On Fri, Jan 27, 2017 at 1:50 PM, Amir Goldstein [off-list ref] wrote:

On Fri, Jan 27, 2017 at 1:09 PM, Miklos Szeredi [off-list ref] wrote:

quoted

On Mon, Jan 23, 2017 at 8:43 PM, Amir Goldstein [off-list ref] wrote:

quoted

Before calling write f_ops, call file_start_write() instead
of sb_start_write().

This ensures freeze protection for both overlay and upper fs
when file is open from an overlayfs mount.

Replace {sb,file}_start_write() for {copy,clone}_file_range() and
for fallocate().

For dedup_file_range() there is no need for mnt_want_write_file().
File is already open for write, so we already have mnt_want_write()
and we only need file_start_write().

Being opened for write is not verified if capable(CAP_SYS_ADMIN).
Ugly special case, don't ask me why it's done...

Christoph, Darrick, is that by design?

Anyway, whether is makes sense or not, that's a legacy from
BTRFS_IOC_FILE_EXTENT_SAME, we probably have to live with.

Michael, I recon man page needs updating.

I'll remove this hunk from the patch.