Hi, Thanks, applied.
On Thu, Mar 31, 2016 at 04:02:05PM +0300, Denis V. Lunev wrote: > From: Pavel Borzenkov <pborzen...@virtuozzo.com> > > There exist some cases when a client knows that the data it is going to > write is all zeroes. Such cases include mirroring or backing up a device > implemented by a sparse file. > > With current NBD command set, the client has to issue NBD_CMD_WRITE > command with zeroed payload and transfer these zero bytes through the > wire. The server has to write the data onto disk, effectively denying > the sparseness. > > To remedy this, the patch adds WRITE_ZEROES extension with one new > NBD_CMD_WRITE_ZEROES command. > > Signed-off-by: Pavel Borzenkov <pborzen...@virtuozzo.com> > Signed-off-by: Denis V. Lunev <d...@openvz.org> > CC: Wouter Verhelst <w...@uter.be> > CC: Paolo Bonzini <pbonz...@redhat.com> > CC: Kevin Wolf <kw...@redhat.com> > CC: Stefan Hajnoczi <stefa...@redhat.com> > CC: Wouter Verhelst <w...@uter.be> > CC: Alex Bligh <a...@alex.org.uk> > CC: Eric Blake <ebl...@redhat.com> > --- > v2: > - rebased on master > - explicitly state that the client must not set NBD_CMD_WRITE_ZEROES if > support for it wasn't negotiated with the server; > - add new command flag's description in format suitable for moving to > "Command flags" section. > > > doc/proto.md | 64 > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++---- > 1 file changed, 60 insertions(+), 4 deletions(-) > > diff --git a/doc/proto.md b/doc/proto.md > index c1e05c5..a574563 100644 > --- a/doc/proto.md > +++ b/doc/proto.md > @@ -261,6 +261,8 @@ immediately after the handshake flags field in oldstyle > negotiation: > schedule I/O accesses as for a rotational medium > - bit 5, `NBD_FLAG_SEND_TRIM`; should be set to 1 if the server supports > `NBD_CMD_TRIM` commands > +- bit 6, `NBD_FLAG_SEND_WRITE_ZEROES`; should be set to 1 if the server > + supports `NBD_CMD_WRITE_ZEROES` commands > > Clients SHOULD ignore unknown flags. > > @@ -444,10 +446,13 @@ affects a particular command. Clients MUST NOT set a > command flag bit > that is not documented for the particular command; and whether a flag is > valid may depend on negotiation during the handshake phase. > > -- bit 0, `NBD_CMD_FLAG_FUA`; valid during `NBD_CMD_WRITE`. SHOULD be > - set to 1 if the client requires "Force Unit Access" mode of > - operation. MUST NOT be set unless transmission flags included > - `NBD_FLAG_SEND_FUA`. > +- bit 0, `NBD_CMD_FLAG_FUA`; valid during `NBD_CMD_WRITE` and > + `NBD_CMD_WRITE_ZEROES` commands. SHOULD be set to 1 if the client requires > + "Force Unit Access" mode of operation. MUST NOT be set unless transmission > + flags included `NBD_FLAG_SEND_FUA`. > + > +- bit 1, `NBD_CMD_MAY_TRIM`; defined by the experimental `WRITE_ZEROES` > + extension; see below. > > #### Request types > > @@ -523,6 +528,10 @@ The following request types exist: > A client MUST NOT send a trim request unless `NBD_FLAG_SEND_TRIM` > was set in the transmission flags field. > > +* `NBD_CMD_WRITE_ZEROES` (6) > + > + Defined by the experimental `WRITE_ZEROES` extension; see below. > + > * Other requests > > Some third-party implementations may require additional protocol > @@ -654,6 +663,53 @@ option reply type. > message if they do not also send it as a reply to the > `NBD_OPT_SELECT` message. > > +### `WRITE_ZEROES` extension > + > +There exist some cases when a client knows that the data it is going to write > +is all zeroes. Such cases include mirroring or backing up a device > implemented > +by a sparse file. With current NBD command set, the client has to issue > +`NBD_CMD_WRITE` command with zeroed payload and transfer these zero bytes > +through the wire. The server has to write the data onto disk, effectively > +losing the sparseness. > + > +To remedy this, a `WRITE_ZEROES` extension is envisioned. This extension adds > +one new command and one new command flag. > + > +* `NBD_CMD_WRITE_ZEROES` (6) > + > + A write request with no payload. Length and offset define the location > + and amount of data to be zeroed. > + > + The server MUST zero out the data on disk, and then send the reply > + message. The server MAY send the reply message before the data has > + reached permanent storage. > + > + A client MUST NOT send a write zeroes request unless > + `NBD_FLAG_SEND_WRITE_ZEROES` was set in the transmission flags field. > + > + If the `NBD_FLAG_SEND_FUA` flag was set in the transmission flags field, > + the client MAY set the flag `NBD_CMD_FLAG_FUA` in the command flags > field. > + If this flag was set, the server MUST NOT send the reply until it has > + ensured that the newly-zeroed data has reached permanent storage. > + > + If the flag `NBD_CMD_FLAG_MAY_TRIM` was set by the client in the command > + flags field, the server MAY use trimming to zero out the area, but it > + MUST ensure that the data reads back as zero. > + > + If an error occurs, the server SHOULD set the appropriate error code > + in the error field. The server MAY then close the connection. > + > +The server SHOULD return `ENOSPC` if it receives a write zeroes request > +including one or more sectors beyond the size of the device. It SHOULD > +return `EPERM` if it receives a write zeroes request on a read-only export. > + > +The extension adds the following new command flag: > + > +- bit 1, `NBD_CMD_FLAG_MAY_TRIM`; valid during `NBD_CMD_WRITE_ZEROES`. > + SHOULD be set to 1 if the client allows the server to use trim to perform > + the requested operation. The client MAY send `NBD_CMD_FLAG_MAY_TRIM` even > + if `NBD_FLAG_SEND_TRIM` was not set in the transmission flags field. > + > ## About this file > > This file tries to document the NBD protocol as it is currently > -- > 2.1.4 > > > ------------------------------------------------------------------------------ > Transform Data into Opportunity. > Accelerate data analysis in your applications with > Intel Data Analytics Acceleration Library. > Click to learn more. > http://pubads.g.doubleclick.net/gampad/clk?id=278785471&iu=/4140 > _______________________________________________ > Nbd-general mailing list > nbd-gene...@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/nbd-general > -- < ron> I mean, the main *practical* problem with C++, is there's like a dozen people in the world who think they really understand all of its rules, and pretty much all of them are just lying to themselves too. -- #debian-devel, OFTC, 2016-02-12
