Commit 3cdf93f9 authored by Joe Thornber's avatar Joe Thornber Committed by Mike Snitzer

dm bio prison: add dm_cell_promote_or_release()

Rather than always releasing the prisoners in a cell, the client may
want to promote one of them to be the new holder.  There is a race here
though between releasing an empty cell, and other threads adding new
inmates.  So this function makes the decision with its lock held.

This function can have two outcomes:
i)  An inmate is promoted to be the holder of the cell (return value of 0).
ii) The cell has no inmate for promotion and is released (return value of 1).
Signed-off-by: default avatarJoe Thornber <ejt@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
parent 451b9e00
......@@ -255,6 +255,32 @@ void dm_cell_visit_release(struct dm_bio_prison *prison,
}
EXPORT_SYMBOL_GPL(dm_cell_visit_release);
static int __promote_or_release(struct dm_bio_prison *prison,
struct dm_bio_prison_cell *cell)
{
if (bio_list_empty(&cell->bios)) {
rb_erase(&cell->node, &prison->cells);
return 1;
}
cell->holder = bio_list_pop(&cell->bios);
return 0;
}
int dm_cell_promote_or_release(struct dm_bio_prison *prison,
struct dm_bio_prison_cell *cell)
{
int r;
unsigned long flags;
spin_lock_irqsave(&prison->lock, flags);
r = __promote_or_release(prison, cell);
spin_unlock_irqrestore(&prison->lock, flags);
return r;
}
EXPORT_SYMBOL_GPL(dm_cell_promote_or_release);
/*----------------------------------------------------------------*/
#define DEFERRED_SET_SIZE 64
......
......@@ -101,6 +101,19 @@ void dm_cell_visit_release(struct dm_bio_prison *prison,
void (*visit_fn)(void *, struct dm_bio_prison_cell *),
void *context, struct dm_bio_prison_cell *cell);
/*
* Rather than always releasing the prisoners in a cell, the client may
* want to promote one of them to be the new holder. There is a race here
* though between releasing an empty cell, and other threads adding new
* inmates. So this function makes the decision with its lock held.
*
* This function can have two outcomes:
* i) An inmate is promoted to be the holder of the cell (return value of 0).
* ii) The cell has no inmate for promotion and is released (return value of 1).
*/
int dm_cell_promote_or_release(struct dm_bio_prison *prison,
struct dm_bio_prison_cell *cell);
/*----------------------------------------------------------------*/
/*
......
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