From a17860e0173e0e9c0ed374e64dc4d5209dfb0757 Mon Sep 17 00:00:00 2001 From: Erez Zadok Date: Thu, 15 May 2014 01:11:22 -0400 Subject: [PATCH] Unionfs: implement vm_ops->page_mkwrite Some file systems (e.g., ext4) require it. Reported by Ted Ts'o. Signed-off-by: Erez Zadok --- fs/unionfs/mmap.c | 36 ++++++++++++++++++++++++++++++++++++ 1 file changed, 36 insertions(+) diff --git a/fs/unionfs/mmap.c b/fs/unionfs/mmap.c index 28b6ce8c0a9..488a582d80e 100644 --- a/fs/unionfs/mmap.c +++ b/fs/unionfs/mmap.c @@ -65,6 +65,41 @@ static int unionfs_fault(struct vm_area_struct *vma, struct vm_fault *vmf) return err; } +static int unionfs_page_mkwrite(struct vm_area_struct *vma, + struct vm_fault *vmf) +{ + int err = 0; + struct file *file, *lower_file; + const struct vm_operations_struct *lower_vm_ops; + struct vm_area_struct lower_vma; + + BUG_ON(!vma); + memcpy(&lower_vma, vma, sizeof(struct vm_area_struct)); + file = lower_vma.vm_file; + lower_vm_ops = UNIONFS_F(file)->lower_vm_ops; + BUG_ON(!lower_vm_ops); + if (!lower_vm_ops->page_mkwrite) + goto out; + + lower_file = unionfs_lower_file(file); + BUG_ON(!lower_file); + /* + * XXX: vm_ops->page_mkwrite may be called in parallel. + * Because we have to resort to temporarily changing the + * vma->vm_file to point to the lower file, a concurrent + * invocation of unionfs_page_mkwrite could see a different + * value. In this workaround, we keep a different copy of the + * vma structure in our stack, so we never expose a different + * value of the vma->vm_file called to us, even temporarily. + * A better fix would be to change the calling semantics of + * ->page_mkwrite to take an explicit file pointer. + */ + lower_vma.vm_file = lower_file; + err = lower_vm_ops->page_mkwrite(&lower_vma, vmf); +out: + return err; +} + /* * XXX: the default address_space_ops for unionfs is empty. We cannot set * our inode->i_mapping->a_ops to NULL because too many code paths expect @@ -86,4 +121,5 @@ struct address_space_operations unionfs_dummy_aops = { struct vm_operations_struct unionfs_vm_ops = { .fault = unionfs_fault, + .page_mkwrite = unionfs_page_mkwrite, }; -- 2.34.1