Commit e7d553d6 authored by David Howells's avatar David Howells

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: default avatarDavid Howells <dhowells@redhat.com>
parent 8cfba763
...@@ -314,6 +314,30 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to) ...@@ -314,6 +314,30 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
unsigned int tail = pipe->tail; unsigned int tail = pipe->tail;
unsigned int mask = pipe->ring_size - 1; 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)) { if (!pipe_empty(head, tail)) {
struct pipe_buffer *buf = &pipe->bufs[tail & mask]; struct pipe_buffer *buf = &pipe->bufs[tail & mask];
size_t chars = buf->len; size_t chars = buf->len;
...@@ -355,6 +379,10 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to) ...@@ -355,6 +379,10 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
if (!buf->len) { if (!buf->len) {
pipe_buf_release(pipe, buf); pipe_buf_release(pipe, buf);
spin_lock_irq(&pipe->rd_wait.lock); spin_lock_irq(&pipe->rd_wait.lock);
#ifdef CONFIG_WATCH_QUEUE
if (buf->flags & PIPE_BUF_FLAG_LOSS)
pipe->note_loss = true;
#endif
tail++; tail++;
pipe->tail = tail; pipe->tail = tail;
spin_unlock_irq(&pipe->rd_wait.lock); spin_unlock_irq(&pipe->rd_wait.lock);
......
...@@ -9,6 +9,9 @@ ...@@ -9,6 +9,9 @@
#define PIPE_BUF_FLAG_GIFT 0x04 /* page is a gift */ #define PIPE_BUF_FLAG_GIFT 0x04 /* page is a gift */
#define PIPE_BUF_FLAG_PACKET 0x08 /* read() as a packet */ #define PIPE_BUF_FLAG_PACKET 0x08 /* read() as a packet */
#define PIPE_BUF_FLAG_WHOLE 0x10 /* read() must return entire buffer or error */ #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 * struct pipe_buffer - a linux kernel pipe buffer
...@@ -34,6 +37,7 @@ struct pipe_buffer { ...@@ -34,6 +37,7 @@ struct pipe_buffer {
* @wr_wait: writer wait point in case of full pipe * @wr_wait: writer wait point in case of full pipe
* @head: The point of buffer production * @head: The point of buffer production
* @tail: The point of buffer consumption * @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 * @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) * @ring_size: total number of buffers (should be a power of 2)
* @nr_accounted: The amount this pipe accounts for in user->pipe_bufs * @nr_accounted: The amount this pipe accounts for in user->pipe_bufs
...@@ -56,6 +60,9 @@ struct pipe_inode_info { ...@@ -56,6 +60,9 @@ struct pipe_inode_info {
unsigned int tail; unsigned int tail;
unsigned int max_usage; unsigned int max_usage;
unsigned int ring_size; unsigned int ring_size;
#ifdef CONFIG_WATCH_QUEUE
bool note_loss;
#endif
unsigned int nr_accounted; unsigned int nr_accounted;
unsigned int readers; unsigned int readers;
unsigned int writers; unsigned int writers;
......
...@@ -132,6 +132,8 @@ static bool post_one_notification(struct watch_queue *wqueue, ...@@ -132,6 +132,8 @@ static bool post_one_notification(struct watch_queue *wqueue,
return done; return done;
lost: lost:
buf = &pipe->bufs[(head - 1) & mask];
buf->flags |= PIPE_BUF_FLAG_LOSS;
goto out; goto out;
} }
......
...@@ -120,6 +120,9 @@ static void consumer(int fd) ...@@ -120,6 +120,9 @@ static void consumer(int fd)
(n.n.info & WATCH_INFO_ID) >> (n.n.info & WATCH_INFO_ID) >>
WATCH_INFO_ID__SHIFT); WATCH_INFO_ID__SHIFT);
break; break;
case WATCH_META_LOSS_NOTIFICATION:
printf("-- LOSS --\n");
break;
default: default:
printf("other meta record\n"); printf("other meta record\n");
break; break;
......
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