Add a blocking read function for readers. An irq_work function is used to signal the wait queue so that write notification can be triggered from any context.
Signed-off-by: John Ogness <[email protected]> --- include/linux/printk_ringbuffer.h | 20 ++++++++++++++++ lib/printk_ringbuffer.c | 49 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 69 insertions(+) diff --git a/include/linux/printk_ringbuffer.h b/include/linux/printk_ringbuffer.h index 5fdaf632c111..106f20ef8b4d 100644 --- a/include/linux/printk_ringbuffer.h +++ b/include/linux/printk_ringbuffer.h @@ -2,8 +2,10 @@ #ifndef _LINUX_PRINTK_RINGBUFFER_H #define _LINUX_PRINTK_RINGBUFFER_H +#include <linux/irq_work.h> #include <linux/atomic.h> #include <linux/percpu.h> +#include <linux/wait.h> struct prb_cpulock { atomic_t owner; @@ -22,6 +24,10 @@ struct printk_ringbuffer { struct prb_cpulock *cpulock; atomic_t ctx; + + struct wait_queue_head *wq; + atomic_long_t wq_counter; + struct irq_work *wq_work; }; struct prb_entry { @@ -59,6 +65,15 @@ struct prb_iterator { #define DECLARE_STATIC_PRINTKRB(name, szbits, cpulockptr) \ static char _##name##_buffer[1 << (szbits)] \ __aligned(__alignof__(long)); \ +static DECLARE_WAIT_QUEUE_HEAD(_##name##_wait); \ +static void _##name##_wake_work_func(struct irq_work *irq_work) \ +{ \ + wake_up_interruptible_all(&_##name##_wait); \ +} \ +static struct irq_work _##name##_wake_work = { \ + .func = _##name##_wake_work_func, \ + .flags = IRQ_WORK_LAZY, \ +}; \ static struct printk_ringbuffer name = { \ .buffer = &_##name##_buffer[0], \ .size_bits = szbits, \ @@ -68,6 +83,9 @@ static struct printk_ringbuffer name = { \ .reserve = ATOMIC_LONG_INIT(-111 * sizeof(long)), \ .cpulock = cpulockptr, \ .ctx = ATOMIC_INIT(0), \ + .wq = &_##name##_wait, \ + .wq_counter = ATOMIC_LONG_INIT(0), \ + .wq_work = &_##name##_wake_work, \ } /* writer interface */ @@ -80,6 +98,8 @@ void prb_iter_init(struct prb_iterator *iter, struct printk_ringbuffer *rb, u64 *seq); void prb_iter_copy(struct prb_iterator *dest, struct prb_iterator *src); int prb_iter_next(struct prb_iterator *iter, char *buf, int size, u64 *seq); +int prb_iter_wait_next(struct prb_iterator *iter, char *buf, int size, + u64 *seq); int prb_iter_data(struct prb_iterator *iter, char *buf, int size, u64 *seq); /* utility functions */ diff --git a/lib/printk_ringbuffer.c b/lib/printk_ringbuffer.c index 1d1e886a0966..c2ddf4cb9f92 100644 --- a/lib/printk_ringbuffer.c +++ b/lib/printk_ringbuffer.c @@ -1,4 +1,5 @@ // SPDX-License-Identifier: GPL-2.0 +#include <linux/sched.h> #include <linux/smp.h> #include <linux/string.h> #include <linux/errno.h> @@ -154,6 +155,7 @@ static bool push_tail(struct printk_ringbuffer *rb, unsigned long tail) void prb_commit(struct prb_handle *h) { struct printk_ringbuffer *rb = h->rb; + bool changed = false; struct prb_entry *e; unsigned long head; unsigned long res; @@ -175,6 +177,7 @@ void prb_commit(struct prb_handle *h) } e->seq = ++rb->seq; head += e->size; + changed = true; } atomic_long_set_release(&rb->head, res); atomic_dec(&rb->ctx); @@ -185,6 +188,12 @@ void prb_commit(struct prb_handle *h) } prb_unlock(rb->cpulock, h->cpu); + + if (changed) { + atomic_long_inc(&rb->wq_counter); + if (wq_has_sleeper(rb->wq)) + irq_work_queue(rb->wq_work); + } } /* @@ -437,3 +446,43 @@ int prb_iter_next(struct prb_iterator *iter, char *buf, int size, u64 *seq) return 1; } + +/* + * prb_iter_wait_next: Advance to the next record, blocking if none available. + * @iter: Iterator tracking the current position. + * @buf: A buffer to store the data of the next record. May be NULL. + * @size: The size of @buf. (Ignored if @buf is NULL.) + * @seq: The sequence number of the next record. May be NULL. + * + * If a next record is already available, this function works like + * prb_iter_next(). Otherwise block interruptible until a next record is + * available. + * + * When a next record is available, @iter is advanced and (if specified) + * the data and/or sequence number of that record are provided. + * + * This function might sleep. + * + * Returns 1 if @iter was advanced, -EINVAL if @iter is now invalid, or + * -ERESTARTSYS if interrupted by a signal. + */ +int prb_iter_wait_next(struct prb_iterator *iter, char *buf, int size, u64 *seq) +{ + unsigned long last_seen; + int ret; + + for (;;) { + last_seen = atomic_long_read(&iter->rb->wq_counter); + + ret = prb_iter_next(iter, buf, size, seq); + if (ret != 0) + break; + + ret = wait_event_interruptible(*iter->rb->wq, + last_seen != atomic_long_read(&iter->rb->wq_counter)); + if (ret < 0) + break; + } + + return ret; +} -- 2.11.0
