On Wed, May 15, 2013 at 12:50:13PM -0500, Steve French wrote:
> Doesn't the new syscall have to invalidate the page cache pages that
> the server is about to overwrite as btrfs does with the following line
> in fs/btrfs/ioctl.c
>
> truncate_inode_pages_range(&inode->i_data, destoff,
> PAGE_CACHE_ALIGN(destoff + len) - 1);
The file_operations ->copy_range implementation is responsible for this,
yeah, similar to ->write being responsible for invalidating around
O_DIRECT writes.
> (and doesn't truncate_inode_pages_range handle page cache alignment
> anyway
No, it bugs if given an end offset that isn't page aligned:
BUG_ON((lend & (PAGE_CACHE_SIZE - 1)) != (PAGE_CACHE_SIZE - 1));
Lukas is working on a patch series to fix this:
http://marc.info/?l=linux-fsdevel&m=136854986101843&w=2
> - and also why did btrfs use truncate_inode_pages_range instead
> of invalidate?)
I'm not sure. Maybe they can have racing dirty pages and want them
thrown away rather than having invalidation fail?
> Does nfs client ever have the case where two different superblocks map
> to the same nfs export (and thus the check below is restricting the
> ability to do server side copy)?
>
> + if (inode_in->i_sb != inode_out->i_sb ||
> + file_in->f_path.mnt != file_out->f_path.mnt)
> + return -EXDEV;
Ah, yes, thanks for bringing this up. This check was brought over from
the btrfs ioctl code into the core just to make our lives less
complicated in the short term.
We may well want to push this test down into the ->copy_range methods so
that some can support these cross-sb/mnt copies. I'm not sure how the
nfs client manages all these relationships, but yes, what you suggest
seems plausible.
There's also the long term possibility of using the nfs copy op to
offload copying between files on different servers. The spec talks
about this quite a bit (how the client informs both servers, whether to
use nfs between the servers or some server-specific protocol), but this
certainly isn't my priority.
I figure we can worry about this once we have a ->copy_range method that
can copy files like this safely and are stopped by the test. It's easy
enough to move the test around.
> I am working on cifs client patches for the ioctl, and the new syscall
> also looks pretty easy. Some popular cifs servers (like Windows)
> have supported smb/cifs copy offload for many, many years - and now
> Samba with the support that David Disseldorp added for the clone range
> ioctl has been supporting copychunk (server side copy from Windows to
> Samba) so about time to finish the cifs client equivalent.
Cool, let me know if anything strange pops up.
- z
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