Hi Jeremy,
On Wed, 9 Nov 2022 10:47:41 -0800, Jeremy Allison via samba-technical wrote:
...
> >So the code change needed is to move the logic in vfs_btrfs.c
> >into vfs_default.c, and change the call in vfs_btrfs.c:btrfs_offload_write_send()
> >to SMB_VFS_NEXT_OFFLOAD_WRITE_SEND() to call the old fallback code
> >inside vfs_default.c (vfswrap_offload_write_send()).
>
> Although looking at the current Linux kernel I find inside:
>
> ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
> struct file *file_out, loff_t pos_out,
> size_t len, unsigned int flags)
> {
>
> https://github.com/torvalds/linux/blob/0adc313c4f20639f7e235b8d6719d96a2024cf91/fs/read_write.c#L1506
>
> /*
> * Try cloning first, this is supported by more file systems, and
> * more efficient if both clone and copy are supported (e.g. NFS).
> */
> if (file_in->f_op->remap_file_range &&
> file_inode(file_in)->i_sb == file_inode(file_out)->i_sb) {
> loff_t cloned;
>
> cloned = file_in->f_op->remap_file_range(file_in, pos_in,
> file_out, pos_out,
> min_t(loff_t, MAX_RW_COUNT, len),
> REMAP_FILE_CAN_SHORTEN);
> if (cloned > 0) {
> ret = cloned;
>
> and looking at the code supporting int ioctl(int dest_fd, FICLONERANGE, struct file_clone_range *arg);
> we have:
>
> loff_t do_clone_file_range(struct file *file_in, loff_t pos_in,
> struct file *file_out, loff_t pos_out,
> loff_t len, unsigned int remap_flags)
> ...
> ret = file_in->f_op->remap_file_range(file_in, pos_in,
> file_out, pos_out, len, remap_flags);
>
> So it *looks* like the copy_file_range() syscall will internally
> call the equivalent of FICLONERANGE if the underlying file
> system supports it.
>
> So maybe the right fix is to remove the FICLONERANGE specific
> code from our vfs_btrfs.c and just always use copy_file_range().
copy_file_range() should be okay for FSCTL_SRV_COPYCHUNK, but I don't
think it's an option for FSCTL_DUP_EXTENTS_TO_FILE, as (IIRC) the latter
explicitly requires block cloning so can't fallback to regular copy.
Cheers, David
