|
| From: | Teruaki Ishizaki |
| Subject: | Re: [Qemu-devel] [PATCH v4] sheepdog: selectable object size support |
| Date: | Fri, 13 Feb 2015 13:28:10 +0900 |
| User-agent: | Mozilla/5.0 (Windows NT 6.1; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 |
(2015/02/13 11:01), Liu Yuan wrote:
On Fri, Feb 13, 2015 at 10:33:04AM +0900, Teruaki Ishizaki wrote:(2015/02/12 11:55), Liu Yuan wrote:On Thu, Feb 12, 2015 at 11:33:16AM +0900, Teruaki Ishizaki wrote:(2015/02/12 11:19), Liu Yuan wrote:On Thu, Feb 12, 2015 at 10:51:25AM +0900, Teruaki Ishizaki wrote:(2015/02/10 20:12), Liu Yuan wrote:On Tue, Jan 27, 2015 at 05:35:27PM +0900, Teruaki Ishizaki wrote:Previously, qemu block driver of sheepdog used hard-coded VDI object size. This patch enables users to handle "block_size_shift" value for calculating VDI object size. When you start qemu, you don't need to specify additional command option. But when you create the VDI which doesn't have default object size with qemu-img command, you specify block_size_shift option. If you want to create a VDI of 8MB(1 << 23) object size, you need to specify following command option. # qemu-img create -o block_size_shift=23 sheepdog:test1 100M In addition, when you don't specify qemu-img command option, a default value of sheepdog cluster is used for creating VDI. # qemu-img create sheepdog:test2 100M Signed-off-by: Teruaki Ishizaki <address@hidden> --- V4: - Limit a read/write buffer size for creating a preallocated VDI. - Replace a parse function for the block_size_shift option. - Fix an error message. V3: - Delete the needless operation of buffer. - Delete the needless operations of request header. for SD_OP_GET_CLUSTER_DEFAULT. - Fix coding style problems. V2: - Fix coding style problem (white space). - Add members, store_policy and block_size_shift to struct SheepdogVdiReq. - Initialize request header to use block_size_shift specified by user. --- block/sheepdog.c | 138 ++++++++++++++++++++++++++++++++++++++------- include/block/block_int.h | 1 + 2 files changed, 119 insertions(+), 20 deletions(-) diff --git a/block/sheepdog.c b/block/sheepdog.c index be3176f..a43b947 100644 --- a/block/sheepdog.c +++ b/block/sheepdog.c @@ -37,6 +37,7 @@ #define SD_OP_READ_VDIS 0x15 #define SD_OP_FLUSH_VDI 0x16 #define SD_OP_DEL_VDI 0x17 +#define SD_OP_GET_CLUSTER_DEFAULT 0x18This might not be necessary. For old qemu or the qemu-img without setting option, the block_size_shift will be 0. If we make 0 to represent 4MB object, then we don't need to get the default cluster object size. We migth even get rid of the idea of cluster default size. The downsize is that, if we want to create a vdi with different size not the default 4MB, we have to write it every time for qemu-img or dog. If we choose to keep the idea of cluster default size, I think we'd also try to avoid call this request from QEMU to make backward compatibility easier. In this scenario, 0 might be used to ask new sheep to decide to use cluster default size. Both old qemu and new QEMU will send 0 to sheep and both old and new sheep can handle 0 though it has different meanings. Table for this bit as 0: Qe: qemu SD: Sheep daemon CDS: Cluster Default Size Ign: Ignored by the sheep daemon Qe/sd new old new CDS Ign old CDS NULLDoes Ign mean that VDI is handled as 4MB object size?Yes, old sheep can only handle 4MB object and doesn't check this field at all.I think this approach is acceptable. The difference to your patch is that we don't send SD_OP_GET_CLUSTER_DEFAULT to sheep daemon and SD_OP_GET_CLUSTER_DEFAULT can be removed.When users create a new VDI with qemu-img, qemu's Sheepdog backend driver calculates max limit VDI size.But if block_size_shift option is not specified, qemu's Sheepdog backend driver can't calculate max limit VDI size.If block_size_shift not specified, this means 1 for old sheep, use 4MB size 2 for new sheep, use cluster wide default value. And sheep then can calculate it on its own, no?Dog command(client) calculate max size, so I think that qemu's Sheepdog backend driver should calculate it like dog command. Is that policy changeable?I checked the QEMU code and got your idea. In the past it was fixed size so very easy to hardcode the check in the client, no communication with sheep needed. Yes, if it is reasonable, we can change it. I think we can push the size calculation logic into sheep, if not the right size return INVALID_PARAMETER to clients. Clients just check this and report error back to users. There is no backward compability for this approach, since 4MB is the smallest size. OLD QEMU will limit the max_size as 4TB, which is no problem for new sheep.I have checked the Qemu and sheepdog code. When we resize VDI, sd_truncate() is called and resize value is handled by Qemu. (Sorry I haven't noticed this operation) Then, sd_truncate() writes Sheepdog inode object directly. So Sheepdog server can't handle maximum VDI size. As I thought, should we use SD_OP_GET_CLUSTER_DEFAULT? Should maxmimum VDI size be calculated on client program?Based on your description, yes, we have to use it. I'd suggest rename SD_OP_GET_CLUSTER_DEFAULT as SD_OP_GET_DEFAULT_OBJECT_SIZE. If we use it, you need to take care of old sheep that will return INVALID_PARAMETER and handle it.
Now, SD_OP_GET_CLUSTER_DEFAULT can get block_size_shift, copy_policy and copies informations. I think that SD_OP_GET_DEFAULT_OBJECT_SIZE doesn't fit in. I'll change to handle INVALID_PARAMETER. Thanks, Teruaki
| [Prev in Thread] | Current Thread | [Next in Thread] |