[PATCH net-next v14 4/5] ptr_ring: move free-space check into separate helper
From: Simon Schippers <hidden>
Date: 2026-08-04 01:56:01
Also in:
kvm, linux-doc, lkml, virtualization
Subsystem:
the rest · Maintainer:
Linus Torvalds
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 <redacted> Signed-off-by: Tim Gebauer <redacted> Signed-off-by: Simon Schippers <redacted> --- include/linux/ptr_ring.h | 26 ++++++++++++++++++++++++-- 1 file changed, 24 insertions(+), 2 deletions(-)
diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
index d2c3629bbe45..631c43fde440 100644
--- a/include/linux/ptr_ring.h
+++ b/include/linux/ptr_ring.h@@ -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. */
--
2.43.0