Alasdair,
This is an RFC patch that adds locking around each hash_cell's new_map.
It allows us to safely display the status/info of a DM device's INACTIVE
table. I haven't tied this in to userspace yet (see 'TODO' below) but
my intention is to add an --inactive flag, e.g.:
dmsetup status --inactive
dmsetup info --inactive
This is useful for seeing when a DM device is in the middle a complex
transition, e.g. snapshot-merge's exception handover:
Before snapshot-merge:
----------------------
# dmsetup status test-testlv
0 67108864 snapshot-origin
Snapshot-merge target created, about to handover exceptions:
------------------------------------------------------------
# dmsetup status test-testlv
0 67108864 snapshot-merge 16/14680064 16
NOTE: the snapshot-merge store is empty (handover hasn't happened yet)
After exception handover, before merge has started:
---------------------------------------------------
# dmsetup status test-testlv
0 67108864 snapshot-merge 1328904/14680064 5184
Snapshot-merge table is now active and is merging:
--------------------------------------------------
# dmsetup status test-testlv
0 67108864 snapshot-merge 1005392/14680064 3920
diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 8208b3a..17fc78d 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -34,6 +34,7 @@ struct hash_cell {
char *uuid;
struct mapped_device *md;
struct dm_table *new_map;
+ rwlock_t new_map_lock;
};
struct vers_iter {
@@ -157,6 +158,7 @@ static struct hash_cell *alloc_cell(const char *name, const char *uuid,
INIT_LIST_HEAD(&hc->uuid_list);
hc->md = md;
hc->new_map = NULL;
+ rwlock_init(&hc->new_map_lock);
return hc;
}
@@ -620,6 +622,26 @@ out:
return mdptr;
}
+static struct dm_table *dm_get_inactive_table(struct dm_ioctl *param)
+{
+ struct hash_cell *hc;
+ struct dm_table *table = NULL;
+ unsigned long flags;
+
+ down_read(&_hash_lock);
+ hc = __find_device_hash_cell(param);
+ if (hc) {
+ read_lock_irqsave(&hc->new_map_lock, flags);
+ table = hc->new_map;
+ if (table)
+ dm_table_get(table);
+ read_unlock_irqrestore(&hc->new_map_lock, flags);
+ }
+ up_read(&_hash_lock);
+
+ return table;
+}
+
static struct mapped_device *find_device(struct dm_ioctl *param)
{
struct hash_cell *hc;
@@ -798,6 +820,7 @@ static int do_resume(struct dm_ioctl *param)
{
int r = 0;
unsigned suspend_flags = DM_SUSPEND_LOCKFS_FLAG;
+ unsigned long flags;
struct hash_cell *hc;
struct mapped_device *md;
struct dm_table *new_map;
@@ -813,8 +836,10 @@ static int do_resume(struct dm_ioctl *param)
md = hc->md;
+ write_lock_irqsave(&hc->new_map_lock, flags);
new_map = hc->new_map;
hc->new_map = NULL;
+ write_unlock_irqrestore(&hc->new_map_lock, flags);
param->flags &= ~DM_INACTIVE_PRESENT_FLAG;
up_write(&_hash_lock);
@@ -1075,6 +1100,7 @@ static int table_prealloc_integrity(struct dm_table *t,
static int table_load(struct dm_ioctl *param, size_t param_size)
{
int r;
+ unsigned long flags;
struct hash_cell *hc;
struct dm_table *t;
struct mapped_device *md;
@@ -1118,9 +1144,11 @@ static int table_load(struct dm_ioctl *param, size_t param_size)
goto out;
}
+ write_lock_irqsave(&hc->new_map_lock, flags);
if (hc->new_map)
dm_table_destroy(hc->new_map);
hc->new_map = t;
+ write_unlock_irqrestore(&hc->new_map_lock, flags);
up_write(&_hash_lock);
param->flags |= DM_INACTIVE_PRESENT_FLAG;
@@ -1135,6 +1163,7 @@ out:
static int table_clear(struct dm_ioctl *param, size_t param_size)
{
int r;
+ unsigned long flags;
struct hash_cell *hc;
struct mapped_device *md;
@@ -1147,10 +1176,11 @@ static int table_clear(struct dm_ioctl *param, size_t param_size)
return -ENXIO;
}
- if (hc->new_map) {
+ write_lock_irqsave(&hc->new_map_lock, flags);
+ if (hc->new_map)
dm_table_destroy(hc->new_map);
- hc->new_map = NULL;
- }
+ hc->new_map = NULL;
+ write_unlock_irqrestore(&hc->new_map_lock, flags);
param->flags &= ~DM_INACTIVE_PRESENT_FLAG;
@@ -1226,6 +1256,21 @@ static int table_deps(struct dm_ioctl *param, size_t param_size)
return r;
}
+static struct dm_table* __dm_get_table(struct mapped_device *md,
+ struct dm_ioctl *param)
+{
+ struct dm_table *table;
+ /* TODO: make this conditional on user param --inactive,
+ e.g.: DM_STATUS_INACTIVE_FLAG
+ */
+ if (param->flags & DM_INACTIVE_PRESENT_FLAG) {
+ table = dm_get_inactive_table(param);
+ } else {
+ table = dm_get_table(md);
+ }
+ return table;
+}
+
/*
* Return the status of a device as a text string for each
* target.
@@ -1244,7 +1289,7 @@ static int table_status(struct dm_ioctl *param, size_t param_size)
if (r)
goto out;
- table = dm_get_table(md);
+ table = __dm_get_table(md, param);
if (table) {
retrieve_status(table, param, param_size);
dm_table_put(table);
--
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