On Mon, Aug 24, 2020 at 09:57:55PM +0200, David Sterba wrote: > On Fri, Aug 21, 2020 at 12:39:50AM -0700, Omar Sandoval wrote: > > Protocol Updates > > ================ > > > > This series makes some changes to the send stream protocol beyond adding > > the encoded write command/attributes and bumping the version. Namely, v1 > > has a 64k limit on the size of a write due to the 16-bit attribute > > length. This is not enough for encoded writes, as compressed extents may > > be up to 128k and cannot be split up. To address this, the > > BTRFS_SEND_A_DATA is treated specially in v2: its length is implicitly > > the remaining length of the command (which has a 32-bit length). This > > was the last bad of the options I considered. > > > > There are other commands that we've been wanting to add to the protocol: > > fallocate and FS_IOC_SETFLAGS. This series reserves their command and > > attribute numbers but does not implement kernel support for emitting > > them. However, it does implement support in receive for them, so the > > kernel can start emitting those whenever we get around to implementing > > them. > > Can you please outline the protocol changes (as a bullet list) and > eventually cross-ref with items > https://btrfs.wiki.kernel.org/index.php/Design_notes_on_Send/Receive#Send_stream_v2_draft > > I'd like to know which and why you did not implement. The decision here > is between get v2 out with most desired options and rev v3 later with > the rest, or do v2 as complete as possible. The short version is that I didn't implement the kernel side of any of those :) the RWF_ENCODED series + this series is already big, and I didn't want to make it even bigger. I figured updating the protocol/receive now and doing the kernel side later was a good compromise (rather than doing a huge code dump or constantly bumping the protocol version). Is there some reason you don't like this approach? I'm of course happy to go about this in whatever way you think is best. Here's a breakdown of the list from the wiki: * Send extent holes, send preallocated extents: both require fallocate. Boris implemented the receive side. I have some old patches implementing the send side [1], but they're a largish rework of extent tracking in send. * Extent clones within one file: as far as I can tell, this is already possible with v1, it just sends redundant file paths. * Send otime for inodes: the consensus when I posted patches to enable this [2] was that we don't want this after all. * Send file flags (FS_IOC_GETFLAGS/FS_IOC_SETFLAGS): again, Boris implemented the receive side. I previously took a stab at the send side, but it's really annoying because of all of the interactions between directory inheritance, writes vs. NOCOW/append-only/immutable, etc. It's do-able, it would just take a lot of care. * Optionally send owner/group as strings: this one I wasn't aware of. * "block device is not sent over the stream": I don't know what this is referring to. It looks like we send block device nodes with mknod. In my opinion, fallocate support is the most important, SETFLAGS would be good but is a lot of effort, and the rest are nice-to-have. Let me know how you'd like me to go about this. 1: https://github.com/osandov/linux/commits/btrfs-send-v2 2: https://lore.kernel.org/linux-btrfs/cover.1550136164.git.osandov@xxxxxx/
