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dm: enable request based option

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This patch enables request-based dm.

o Request-based dm and bio-based dm coexist, since there are
  some target drivers which are more fitting to bio-based dm.
  Also, there are other bio-based devices in the kernel
  (e.g. md, loop).
  Since bio-based device can't receive struct request,
  there are some limitations on device stacking between
  bio-based and request-based.

                     type of underlying device
                   bio-based      request-based
   ----------------------------------------------
    bio-based         OK                OK
    request-based     --                OK

  The device type is recognized by the queue flag in the kernel,
  so dm follows that.

o The type of a dm device is decided at the first table binding time.
  Once the type of a dm device is decided, the type can't be changed.

o Mempool allocations are deferred to at the table loading time, since
  mempools for request-based dm are different from those for bio-based
  dm and needed mempool type is fixed by the type of table.

o Currently, request-based dm supports only tables that have a single
  target.  To support multiple targets, we need to support request
  splitting or prevent bio/request from spanning multiple targets.
  The former needs lots of changes in the block layer, and the latter
  needs that all target drivers support merge() function.
  Both will take a time.

Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Kiyoshi Ueda
2009-06-22 10:12:36 +01:00
committed by Alasdair G Kergon
parent cec47e3d4a
commit e6ee8c0b76
4 changed files with 285 additions and 26 deletions
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13
drivers/md/dm-ioctl.c
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@@ -1050,6 +1050,12 @@ static int populate_table(struct dm_table *table,
next = spec->next;
}
r = dm_table_set_type(table);
if (r) {
DMWARN("unable to set table type");
return r;
}
return dm_table_complete(table);
}
@@ -1095,6 +1101,13 @@ static int table_load(struct dm_ioctl *param, size_t param_size)
goto out;
}
r = dm_table_alloc_md_mempools(t);
if (r) {
DMWARN("unable to allocate mempools for this table");
dm_table_destroy(t);
goto out;
}
down_write(&_hash_lock);
hc = dm_get_mdptr(md);
if (!hc || hc->md != md) {