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Re: [Qemu-devel] [Nbd] [PATCH 2/2] NBD proto: add GET_LBA_STATUS extensi
From: |
Wouter Verhelst |
Subject: |
Re: [Qemu-devel] [Nbd] [PATCH 2/2] NBD proto: add GET_LBA_STATUS extension |
Date: |
Wed, 23 Mar 2016 18:58:34 +0100 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On Wed, Mar 23, 2016 at 05:16:02PM +0300, Denis V. Lunev wrote:
> From: Pavel Borzenkov <address@hidden>
>
> 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 <address@hidden>
> Reviewed-by: Roman Kagan <address@hidden>
> Signed-off-by: Denis V. Lunev <address@hidden>
> CC: Wouter Verhelst <address@hidden>
> CC: Paolo Bonzini <address@hidden>
> CC: Kevin Wolf <address@hidden>
> CC: Stefan Hajnoczi <address@hidden>
> ---
> 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
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[Qemu-devel] [PATCH 2/2] NBD proto: add GET_LBA_STATUS extension, Denis V. Lunev, 2016/03/23
Re: [Qemu-devel] [Nbd] [PATCH 2/2] NBD proto: add GET_LBA_STATUS extension,
Wouter Verhelst <=
- Re: [Qemu-devel] [Nbd] [PATCH 2/2] NBD proto: add GET_LBA_STATUS extension, Kevin Wolf, 2016/03/23
- Re: [Qemu-devel] [Nbd] [PATCH 2/2] NBD proto: add GET_LBA_STATUS extension, Pavel Borzenkov, 2016/03/24
- Re: [Qemu-devel] [Nbd] [PATCH 2/2] NBD proto: add GET_LBA_STATUS extension, Wouter Verhelst, 2016/03/24
- Re: [Qemu-devel] [Nbd] [PATCH 2/2] NBD proto: add GET_LBA_STATUS extension, Pavel Borzenkov, 2016/03/24
- Re: [Qemu-devel] [Nbd] [PATCH 2/2] NBD proto: add GET_LBA_STATUS extension, Wouter Verhelst, 2016/03/24
Re: [Qemu-devel] [Nbd] [PATCH 2/2] NBD proto: add GET_LBA_STATUS extension, Pavel Borzenkov, 2016/03/24
Re: [Qemu-devel] [Nbd] [PATCH 2/2] NBD proto: add GET_LBA_STATUS extension, Wouter Verhelst, 2016/03/24
Re: [Qemu-devel] [Nbd] [PATCH 2/2] NBD proto: add GET_LBA_STATUS extension, Alex Bligh, 2016/03/24
Re: [Qemu-devel] [Nbd] [PATCH 2/2] NBD proto: add GET_LBA_STATUS extension, Paolo Bonzini, 2016/03/24
Re: [Qemu-devel] [Nbd] [PATCH 2/2] NBD proto: add GET_LBA_STATUS extension, Alex Bligh, 2016/03/24