On Wed 23-08-17 11:43:49, Christoph Hellwig wrote:

On Thu, Aug 17, 2017 at 06:08:12PM +0200, Jan Kara wrote:

quoted

Pretty crude for now...

Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/ext4/file.c                  | 2 ++
 include/linux/mm.h              | 1 +
 include/linux/mman.h            | 3 ++-
 include/uapi/asm-generic/mman.h | 1 +
 mm/mmap.c                       | 5 +++++
 5 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index f84bb29e941e..850037e140d7 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c

@@ -340,6 +340,8 @@ static int ext4_file_mmap(struct file *file, struct vm_area_struct *vma)
 		vma->vm_flags |= VM_MIXEDMAP | VM_HUGEPAGE;
 	} else {
 		vma->vm_ops = &ext4_file_vm_ops;
+		if (vma->vm_flags & VM_SYNC)
+			return -EOPNOTSUPP;
 	}

So each mmap instance would need to reject the flag explicitly?

Or do I misunderstand this VM_SYNC flag?

Yes, if this should be cleaned up, then each mmap instance not supporting
it would need to reject it. However Dan has in his version of mmap()
syscall a mask of supported flags so when I switch to that, it would be
just opt-in. Or I could just reject VM_SYNC for any !IS_DAX inode so then
only ext2 & xfs would need to reject it... But the biggest problem with
this patch is that we need to settle on a safe way of adding new mmap flag.

								Honza
-- 
Jan Kara [off-list ref]
SUSE Labs, CR