From e7d553d69cf63aec7de0f38fed49ccbb30922e1e Mon Sep 17 00:00:00 2001 From: David Howells Date: Tue, 14 Jan 2020 17:07:12 +0000 Subject: [PATCH] pipe: Add notification lossage handling Add handling for loss of notifications by having read() insert a loss-notification message after it has read the pipe buffer that was last in the ring when the loss occurred. Lossage can come about either by running out of notification descriptors or by running out of space in the pipe ring. Signed-off-by: David Howells --- fs/pipe.c | 28 ++++++++++++++++++++++++++++ include/linux/pipe_fs_i.h | 7 +++++++ kernel/watch_queue.c | 2 ++ samples/watch_queue/watch_test.c | 3 +++ 4 files changed, 40 insertions(+) diff --git a/fs/pipe.c b/fs/pipe.c index 0f9fd89..620a113 100644 --- a/fs/pipe.c +++ b/fs/pipe.c @@ -314,6 +314,30 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to) unsigned int tail = pipe->tail; unsigned int mask = pipe->ring_size - 1; +#ifdef CONFIG_WATCH_QUEUE + if (pipe->note_loss) { + struct watch_notification n; + + if (total_len < 8) { + if (ret == 0) + ret = -ENOBUFS; + break; + } + + n.type = WATCH_TYPE_META; + n.subtype = WATCH_META_LOSS_NOTIFICATION; + n.info = watch_sizeof(n); + if (copy_to_iter(&n, sizeof(n), to) != sizeof(n)) { + if (ret == 0) + ret = -EFAULT; + break; + } + ret += sizeof(n); + total_len -= sizeof(n); + pipe->note_loss = false; + } +#endif + if (!pipe_empty(head, tail)) { struct pipe_buffer *buf = &pipe->bufs[tail & mask]; size_t chars = buf->len; @@ -355,6 +379,10 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to) if (!buf->len) { pipe_buf_release(pipe, buf); spin_lock_irq(&pipe->rd_wait.lock); +#ifdef CONFIG_WATCH_QUEUE + if (buf->flags & PIPE_BUF_FLAG_LOSS) + pipe->note_loss = true; +#endif tail++; pipe->tail = tail; spin_unlock_irq(&pipe->rd_wait.lock); diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h index eaff59a..6626f51 100644 --- a/include/linux/pipe_fs_i.h +++ b/include/linux/pipe_fs_i.h @@ -9,6 +9,9 @@ #define PIPE_BUF_FLAG_GIFT 0x04 /* page is a gift */ #define PIPE_BUF_FLAG_PACKET 0x08 /* read() as a packet */ #define PIPE_BUF_FLAG_WHOLE 0x10 /* read() must return entire buffer or error */ +#ifdef CONFIG_WATCH_QUEUE +#define PIPE_BUF_FLAG_LOSS 0x20 /* Message loss happened after this buffer */ +#endif /** * struct pipe_buffer - a linux kernel pipe buffer @@ -34,6 +37,7 @@ struct pipe_buffer { * @wr_wait: writer wait point in case of full pipe * @head: The point of buffer production * @tail: The point of buffer consumption + * @note_loss: The next read() should insert a data-lost message * @max_usage: The maximum number of slots that may be used in the ring * @ring_size: total number of buffers (should be a power of 2) * @nr_accounted: The amount this pipe accounts for in user->pipe_bufs @@ -56,6 +60,9 @@ struct pipe_inode_info { unsigned int tail; unsigned int max_usage; unsigned int ring_size; +#ifdef CONFIG_WATCH_QUEUE + bool note_loss; +#endif unsigned int nr_accounted; unsigned int readers; unsigned int writers; diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c index ad64ea30..9a9699c 100644 --- a/kernel/watch_queue.c +++ b/kernel/watch_queue.c @@ -132,6 +132,8 @@ out: return done; lost: + buf = &pipe->bufs[(head - 1) & mask]; + buf->flags |= PIPE_BUF_FLAG_LOSS; goto out; } diff --git a/samples/watch_queue/watch_test.c b/samples/watch_queue/watch_test.c index 8628b4c..46e618a 100644 --- a/samples/watch_queue/watch_test.c +++ b/samples/watch_queue/watch_test.c @@ -120,6 +120,9 @@ static void consumer(int fd) (n.n.info & WATCH_INFO_ID) >> WATCH_INFO_ID__SHIFT); break; + case WATCH_META_LOSS_NOTIFICATION: + printf("-- LOSS --\n"); + break; default: printf("other meta record\n"); break; -- 2.7.4