On Wed, Mar 23, 2016 at 05:16:02PM +0300, Denis V. Lunev wrote: > From: Pavel Borzenkov > > With the availability of sparse storage formats, it is often needed to > query status of a particular LBA range and read only those blocks of > data that are actually present on the block device. > > To provide such information, the patch adds GET_LBA_STATUS extension > with one new NBD_CMD_GET_LBA_STATUS command. > > There exists a concept of data dirtiness, which is required during, for > example, incremental block device backup. To express this concept via > NBD protocol, this patch also adds additional mode of operation to > NBD_CMD_GET_LBA_STATUS command. > > Since NBD protocol has no notion of block size, and to mimic SCSI "GET > LBA STATUS" command more closely, it has been chosen to return a list of > extents in the response of NBD_CMD_GET_LBA_STATUS command, instead of a > bitmap. > > Signed-off-by: Pavel Borzenkov > Reviewed-by: Roman Kagan > Signed-off-by: Denis V. Lunev > CC: Wouter Verhelst > CC: Paolo Bonzini > CC: Kevin Wolf > CC: Stefan Hajnoczi > --- > doc/proto.md | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 82 insertions(+) > > diff --git a/doc/proto.md b/doc/proto.md > index cda213c..fff515d 100644 > --- a/doc/proto.md > +++ b/doc/proto.md > @@ -243,6 +243,8 @@ immediately after the global flags field in oldstyle negotiation: > `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 > +- bit 7, `NBD_FLAG_SEND_GET_LBA_STATUS`; should be set to 1 if the server > + supports `NBD_CMD_GET_LBA_STATUS` commands > > ##### Client flags > > @@ -477,6 +479,10 @@ The following request types exist: > > Defined by the experimental `WRITE_ZEROES` extension; see below. > > +* `NBD_CMD_GET_LBA_STATUS` (7) > + > + Defined by the experimental `GET_LBA_STATUS` extension; see below. > + > * Other requests > > Some third-party implementations may require additional protocol > @@ -638,6 +644,82 @@ 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. > > +### `GET_LBA_STATUS` extension > + > +With the availability of sparse storage formats, it is often needed to query > +status of a particular LBA range and read only those blocks of data that are > +actually present on the block device. > + > +Some storage formats and operations over such formats express a concept of > +data dirtiness. Whether the operation is block device mirroring, > +incremental block device backup or any other operation with a concept of > +data dirtiness, they all share a need to provide a list of LBA ranges > +that this particular operation treats as dirty. > + > +To provide such class of information, `GET_LBA_STATUS` extension adds new > +`NBD_CMD_GET_LBA_STATUS` command which returns a list of LBA ranges with > +their respective states. > + > +* `NBD_CMD_GET_LBA_STATUS` (7) > + > + An LBA range status query request. Length and offset define the range > + of interest. The server MUST reply with a reply header, followed > + immediately by the following data: As Eric noted, please expand LBA at least once. > + - 32 bits, length of parameter data that follow (unsigned) > + - zero or more LBA status descriptors, each having the following > + structure: > + > + * 64 bits, offset (unsigned) > + * 32 bits, length (unsigned) > + * 16 bits, status (unsigned) > + > + unless an error condition has occurred. > + > + If an error occurs, the server SHOULD set the appropriate error code > + in the error field. The server MUST then either close the > + connection, or send *length of parameter data* bytes of data > + (which MAY be invalid). > + > + The type of information required by the client is passed to server in the > + command flags field. If the server does not implement requested type or > + have no means to express it, it MUST NOT return an error, but instead MUST > + return a single LBA status descriptor with *offset* and *length* equal to > + the *offset* and *length* from request, and *status* set to `0`. > + > + The following request types are currently defined for the command: > + > + 1. Block provisioning state > + > + Upon receiving an `NBD_CMD_GET_LBA_STATUS` command with command flags > + field set to `NBD_FLAG_GET_ALLOCATED` (0x0), the server MUST return I prefer to have a non-zero flag value. > + the provisioning state of the device. The following provisionnig states > + are defined for the command: > + > + - `NBD_STATE_ALLOCATED` (0x0), LBA extent is present on the block device; > + - `NBD_STATE_ZEROED` (0x1), LBA extent is present on the block device > + and contains zeroes; Presumably this should be "contains only zeroes"? Also, this may end up being a fairly expensive call for the server to process. Is it really useful? > + - `NBD_STATE_DEALLOCATED` (0x2), LBA extent is not present on the > + block device. A client MUST NOT make any assumptions about the > + contents of the extent. > + > + 2. Block dirtiness state > + > + Upon receiving an `NBD_CMD_GET_LBA_STATUS` command with command flags > + field set to `NBD_FLAG_GET_DIRTY` (0x1), the server MUST return > + the dirtiness status of the device. The following dirtiness states > + are defined for the command: > + > + - `NBD_STATE_DIRTY` (0x0), LBA extent is dirty; > + - `NBD_STATE_CLEAN` (0x1), LBA extent is clean. > + > + Generic NBD client implementation without knowledge of a particular NBD > + server operation MUST NOT make any assumption on the meaning of the > + NBD_STATE_DIRTY or NBD_STATE_CLEAN states. That makes it a useless call. A server can read /dev/random to decide whether to send STATE_DIRTY or STATE_CLEAN, and still be compliant with this spec. Either the spec should define what it means for a block to be in a dirty state, or it should not talk about it. -- < 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