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Add support for "snapshot-merge" target.

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Introduces new libdevmapper function dm_tree_node_add_snapshot_merge_target

Verifies that the kernel (dm-snapshot) provides the 'snapshot-merge'
target.

Activate origin LV as snapshot-merge target.  Using snapshot-origin
target would be pointless because the origin contains volatile data
while a merge is in progress.

Because snapshot-merge target is activated in place of the
snapshot-origin target it must be resumed after all other snapshots
(just like snapshot-origin does) --- otherwise small window for data
corruption would exist.

Ideally the merging snapshot would not be activated at all but if it is
to be activated (because snapshot was already active) it _must_ be done
after the snapshot-merge.  This insures that DM's snapshot-merge target
will perform exception handover in the proper order (new->resume before
old->resume).  DM's snapshot-merge does support handover if the reverse
sequence is used (old->resume before new->resume) but DM will fail to
resume the old snapshot; leaving it suspended.

To insure the proper activation sequence dm_tree_activate_children() was
updated to accommodate an additional 'activation_priority' level.  All
regular snapshots are 0, snapshot-merge is 1, and merging snapshot is 2.
This commit is contained in:
Mike Snitzer 2010-01-13 01:39:44 +00:00
parent 68e8f5a4a2
commit aa6f4e51a7
4 changed files with 78 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
lib/snapshot/snapshot.c
View File

@ -130,17 +130,25 @@ static int _snap_target_percent(void **target_state __attribute((unused)),
}
static int _snap_target_present(struct cmd_context *cmd,
const struct lv_segment *seg __attribute((unused)),
const struct lv_segment *seg,
unsigned *attributes __attribute((unused)))
{
static int _snap_checked = 0;
static int _snap_merge_checked = 0;
static int _snap_present = 0;
static int _snap_merge_present = 0;
if (!_snap_checked)
if (!_snap_checked) {
_snap_present = target_present(cmd, "snapshot", 1) &&
target_present(cmd, "snapshot-origin", 0);
_snap_checked = 1;
}
_snap_checked = 1;
if (!_snap_merge_checked && seg && (seg->status & SNAPSHOT_MERGE)) {
_snap_merge_present = target_present(cmd, "snapshot-merge", 0);
_snap_merge_checked = 1;
return _snap_present && _snap_merge_present;
}
return _snap_present;
}

1
libdm/.exported_symbols
View File

@ -71,6 +71,7 @@ dm_tree_suspend_children
dm_tree_children_use_uuid
dm_tree_node_add_snapshot_origin_target
dm_tree_node_add_snapshot_target
dm_tree_node_add_snapshot_merge_target
dm_tree_node_add_error_target
dm_tree_node_add_zero_target
dm_tree_node_add_linear_target

6
libdm/libdevmapper.h
View File

@ -394,6 +394,12 @@ int dm_tree_node_add_snapshot_target(struct dm_tree_node *node,
const char *cow_uuid,
int persistent,
uint32_t chunk_size);
int dm_tree_node_add_snapshot_merge_target(struct dm_tree_node *node,
uint64_t size,
const char *origin_uuid,
const char *cow_uuid,
const char *merge_uuid,
uint32_t chunk_size);
int dm_tree_node_add_error_target(struct dm_tree_node *node,
uint64_t size);
int dm_tree_node_add_zero_target(struct dm_tree_node *node,

70
libdm/libdm-deptree.c
View File

@ -35,6 +35,7 @@ enum {
SEG_MIRRORED,
SEG_SNAPSHOT,
SEG_SNAPSHOT_ORIGIN,
SEG_SNAPSHOT_MERGE,
SEG_STRIPED,
SEG_ZERO,
};
@ -51,6 +52,7 @@ struct {
{ SEG_MIRRORED, "mirror" },
{ SEG_SNAPSHOT, "snapshot" },
{ SEG_SNAPSHOT_ORIGIN, "snapshot-origin" },
{ SEG_SNAPSHOT_MERGE, "snapshot-merge" },
{ SEG_STRIPED, "striped" },
{ SEG_ZERO, "zero"},
};
@ -81,6 +83,7 @@ struct load_segment {
uint32_t chunk_size; /* Snapshot */
struct dm_tree_node *cow; /* Snapshot */
struct dm_tree_node *origin; /* Snapshot + Snapshot origin */
struct dm_tree_node *merge; /* Snapshot */
struct dm_tree_node *log; /* Mirror */
uint32_t region_size; /* Mirror */
@ -1179,7 +1182,7 @@ int dm_tree_activate_children(struct dm_tree_node *dnode,
handle = NULL;
for (priority = 0; priority < 2; priority++) {
for (priority = 0; priority < 3; priority++) {
while ((child = dm_tree_next_child(&handle, dnode, 0))) {
if (!(uuid = dm_tree_node_get_uuid(child))) {
stack;
@ -1471,6 +1474,7 @@ static int _emit_segment_line(struct dm_task *dmt, uint32_t major,
return_0;
break;
case SEG_SNAPSHOT:
case SEG_SNAPSHOT_MERGE:
if (!_build_dev_string(originbuf, sizeof(originbuf), seg->origin))
return_0;
if (!_build_dev_string(cowbuf, sizeof(cowbuf), seg->cow))
@ -1499,6 +1503,7 @@ static int _emit_segment_line(struct dm_task *dmt, uint32_t major,
case SEG_ERROR:
case SEG_SNAPSHOT:
case SEG_SNAPSHOT_ORIGIN:
case SEG_SNAPSHOT_MERGE:
case SEG_ZERO:
break;
case SEG_CRYPT:
@ -1735,6 +1740,7 @@ static struct load_segment *_add_segment(struct dm_tree_node *dnode, unsigned ty
seg->chunk_size = 0;
seg->cow = NULL;
seg->origin = NULL;
seg->merge = NULL;
dm_list_add(&dnode->props.segs, &seg->list);
dnode->props.segment_count++;
@ -1767,17 +1773,21 @@ int dm_tree_node_add_snapshot_origin_target(struct dm_tree_node *dnode,
return 1;
}
int dm_tree_node_add_snapshot_target(struct dm_tree_node *node,
uint64_t size,
const char *origin_uuid,
const char *cow_uuid,
int persistent,
uint32_t chunk_size)
static int _add_snapshot_target(struct dm_tree_node *node,
uint64_t size,
const char *origin_uuid,
const char *cow_uuid,
const char *merge_uuid,
int persistent,
uint32_t chunk_size)
{
struct load_segment *seg;
struct dm_tree_node *origin_node, *cow_node;
struct dm_tree_node *origin_node, *cow_node, *merge_node;
unsigned seg_type;
if (!(seg = _add_segment(node, SEG_SNAPSHOT, size)))
seg_type = !merge_uuid ? SEG_SNAPSHOT : SEG_SNAPSHOT_MERGE;
if (!(seg = _add_segment(node, seg_type, size)))
return_0;
if (!(origin_node = dm_tree_find_node_by_uuid(node->dtree, origin_uuid))) {
@ -1790,7 +1800,7 @@ int dm_tree_node_add_snapshot_target(struct dm_tree_node *node,
return_0;
if (!(cow_node = dm_tree_find_node_by_uuid(node->dtree, cow_uuid))) {
log_error("Couldn't find snapshot origin uuid %s.", cow_uuid);
log_error("Couldn't find snapshot COW device uuid %s.", cow_uuid);
return 0;
}
@ -1801,9 +1811,49 @@ int dm_tree_node_add_snapshot_target(struct dm_tree_node *node,
seg->persistent = persistent ? 1 : 0;
seg->chunk_size = chunk_size;
if (merge_uuid) {
if (!(merge_node = dm_tree_find_node_by_uuid(node->dtree, merge_uuid))) {
/* not a pure error, merging snapshot may have been deactivated */
log_verbose("Couldn't find merging snapshot uuid %s.", merge_uuid);
} else {
seg->merge = merge_node;
/* must not link merging snapshot, would undermine activation_priority below */
}
/* Resume snapshot-merge (acting origin) after other snapshots */
node->activation_priority = 1;
if (seg->merge) {
/* Resume merging snapshot after snapshot-merge */
seg->merge->activation_priority = 2;
}
}
return 1;
}
int dm_tree_node_add_snapshot_target(struct dm_tree_node *node,
uint64_t size,
const char *origin_uuid,
const char *cow_uuid,
int persistent,
uint32_t chunk_size)
{
return _add_snapshot_target(node, size, origin_uuid, cow_uuid,
NULL, persistent, chunk_size);
}
int dm_tree_node_add_snapshot_merge_target(struct dm_tree_node *node,
uint64_t size,
const char *origin_uuid,
const char *cow_uuid,
const char *merge_uuid,
uint32_t chunk_size)
{
return _add_snapshot_target(node, size, origin_uuid, cow_uuid,
merge_uuid, 1, chunk_size);
}
int dm_tree_node_add_error_target(struct dm_tree_node *node,
uint64_t size)
{