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9p: avoid attaching writeback_fid on mmap with type PRIVATE 

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.

Link: http://lkml.kernel.org/r/20190820100325.10313-1-cgxu519@zoho.com.cn
Signed-off-by: Chengguang Xu <cgxu519@zoho.com.cn>
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
This commit is contained in:
Chengguang Xu 2019-08-20 18:03:25 +08:00 committed by Dominique Martinet
parent 089cf7f6ec
commit c87a37ebd4
1 changed files with 3 additions and 0 deletions
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3
fs/9p/vfs_file.c
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@ -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);