_start - 1),
};

+ if (!(vma->vm_flags & VM_SHARED))
+ return;

p9_debug(P9_DEBUG_VFS, "9p VMA close, %p, flushing", vma);

--
2.20.1


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