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ptr_ring: move free-space check into separate helper

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This patch moves the check for available free space for a new entry into
a separate function. Existing callers that only check for a non-zero
return value are unaffected. __ptr_ring_produce() now returns -EINVAL
for a zero-size ring and -ENOSPC when full, whereas before both cases
returned -ENOSPC. The new helper allows callers to determine in advance
whether a single subsequent __ptr_ring_produce() call will succeed. This
information can, for example, be used to temporarily stop producing until
__ptr_ring_check_produce() indicates that space is available again.

The return values are documented above the helper, as a caller that waits
for space must distinguish the transient -ENOSPC from the permanent
-EINVAL.

Co-developed-by: Tim Gebauer <tim.gebauer@tu-dortmund.de>
Signed-off-by: Tim Gebauer <tim.gebauer@tu-dortmund.de>
Signed-off-by: Simon Schippers <simon.schippers@tu-dortmund.de>
Link: https://patch.msgid.link/20260803183641.96882-5-simon.schippers@tu-dortmund.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Simon Schippers
2026-08-03 20:36:40 +02:00
committed by Jakub Kicinski
parent f65c1fb427
commit 43be21ec2e
1 changed files with 24 additions and 2 deletions
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26
include/linux/ptr_ring.h
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@@ -96,6 +96,26 @@ static inline bool ptr_ring_full_bh(struct ptr_ring *r)
return ret;
}
/* Report whether the next __ptr_ring_produce() has room for one entry:
* 0 means the single slot at r->queue[r->producer] is free, -ENOSPC means
* the ring is full, which is transient, and -EINVAL means r->size is 0,
* which is permanent. A caller that stops producing and waits for space
* must therefore do so only for -ENOSPC.
*
* Note: callers invoking this in a loop must use a compiler barrier,
* for example cpu_relax(). Callers must hold producer_lock.
*/
static inline int __ptr_ring_check_produce(struct ptr_ring *r)
{
if (unlikely(!r->size))
return -EINVAL;
if (data_race(r->queue[r->producer]))
return -ENOSPC;
return 0;
}
/* Note: callers invoking this in a loop must use a compiler barrier,
* for example cpu_relax(). Callers must hold producer_lock.
* Callers are responsible for making sure pointer that is being queued
@@ -103,8 +123,10 @@ static inline bool ptr_ring_full_bh(struct ptr_ring *r)
*/
static inline int __ptr_ring_produce(struct ptr_ring *r, void *ptr)
{
if (unlikely(!r->size) || data_race(r->queue[r->producer]))
return -ENOSPC;
int ret = __ptr_ring_check_produce(r);
if (ret)
return ret;
/* Make sure the pointer we are storing points to a valid data. */
/* Pairs with the dependency ordering in __ptr_ring_consume. */