Re: [Qemu-devel] [sheepdog] [PATCH v4] sheepdog: selectable object size support

[Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>]

At Tue, 10 Feb 2015 18:35:58 +0800,
Liu Yuan wrote:
> 
> On Tue, Feb 10, 2015 at 06:56:33PM +0900, Teruaki Ishizaki wrote:
> > (2015/02/10 17:58), Liu Yuan wrote:
> > >On Tue, Feb 10, 2015 at 05:22:02PM +0900, Teruaki Ishizaki wrote:
> > >>(2015/02/10 12:10), 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 <ishizaki.teruaki@lab.ntt.co.jp>
> > >>>>---
> > >>>>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   0x18
> > >>>>
> > >>>>  #define SD_FLAG_CMD_WRITE    0x01
> > >>>>  #define SD_FLAG_CMD_COW      0x02
> > >>>>@@ -167,7 +168,8 @@ typedef struct SheepdogVdiReq {
> > >>>>      uint32_t base_vdi_id;
> > >>>>      uint8_t copies;
> > >>>>      uint8_t copy_policy;
> > >>>>-    uint8_t reserved[2];
> > >>>>+    uint8_t store_policy;
> > >>>>+    uint8_t block_size_shift;
> > >>>>      uint32_t snapid;
> > >>>>      uint32_t type;
> > >>>>      uint32_t pad[2];
> > >>>>@@ -186,6 +188,21 @@ typedef struct SheepdogVdiRsp {
> > >>>>      uint32_t pad[5];
> > >>>>  } SheepdogVdiRsp;
> > >>>>
> > >>>>+typedef struct SheepdogClusterRsp {
> > >>>>+    uint8_t proto_ver;
> > >>>>+    uint8_t opcode;
> > >>>>+    uint16_t flags;
> > >>>>+    uint32_t epoch;
> > >>>>+    uint32_t id;
> > >>>>+    uint32_t data_length;
> > >>>>+    uint32_t result;
> > >>>>+    uint8_t nr_copies;
> > >>>>+    uint8_t copy_policy;
> > >>>>+    uint8_t block_size_shift;
> > >>>>+    uint8_t __pad1;
> > >>>>+    uint32_t __pad2[6];
> > >>>>+} SheepdogClusterRsp;
> > >>>>+
> > >>>>  typedef struct SheepdogInode {
> > >>>>      char name[SD_MAX_VDI_LEN];
> > >>>>      char tag[SD_MAX_VDI_TAG_LEN];
> > >>>>@@ -1544,6 +1561,7 @@ static int do_sd_create(BDRVSheepdogState *s, uint32_t *vdi_id, int snapshot,
> > >>>>      hdr.vdi_size = s->inode.vdi_size;
> > >>>>      hdr.copy_policy = s->inode.copy_policy;
> > >>>>      hdr.copies = s->inode.nr_copies;
> > >>>>+    hdr.block_size_shift = s->inode.block_size_shift;
> > >>>>
> > >>>>      ret = do_req(fd, s->aio_context, (SheepdogReq *)&hdr, buf, &wlen, &rlen);
> > >>>>
> > >>>>@@ -1569,9 +1587,12 @@ static int do_sd_create(BDRVSheepdogState *s, uint32_t *vdi_id, int snapshot,
> > >>>>  static int sd_prealloc(const char *filename, Error **errp)
> > >>>>  {
> > >>>>      BlockDriverState *bs = NULL;
> > >>>>+    BDRVSheepdogState *base = NULL;
> > >>>>+    unsigned long buf_size;
> > >>>>      uint32_t idx, max_idx;
> > >>>>+    uint32_t object_size;
> > >>>>      int64_t vdi_size;
> > >>>>-    void *buf = g_malloc0(SD_DATA_OBJ_SIZE);
> > >>>>+    void *buf = NULL;
> > >>>>      int ret;
> > >>>>
> > >>>>      ret = bdrv_open(&bs, filename, NULL, NULL, BDRV_O_RDWR | BDRV_O_PROTOCOL,
> > >>>>@@ -1585,18 +1606,24 @@ static int sd_prealloc(const char *filename, Error **errp)
> > >>>>          ret = vdi_size;
> > >>>>          goto out;
> > >>>>      }
> > >>>>-    max_idx = DIV_ROUND_UP(vdi_size, SD_DATA_OBJ_SIZE);
> > >>>>+
> > >>>>+    base = bs->opaque;
> > >>>>+    object_size = (UINT32_C(1) << base->inode.block_size_shift);
> > >>>>+    buf_size = MIN(object_size, SD_DATA_OBJ_SIZE);
> > >>>>+    buf = g_malloc0(buf_size);
> > >>>>+
> > >>>>+    max_idx = DIV_ROUND_UP(vdi_size, buf_size);
> > >>>>
> > >>>>      for (idx = 0; idx < max_idx; idx++) {
> > >>>>          /*
> > >>>>           * The created image can be a cloned image, so we need to read
> > >>>>           * a data from the source image.
> > >>>>           */
> > >>>>-        ret = bdrv_pread(bs, idx * SD_DATA_OBJ_SIZE, buf, SD_DATA_OBJ_SIZE);
> > >>>>+        ret = bdrv_pread(bs, idx * buf_size, buf, buf_size);
> > >>>>          if (ret < 0) {
> > >>>>              goto out;
> > >>>>          }
> > >>>>-        ret = bdrv_pwrite(bs, idx * SD_DATA_OBJ_SIZE, buf, SD_DATA_OBJ_SIZE);
> > >>>>+        ret = bdrv_pwrite(bs, idx * buf_size, buf, buf_size);
> > >>>>          if (ret < 0) {
> > >>>>              goto out;
> > >>>>          }
> > >>>>@@ -1669,6 +1696,21 @@ static int parse_redundancy(BDRVSheepdogState *s, const char *opt)
> > >>>>      return 0;
> > >>>>  }
> > >>>>
> > >>>>+static int parse_block_size_shift(BDRVSheepdogState *s, QemuOpts *opt)
> > >>>>+{
> > >>>>+    struct SheepdogInode *inode = &s->inode;
> > >>>>+    inode->block_size_shift =
> > >>>>+        (uint8_t)qemu_opt_get_number_del(opt, "block_size_shift", 0);
> > >>>>+    if (inode->block_size_shift == 0) {
> > >>>>+        /* block_size_shift is set for cluster default value by sheepdog */
> > >>>>+        return 0;
> > >>>>+    } else if (inode->block_size_shift < 20 || inode->block_size_shift > 31) {
> > >>>>+        return -EINVAL;
> > >>>>+    }
> > >>>>+
> > >>>>+    return 0;
> > >>>>+}
> > >>>>+
> > >>>>  static int sd_create(const char *filename, QemuOpts *opts,
> > >>>>                       Error **errp)
> > >>>>  {
> > >>>>@@ -1679,6 +1721,7 @@ static int sd_create(const char *filename, QemuOpts *opts,
> > >>>>      BDRVSheepdogState *s;
> > >>>>      char tag[SD_MAX_VDI_TAG_LEN];
> > >>>>      uint32_t snapid;
> > >>>>+    uint64_t max_vdi_size;
> > >>>>      bool prealloc = false;
> > >>>>
> > >>>>      s = g_new0(BDRVSheepdogState, 1);
> > >>>>@@ -1718,9 +1761,10 @@ static int sd_create(const char *filename, QemuOpts *opts,
> > >>>>          }
> > >>>>      }
> > >>>>
> > >>>>-    if (s->inode.vdi_size > SD_MAX_VDI_SIZE) {
> > >>>>-        error_setg(errp, "too big image size");
> > >>>>-        ret = -EINVAL;
> > >>>>+    ret = parse_block_size_shift(s, opts);
> > >>>>+    if (ret < 0) {
> > >>>>+        error_setg(errp, "Invalid block_size_shift:"
> > >>>>+                         " '%s'. please use 20-31", buf);
> > >>>>          goto out;
> > >>>>      }
> > >>>>
> > >>>>@@ -1757,6 +1801,47 @@ static int sd_create(const char *filename, QemuOpts *opts,
> > >>>>      }
> > >>>>
> > >>>>      s->aio_context = qemu_get_aio_context();
> > >>>>+
> > >>>>+    /* if block_size_shift is not specified, get cluster default value */
> > >>>>+    if (s->inode.block_size_shift == 0) {
> > >>>
> > >>>Seems that we don't keep backward compatibility for new QEMU and old sheep that
> > >>>doesn't support SD_OP_GET_CLUSTER_DEFAULT.
> > >>Then, I'll add the operation that if block_size_shift from
> > >>SD_OP_GET_CLUSTER_DEFAULT is zero, block_size_shift is set to 22.
> > >>Is it OK?
> > >
> > >If sheep doesn't support SD_OP_GET_CLUSTER_DEFAULT, sheep will return
> > >SD_RES_INVALID_PARMS. So to keep backward compatibility, we shouldn't issue
> > >SD_OP_GET_CLUSTER_DEFAULT to sheep daemon.
> > OK, I think that the way is better.
> > >
> > >My point is that, after user upgrading the sheep and still stick with old QEMU,
> > >(I guess many users will), any operations in the past sholudn't fail right after
> > >upgrading.
> > >
> > >>
> > >>>
> > >>>What will happen if old QEMU with new sheep that support block_size_shift? Most
> > >>>distributions will ship the old stable qemu that wouldn't be aware of
> > >>>block_size_shift.
> > >>If old QEMU with new sheep is used, VDI is created with cluster default
> > >>block_size_shift and accessed as 4MB object_size.
> > >>So I think that for backward compatibility, users must do cluster
> > >>format command with default block_size_shift 22 equal to
> > >>4MB object_size.
> > >
> > >how old QEMU know about block_size_shift? For old QEMU, block_size_shift is
> > >encoded as 0 and then send the create request to sheep. Does sheep can handle
> > >block_size_shift = 0? You know, we can't pass any value to old QEMU for
> > >block_size_shift.
> > Sheep can handle block_size_shift = 0, when users create new VDI.
> > Old QEMU does do_sd_create() without setting hdr.block_size_shift and
> > sends a request SD_OP_NEW_VDI.
> > If block_size_shift is set to zero, new sheep sets cluster default value
> > in cluster_new_vdi() like copies and copy_policy.
> 
> Okay, so new sheep can handle old QEMU request. By the way, how about the
> suggestion in my last email? (x + 1) * 4MB stuff...

I think specifying object size in multiple of 4MB is overkill. Because
we can specify both of block_size_shift and a number of objects which
belong to VDI. More precisely,
2 ^ block_size_shift * #objects = VDI size
we can choose the block_size_shift between 20 and 30, and #objects
from 1 < 2 ^ 20.
# #objects is specified via VDI size implicitly
The granualarity of VDI sizes seems to be really fine (even
block_size_shift == 30, step is 1GB). So supporting block size with
multiple of 4MB will not provide practical benefit.

Expression of the block size is another topic. I don't have strong
opinion about this.

Thanks,
Hitoshi

> 
> Thanks
> Yuan
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